book of abtracts erem 6th

6TH SYMPOSIUM ON ELECTROKINETIC REMEDIATION

Vigo (Spain) 12-15th June 2007

Book of Abstracts

Organized by BIOPROCESS RESEARCH GROUP

University of Vigo. Dept. of Chemical Engineering Building Isaac Newton. 36310 Vigo. Spain

phone: +34 986 812318 - fax: +34 986 812380 e-mail: [email protected]

Editors: Claudio Cameselle Fernández Mª Angeles Sanromán Braga Marta María Pazos Currás

University of Vigo Dept. of Chemical Engineering Building Isaac Newton 36310 Vigo. Spain

Depósito Legal: VG-586-2007

Scientific Committee

Lisbeth Ottosen Technical University of Denmark. Lyngby, Denmark.

Sibel Pamucku Lehigh University. Lehigh, Pennsylvania, USA.

Ji Won Yang Korean Advanced Institute of Science and Technology. Daejeon, Korea.

Henrik K. Hansen Technical University Federico Santa María. Valparaíso, Chile.

Achille De Battisti University of Ferrara. Ferrara, Italy.

Roman Zorn Karlsruhe University. Karlsruhe, Germany.

Djamal Akretche USTHB. Algiers, Algeria.

Mª Angeles Sanromán Braga University of Vigo. Vigo, Spain.

Claudio Cameselle Fernández University of Vigo. Vigo, Spain.

Marta María Pazos Currás University of Vigo. Vigo, Spain.

Organizing Committee

Claudio Cameselle Fernández (Coordinator of the organizing committee)

Mª Ángeles Sanromán Braga Fátima Moscoso Díaz

Marta Mª Pazos Currás Iria Vazquez Rodríguez

Mª Teresa Ricart Ricart María Barreiro Miranda

Mª Teresa Alcántara López Francisco Javier Deive Herva

José Gómez Sieiro Arístides Huerga Vázquez

Susana Ferreira de Gouveia María Rivera Sobrado

EREM 2007 Secretariat

University of Vigo Dept. of Chemical Engineering Building Isaac Newton 36310 Vigo. Spain e-mail: [email protected] phone: +34 986 812318 fax: +34 986 812380

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Conference Venue

The conference will be held in "Centro Social Caixanova". The organizers appreciate very much the help of CAIXANOVA in the organization of EREM 2007.

Centro Social Caixanova

Sponsors

Ministry of Education and Science (CTM2006-26215-E/TECNO)

Caixanova

University of Vigo

City of Vigo

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http://www.caixanova.es/

Programme

12th JUNE 2007

17:00-20:00 Registration and Poster set-up.

13th JUNE 2007

9:00-9:30 Conference Opening 9:30-10:00 Plenary Lecture

Sustainable soil remediation. The use of combined technologies. M.C. Lobo (IMIDRA, Spain)

10:00-11:20 Session 1: Electrokinetic Barriers 11:20-11:50 Coffee Break - Poster Session 11:50-12:20 Plenary Lecture

Utilization of electromigration in civil and environmental engineering. Lisbeth M. Ottosen (DTU, Denmark)

11.20-14:00 Session 2: Metal Removal 14:00-16:00 Lunch - Poster Session 16:00-18:50 Session 3: New Applications – Inorganic Pollutants 20:00-21:00 Reception and cocktail in the gardens of the Museum "Quiñones de

León"

14th JUNE 2007

8:30-10:30 Session 4: New Applications – Bioremediation 10:30-11:00 Coffee Break - Poster Session 11:00-11:30 Plenary Lecture

Electrokinetic delivery of nanoscale iron particles for remediation of pentachlorophenol in clayey soil Krishna R. Reddy (Univ. of Illinois at Chicago, USA)

11:30-13:10 Session 5: Organic Pollutants 13:10-15:00 Lunch 15:00-15:30 Plenary Lecture

Electroremediation – Where do we go now? Henrik K. Hansen (Univ. Técnica Federico Santa María, Chile)

15:30-16:50 Session 6: Modelling and other Applications 16:50-17:20 Coffee Break - Poster Session 17:20-18:20 Session 7: Electrokinetic and Electrochemical Degradation 18:20-18:30 Conference Closure 21:00 Social Dinner

15th JUNE 2007

10:30-19:00 Guided Tour to the Cies Islands

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http://www.museodevigo.org/

http://www.museodevigo.org/

Programme – Oral Presentations

13th JUNE 2007 9:00-9:30 Conference Opening 9:30-10:00 Plenary Lecture

Sustainable soil remediation. The use of combined technologies. M.C. Lobo

Session 1: Electrokinetic Barriers 10:00-10:20 In-situ electrokinetic permeable reactive barrier: field investigation in the

vicinity of unregulated landfill site. MyungHo Lee and Ha-Ik Chung

10:20-10:40 Chromate adsorbtion in a transformed red mud permeable reactive barrier using electrokinesis. Giorgia De Gioannis, Aldo Muntoni, Romano Ruggeri, Hans Zijlstra and Matteo Floris

10:40-11:00 Electrokinetic permeable reactive barrier for the removal of heavy metal and organic substance in contaminated soil and groundwater. Ha Ik Chung, Yong Soo Lee

11:00-11:20 Use of a pulsed electric field for resisting groundwater pollution. J Reeve and R J Lynch

11:20-11:50 Coffee Break - Poster Session 11:50-12:20 Plenary Lecture

Utilization of electromigration in civil and environmental engineering. Lisbeth M. Ottosen, Iben V. Christensen, Inge Rörig-Dalgård, Pernille E. Jensen

Session 2: Metal Removal 12:20-12:40 Phosphation of bottom-ash from MSWI by means of electrokinetics.

G. Traina, S. Ferro, A. De Battisti 12:40-13:00 Electrodialytic removal of toxic elements from sediments of eutrophic fresh

waters. Pernille E. Jensen, Lisbeth M. Ottosen, Arne Villumsen

13:00-13:20 Enhanced electrokinetic treatment of different marine sediments contaminated by heavy metals. De Gioannis Giorgia, Muntoni Aldo, Polettini Alessandra, Pomi Raffaella

13:20-13:40 Electroremediation of an industrial area contaminated by chromium. O. Merdoud and D. E. Akretche

13:40-14:00 Bench scale evaluation of hexavalent chromium reduction and containment using firs (ferric iron remediation and stabilisation) technology. Anne Hansen, Laurence Hopkinson, Andrew Cundy, Ross Pollock

14:00-16:00 Lunch - Poster Session

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13th JUNE 2007 Session 3: New Applications – Inorganic Pollutants 16:00-16:20 Delivery and activation of nano-iron by DC electric field.

Sibel Pamukcu, Laura Hannum, J.Kenneth Wittle16:20-16:40 Electro-reclamation of cyanide, impossibility or opportunity?

Bas Godschalk, Wiebe Pool 16:40-17:00 Electrokinetically enhanced removal and degradation of nitrate in the

subsurface using nanosized pd/fe slurry. Gordon C. C. Yang, Chih-Hsiung Hung, Hsiu-Chuan Tu

17:00-17:20 Spent caustic oxidation using electrogenerated Fenton’s reagent in a batch reactor. Henrik Hansen, Patricio Nuñez, Nicolás Rodríguez

17:20-17:40 Physicochemical study of clay soil using inert and steel electrodes. C. Liaki, C.D.F. Rogers and D.I. Boardman

17:40-18:00 Microstructural changes in a cementitious membrane due to the application of an electrical field. A. Covelo, B. Díaz, L. Freire, X. R. Nóvoa, M. C. Pérez

18:00-18:20 Effect of the electrolysis time in the movement of nitrates in an andisol of Antioquía (Colombia). Diego A. Vasco, Felipe Hernández-Luis, Carmen D. Arbelo, Mario V. Vázquez

18:30-18:50 Comparative cost analysis of the electro-Fenton and the photoelectro-Fenton processes. Ahmet Altin, Eyüp Atmaca, Süreyya Altin, Vural Evren

14th JUNE 2007

Session 4: New Applications – Bioremediation 8:30-8:50 Assessment of electrode materials for an integrated bio-electro-process.

Lohner S.T., Becker D., Schell H., Augenstein T., Weidlich C. 8:30-9:10 Electrokinetic transport and processing of bone repair agents.

Henry E. Cardenas, Satya S.Vasam, Yu Zhao, Deepika Morishetti 9:10-9:30 Electro-bioremediation: influence of direct current on the physiology and

dispersion of pollutant degrading bacteria in model soil. Lei Shi, Susann Müller, Hauke Harms, Lukas Y. Wick

9:30-9:50 Electrokinetic remediation of biosolids through inactivation of Clostridium perfringens spores. Maria Elektorowicz*, Elham Safaei, Jan Oleszkiewicz, Robert Reimers

9:50-10:10 Electrokinetic enhancement of phytoremediation in Zn, Cd, Cu and Pb contaminated soil using potato plants. R. Bi, H. Aboughalma, M. Schlaak

10:10-10:30 Tetrachloroethylene bioremediation by electrochemical injection of an electron donor. Xingzhi Wu, David B.Gent, Akram Alshawabkeh Jeffrey L. Davis

10:30-11:00 Coffee Break - Poster Session 11:00-11:30 Plenary Lecture

Electrokinetic delivery of nanoscale iron particles for remediation of pentachlorophenol in clayey soil. Krishna R. Reddy, Amid P. Khodadoust, and Madhusudhana R. Karri

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14th JUNE 2007 Session 5: Organic Pollutants 11:30-11:50 Influence of electroosmotic flow on the PAH release from model soil

matrices. Lei Shi, Hauke Harms, Lukas Wick

11:50-12:10 Electrokinetic removal of molinate from soils: experimental and modeling. A. B. Ribeiro, J. S. Santos, E. P. Mateus, J. M. Rodríguez-Maroto, M. D. R. Gomes da Silva, L. M. Ottosen

12:10-12:30 Remediation of hexachlorobenzene in soil by enhanced electrokinetic Fenton process. Oonnittan, A., Shrestha, R., Sillanpää, M.

12:30-12:50

Integrated electrokinetic process with BDD electrode for degradation of phenol from contaminated soil. You-Jin Lee, Jong-Young Choi, Ji-Won Yang

12:50-13:10 Electrokinetic remediation of the oil-contaminated soils. V. A. Korolev, O.V. Romanyukha & A.M. Abyzova

13:10-15:00 Lunch 15:00-15:30 Plenary Lecture

Electroremediation – Where do we go now? Henrik K. Hansen

Session 6: Modelling and other Applications 15:30-15:50 Prediction of the performance of EKR based on speciation analysis and

mathematical modeling. C. Vereda-Alonso, A. García-Rubio, C. Gómez-Lahoz, J. M. Rodríguez-Maroto and F. García-Herruzo

15:50-16:10 Electrokinetic remediation model: electric resistivity heating with dc electric fields. Zorn, R., & Steger, H.

16:10-16:30 Strengthening of soft clay with electrokinetic stabilization method. Dilek Turer, Ayten Genc

16:30-16:50 Induced electrical gradients by hyperfiltration in clays. J.P. Gustav Loch and Katja Heister

16:50-17:20 Coffee break – Poster Session Session 7: Electrokinetic and Electrochemical Degradation 17:20-17:40 Electrochemical treatment of pharmaceutical wastewater by combining

electrochemical oxidation with ozonation. Menapace, Hannes; Díaz, Nicolás

17:40-18:00 Soil remediation by electro synthesis of oxidants and their electrokinetic distribution. Heidi Mikkola, Wolfgang Wesner, Julia Schmale, Slagjana Petkovska

18:00-18:20 On site and in situ production of oxidants for soil remediation. W. Wesner, A. Diamant, B. Schrammel, M. Unterberger, H. Mikkola

18:20-18:30 Conference Closure

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Modifications to the Programme

Non-delivered Oral Presentations Session 1: Electrokinetic Barriers 10:40-11:00

S13 Electrokinetic permeable reactive barrier for the removal of heavy metal and organic substance in contaminated soil and groundwater. Ha Ik Chung, Yong Soo Lee

Session 3: New Applications – Inorganic Pollutants 16:20-16:40

S32 Electro-reclamation of cyanide, impossibility or opportunity? Bas Godschalk, Wiebe Pool

Session 5: Organic Pollutants 11:50-12:10

S52 Electrokinetic removal of molinate from soils: experimental and modeling. A. B. Ribeiro, J. S. Santos, E. P. Mateus, J. M. Rodríguez-Maroto, M. D. R. Gomes da Silva, L. M. Ottosen

Session 6: Modelling and other Applications 15:30-15:50

S61 Prediction of the performance of EKR based on speciation analysis and mathematical modeling. C. Vereda-Alonso, A. García-Rubio, C. Gómez-Lahoz, J. M. Rodríguez-Maroto and F. García-Herruzo

New Oral Presentations Session 6: Modelling and other Applications 15:30-15:50

P46 From electroremediation to metal valorisation. N. Sabba and D. E. Akretche

New Posters P47 Dewatering of Tunnelling Slurry Waste using Electrokinetic Geosynthetics

Denis Kalumba1,*, Stephanie Glendinning1, Chris D. F. Rogers2, David I. Boardman2, Mark Tyrer3 and Alan Atkinson3

1Newcastle University, 2University of Birmingham and 3Imperial College, London (*Correspondence: [email protected] )

P48 Speciation Of Heavy Metals In Sludge, Dewatered By Electrokinetik Process, Using

VISUAL MINTEQ Abdoli H.1, Esmaeily A.1, Elektorowicz M.1, Oleszkiewicz J.21 Department of Building, Civil and Environmental Engineering, Concordia University. 2 Department of Civil Engineering, University of Manitoba.

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List of Participants

Dr Hassan Aboughalma Institute of Environmental Technology, FHOOW Emden, Germany e-mail: [email protected] Ms. Anna Abyzova Geological Faculty of MSU Moscow, Russia e-mail: [email protected] Mr. Kieran Agnew School of the Environment, Civil Engineering Division, University of Brighton Brighton, UK Prof. Djamal E. Akretche U.S.T.H.B. Algiers, Algeria e-mail: [email protected] Ms. Teresa Alcántara López University of Vigo Vigo, Spain e-mail: [email protected] Mr. Ahmet Altin Zonguldak Karaelmas University Zonguldak, Turkey e-mail: [email protected] Mr. Tobias Augenstein Water Technology Center Karlsruhe, Germany e-mail: Mr. Jeong-Hyo Bae Korea Electrotechnology Research Institute Korea e-mail: [email protected] A. Prof. Kitae Baek Kumoh National Institute of Technology Gumi, Korea e-mail: [email protected] Ms. María Barreiro Miranda University of Vigo Vigo, Spain e-mail: [email protected]

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Mr. Dirk Becker DECHEMA, Karl-Winnacker-Institut Frankfurt, Germany e-mail: [email protected] Miss Ran Bi University of Applied Sciences (FHOOW) Emden, Germany e-mail: [email protected] Mr. Claudio Cameselle Fernández University of Vigo Vigo, Spain e-mail: [email protected] Dr. Henry Cardenas Louisiana Tech University Ruston, LA, USA e-mail: [email protected] Mr. Jeong-Hee Choi Korea Electrotechnology Research Institute Korea e-mail: [email protected] Mr. Jong-Young Choi Korea Advanced Institute of Science and Technology (KAIST) Daejeon, Korea e-mail: [email protected] Dr. Mohamed M. I. Darwish Shell International E&P Rijswijk, The Netherlands e-mail: [email protected] Mr. Francisco Javier Deive Herva University of Vigo Vigo, Spain e-mail: [email protected] Ms. Belen Díaz Fernández E.T.S.E.I. Universidad de Vigo Spain e-mail: [email protected] Dr. Maria Elektorowicz Concordia University Montreal, QC, Canada e-mail: [email protected] Ms. Celia Ferreira Escola Superior Agrária Coimbra, Portugal e-mail: [email protected]

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Dr. Violetta Ferri Ferrara University Ferrara, Italy e-mail: [email protected] Dr. Rafael A. García-Delgado Instituto Geológico y Minero de España (IGME) Madrid, Spain e-mail: [email protected] Mr. David B. Gent USACE Engineer Research and Development Center Vicksburg, MS, USA e-mail: [email protected] Mr. José Gómez Sieiro University of Vigo Vigo, Spain e-mail: [email protected] Ms. Susana Gouveia University of Vigo Vigo, Spain e-mail: [email protected] Mr. Yoon-Cheol Ha Korea Electrotechnology Research Institute Korea e-mail: [email protected] Dr. Boualem Hamdi U.S.T.H.B. Algiers, Algeria Prof. Jung-Geun Han Chung-Ang University Seoul, Korea e-mail: [email protected] Dr. Anne Hansen Churngold Remediation Limited Bristol, UK e-mail: [email protected] Dr. Henrik K. Hansen Universidad Técnica Federico Santa María Valparaiso, Chile e-mail: [email protected] Dr. Laurence Hopkinson University of Brighton Brighton, UK e-mail: [email protected]

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Mr. Arístides Huerga Vázquez University of Vigo Vigo, Spain e-mail: [email protected] Ms. Pernille E. Jensen Technical University of Denmark Lyngby, Denmark e-mail: [email protected] Mr. Do-Hyung Kim Kumoh National Institute of Technology Gumi, Korea e-mail: [email protected] Dr. Jae-Young Lee Korea Railroad Research Institute (KRRI) Uiwang, Korea e-mail: [email protected] Dr. MyungHo Lee Hanyang University Seoul, Korea e-mail: [email protected] Mr. You-Jin Lee Korea Advanced Institute of Science and Technology Daejeon, Korea e-mail: [email protected] Dr. Christina Liaki University of Birmingham Birmingham, UK e-mail: [email protected] Ms. Ana T. Lima Universidade Nova de Lisboa Caparica, Portugal e-mail: [email protected] Ms. Mª Carmen Lobo Bedmar IMIDRA Madrid, Spain e-mail: [email protected] Dr. J.P. Gustav Loch Utrecht University The Netherlands e-mail: [email protected] Ms. Svenja T. Lohner Water Technology Center Karlsruhe, Germany e-mail: [email protected]

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Dr. Rod Lynch Cambridge University Cambridge, UK e-mail: [email protected] Ms. Hannes Menapace University of Leoben Leoben, Austria e-mail: [email protected] Dr. Heidi Mikkola University of Leoben Leoben, Austria e-mail: [email protected] Ms. Fátima Moscoso Díaz University of Vigo Vigo, Spain e-mail: [email protected] Ms. Ana M. Nieto Castillo Instituto Geológico y Minero de España (IGME) Madrid, Spain e-mail: [email protected] Mr. Patricio Nuñez Universidad Técnica Federico Santa María Valparaiso, Chile e-mail: [email protected] Ms. Anshy Oonnittan University of Kuopio Mikkeli, Finland e-mail: [email protected] Ms. Lisbeth Ottosen Technical University of Denmark Lyngby, Denmark e-mail: [email protected] Ms. Marta Pazos Currás University of Vigo Vigo, Spain e-mail: [email protected] Prof. Krishna R. Reddy University of Illinois at Chicago Chicago, Illinois, USA e-mail: [email protected] Miss Jo Reeve Cambridge University Cambridge, UK

xii

Ms. María Teresa Ricart Ricart University of Vigo Vigo, Spain e-mail: [email protected] Ms. María Rivera Sobrado University of Vigo Vigo, Spain e-mail: [email protected] Prof. José Miguel Rodríguez-Maroto University of Málaga Málaga, Spain e-mail: [email protected] Prof. Christopher Rogers University of Birmingham Birmingham, UK e-mail: [email protected] Mr. Adrián Rojo Universidad Técnica Federico Santa María Valparaiso, Chile e-mail: [email protected] Ing. Valeria Silvia Sala Snamprogetti S.p.A. Milano, Italy e-mail: [email protected] Prof. Mª Angeles Sanromán Braga University of Vigo Vigo, Spain e-mail: [email protected] Ms. Lei Shi UFZ Helmholtz-Center for Environmental Research Leipzig, Germany e-mail: [email protected] Mr. Mika Sillanpää University of Kuopio Mikkeli, Finland e-mail: [email protected] Dr. Hagen Steger University of Karlsruhe Karlsruhe, Germany e-mail: [email protected] Ing. Giombattista Traina Istituto Giordano S.p.A. Bellaria, Italy e-mail: [email protected]

xiii

Dr. Dilek Turer Hacettepe University Ankara, Turkey e-mail: [email protected] Dr. Mario V. Vázquez University of Antioquia Medellín, Colombia e-mail: [email protected] Ms. Iria Vazquez Rodríguez University of Vigo Vigo, Spain e-mail: [email protected] Mr. Wolfgang Wesner Echem Wiener Neustadt, Austria e-mail: [email protected] Dr. Lukas Wick UFZ Helmholtz-Center for Environmental Research Leipzig, Germany e-mail: [email protected] Mr. J. Kenneth Wittle Electropetroleum Inc Wayne, PA, USA e-mail: [email protected] Prof. Gordon C. C. Yang National Sun Yat-Sen University Kaohsiung, Taiwan e-mail: [email protected] Prof. Ji-Won Yang Korea Advanced Institute of Science and Technology Daejeon, Korea e-mail: [email protected] Dr. Hans Zijlstra University of Cagliari Cagliari, Italy Dr. Roman Zorn EIfER, Karlsruhe University Karlsruhe, Germany e-mail: [email protected]

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INDEX

Plenary Lectures PL1 Sustainable soil remediation. The use of combined technologies.

Lobo, M.C, ...........................................................................................................................3

PL2 Utilization of electromigration in civil and environmental engineering. Lisbeth M. Ottosen, Iben V. Christensen, Inge Rörig-Dalgård, Pernille E. Jensen.............5

PL3 Electrokinetic delivery of nanoscale iron particles for remediation of pentachlorophenol in clayey soil. Krishna R. Reddy, Amid P. Khodadoust and Madhusudhana R. Karri ...............................7

PL4 Electroremediation – Where do we go now? Henrik K. Hansen ................................................................................................................9

Oral Presentations Session 1: Electrokinetic Barriers

S11 In-situ electrokinetic permeable reactive barrier: field investigation in the vicinity of unregulated landfill site. MyungHo Lee and Ha-Ik Chung........................................................................................13

S12 Chromate adsorbtion in a transformed red mud permeable reactive barrier using electrokinesis. Giorgia De Gioannis, Aldo Muntoni, Romano Ruggeri, Hans Zijlstra and Matteo Floris ..................................................................................................................................15

S13 Electrokinetic permeable reactive barrier for the removal of heavy metal and organic substance in contaminated soil and groundwater. Ha Ik Chung, Yong Soo Lee..............................................................................................17

S14 Use of a pulsed electric field for resisting groundwater pollution. J Reeve and R J Lynch .....................................................................................................19

Session 2: Metal Removal

S21 Phosphation of bottom-ash from MSWI by means of electrokinetics. G. Traina, S. Ferro, A. De Battisti......................................................................................23

S22 Electrodialytic removal of toxic elements from sediments of eutrophic fresh waters. Pernille E. Jensen, Lisbeth M. Ottosen, Arne Villumsen...................................................25

S23 Enhanced electrokinetic treatment of different marine sediments contaminated by heavy metals. De Gioannis Giorgia, Muntoni Aldo, Polettini Alessandra, Pomi Raffaella .......................27

S24 Electroremediation of an industrial area contaminated by chromium. O. Merdoud and D. E. Akretche ........................................................................................29

S25 Bench scale evaluation of hexavalent chromium reduction and containment using firs (ferric iron remediation and stabilisation) technology. Anne Hansen, Laurence Hopkinson, Andrew Cundy, Ross Pollock.................................31

Session 3: New Applications – Inorganic Pollutants

S31 Delivery and activation of nano-iron by DC electric field. Sibel Pamukcu, Laura Hannum, J.Kenneth Wittle ............................................................35

S32 Electro-reclamation of cyanide, impossibility or opportunity? Bas Godschalk, Wiebe Pool..............................................................................................37

xv

INDEX

S33 Electrokinetically enhanced removal and degradation of nitrate in the subsurface using nanosized Pd/Fe slurry. Gordon C. C. Yang, Chih-Hsiung Hung, Hsiu-Chuan Tu ................................................. 39

S34 Spent caustic oxidation using electrogenerated Fenton’s reagent in a batch reactor. Henrik Hansen, Patricio Nuñez, Nicolás Rodríguez......................................................... 41

S35 Physicochemical study of clay soil using inert and steel electrodes. C. Liaki, C.D.F. Rogers and D.I. Boardman ..................................................................... 43

S36 Microstructural changes in a cementitious membrane due to the application of an electrical field. A. Covelo, B. Díaz, L. Freire, X. R. Nóvoa, M. C. Pérez .................................................. 45

S37 Effect of the electrolysis time in the movement of nitrates in an andisol of Antioquía (Colombia). Diego A. Vasco, Felipe Hernández-Luis, Carmen D. Arbelo, Mario V. Vázquez ............. 47

S38 Comparative cost analysis of the electro-Fenton and the photoelectro-Fenton processes. Ahmet Altin, Eyüp Atmaca, Süreyya Altin, Vural Evren.................................................... 49

Session 4: New Applications – Bioremediation

S41 Assessment of electrode materials for an integrated bio-electro-process. Lohner S.T., Becker D., Schell H., Augenstein T., Weidlich C. ........................................ 53

S42 Electrokinetic transport and processing of bone repair agents. Henry E. Cardenas, Satya S.Vasam, Yu Zhao, Deepika Morishetti................................. 55

S43 Electro-bioremediation: influence of direct current on the physiology and dispersion of pollutant degrading bacteria in model soil. Lei Shi, Susann Müller, Hauke Harms, Lukas Y. Wick..................................................... 57

S44 Electrokinetic remediation of biosolids through inactivation of Clostridium perfringens spores. Maria Elektorowicz, Elham Safaei, Jan Oleszkiewicz, Robert Reimers........................... 59

S45 Electrokinetic enhancement of phytoremediation in Zn, Cd, Cu and Pb contaminated soil using potato plants. R. Bi, H. Aboughalma, M. Schlaak ................................................................................... 61

S46 Tetrachloroethylene bioremediation by electrochemical injection of an electron donor. Xingzhi Wu, David B.Gent, Akram Alshawabkeh Jeffrey L. Davis ................................... 63

Session 5: Organic Pollutants

S51 Influence of electroosmotic flow on the PAH release from model soil matrices. Lei Shi, Hauke Harms, Lukas Wick .................................................................................. 67

S52 Electrokinetic removal of molinate from soils: experimental and modeling. A. B. Ribeiro, J. S. Santos, E. P. Mateus, J. M. Rodríguez-Maroto, M. D. R. Gomes da Silva, L. M. Ottosen ..................................................................................................... 69

S53 Remediation of hexachlorobenzene in soil by enhanced electrokinetic Fenton process. Oonnittan, A., Shrestha, R., Sillanpää, M......................................................................... 71

S54 Integrated electrokinetic process with BDD electrode for degradation of phenol from contaminated soil. You-Jin Lee, Jong-Young Choi, Ji-Won Yang.................................................................. 73

S55 Electrokinetic remediation of the oil-contaminated soils. V. A. Korolev, O.V. Romanyukha & A.M. Abyzova........................................................... 75

xvi

INDEX

Session 6: Modelling and other Applications

S61 Prediction of the performance of EKR based on speciation analysis and mathematical modeling. C. Vereda-Alonso, A. García-Rubio, C. Gómez-Lahoz, J. M. Rodríguez-Maroto and F. García-Herruzo..............................................................................................................79

S62 Electrokinetic remediation model: electric resistivity heating with dc electric fields. Zorn, R., & Steger, H. ........................................................................................................81

S63 Strengthening of soft clay with electrokinetic stabilization method. Dilek Turer, Ayten Genc ....................................................................................................83

S64 Induced electrical gradients by hyperfiltration in clays. J.P. Gustav Loch and Katja Heister ..................................................................................85

Session 7: Electrokinetic and Electrochemical Degradation

S71 Electrochemical treatment of pharmaceutical wastewater by combining electrochemical oxidation with ozonation. Menapace, Hannes; Díaz, Nicolás ....................................................................................89

S72 Soil remediation by electro synthesis of oxidants and their electrokinetic distribution. Heidi Mikkola, Wolfgang Wesner, Julia Schmale, Slagjana Petkovska ............................91

S73 On site and in situ production of oxidants for soil remediation. W. Wesner, A. Diamant, B. Schrammel, M. Unterberger, H. Mikkola...............................93

Posters P01 Electrokinetic dewatering and remediation of river dredged contaminated high water

sediments. Ha Ik Chung, Jun Yu .........................................................................................................97

P02 Electrokinetic ultrasonic remediation of contaminated admixed soils with various clay and sand contents. Ha Ik Chung, Masashi Kamon...........................................................................................99

P03 The use of an airlift reactor with in-situ electrogeneration of Fenton´s reagent in the treatment of spent caustic from a petroleum refinery. Patricio Nuñez, Henrik K. Hansen, Jaime Guzman ........................................................101

P04 Arsenic removal from copper smelter wastewater by electrocoagulation in an airlift reactor. Henrik K. Hansen, Patricio Nuñez, Sandra Aguirre, Alejandro Jeria, Cesar Jil ..............103

P05 Integrated electrokinetic remediation technologies: opportunities and challenges. Krishna R. Reddy, Ph.D., P.E. ........................................................................................105

P06 Electrokinetic nutrient transport to stimulate microbial contaminant degradation in sandy soils. Lohner S.T., Katzoreck D., Augenstein T., Schell H., Tiehm A.......................................107

P07 A new electrode backfill material for electrokinetic soil remediation. Steger, H., Zorn, R. .........................................................................................................109

P08 Electrolytic generation of an alkaline barrier for in-situ degradation of munition constituent (RDX) contaminated groundwater. David B. Gent, Akram Alshawabkeh, Jeffrey L. Davis ....................................................111

P09 Drying brick masonry by electroosmosis – Small pilot plant. Lisbeth M. Ottosen, Inge Rörig-Dalgård..........................................................................113

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INDEX

P10 Electrokinetic settling & sedimentation behaviour of cohesive soil in dilute suspension. MyungHo Lee, Dae-Ho Kim, Soo Sam Kim.................................................................... 115

P11 Corrosion remediation using chloride extraction concurrent with electrokinetic pozzolan deposition in concrete. Henry E. Cardenas, Kunal Kupwade-Patil...................................................................... 117

P12 Electrokinetic treatment for freezing and thawing damage remediation within limestone. Henry E. Cardenas, Pradeep Paturi ............................................................................... 118

P13 Remediation of oil-polluted soils by the electrochemical lixiviation. V. A. Korolev & O.V. Romanyukha................................................................................. 119

P14 Assessment of electrokinetic metal removal from biosolids. Elektorowicz Maria, Hadhir Aboli, Jan A. Oleszkiewicz.................................................. 121

P15 Electrokinetic removal of bentazone from soils: experimental and modeling. A. B. Ribeiro, C. S. Abreu, E. P. Mateus, J. M. Rodríguez-Maroto, M. D. R. Gomes da Silva, H. K. Hansen.................................................................................................... 122

P16 Electrochemical degradation of PAHs from water in the presence of surfactants. T. Alcántara, J. Gómez, M. Pazos, S. Gouveia, C. Cameselle and M. A. Sanromán.... 123

P17 Electrokinetic remediation of benzo[a]pyrene from contaminated kaolinite. J. Gómez, T. Alcántara, M. Pazos, C. Cameselle and M. A. Sanromán........................ 125

P18 Electrokinetic remediation and electrochemical treatment of dye polluted kaolinite. M. Pazos, C. Cameselle and M. A. Sanromán............................................................... 127

P19 Removal of organic pollutants and heavy metals in soils by electrokinetic remediation. M.T. Ricart, M. Pazos, S. Gouveia, C. Cameselle and M.A. Sanromán ........................ 129

P20 Electrokinetic desorption processes of soft soil contaminated with heavy metal. MyungHo Lee, Jung-Geun Han and Jai-Young Lee ...................................................... 131

P21 Electrokinetic bleaching of kaolin clay. C. Cameselle, M. Pazos, I. Vazquez, F. Moscoso and M. A. Sanromán ....................... 133

P22 Electromigration of Mn, Fe, Cu and Zn with citric acid in polluted clay. M. Pazos, A. Huerga, J. L. Prieto, S. Gouveia, M. A. Sanromán, C. Cameselle ........... 135

P23 Electrodialytic remediation of suspended mine tailings. Henrik K. Hansen, Adrian Rojo, Lisbeth M. Ottosen, Alexandra Ribeiro ....................... 137

P24 Electrodialytic remediation of copper mine tailings using bipolar electrodes. Adrián Rojo, Henrik K. Hansen....................................................................................... 139

P25 Enhanced electrokinetic soil remediation of heavy metals. Ayten Genc, George Chase............................................................................................ 141

P26 Preliminary treatment of MSW fly ash as a way of improving electrodialytic remediation. Célia Ferreira, Lisbeth Ottosen, Alexandra Ribeiro........................................................ 143

P27 An enhanced electrokinetic remediation for lead removal from soils polluted from a zinc production plant. Ahmet Altin, Mustafa Degirmenci ................................................................................... 145

P28 Electrolyte conditioning for electrokinetic remediation of arsenic from mine tailing. Do-Hyung Kim, Byung-Gon Ryu, Sung-Woo Park, Jung-Seok Yang, Kitae Baek......... 147

P29 Anolyte conditioning-enhanced electrokinetic remediation of fluorine-contaminated soil. Do-Hyung Kim, Kitae Baek, Sung-Hwan Ko................................................................... 149

xviii

INDEX

P30 Electrokinetic remediation of Ni and Zn contaminated soil: catholyte conditioning. Do-Hyung Kim, Hyun-Duck Choi, Min-Chul Shin, Chil-Sung Jeon, Kitae Baek..............151

P31 Straw ash – Electrodialytic removal of Cd in a pilot scale. A. T. Lima; Ottosen, L.M.; Ribeiro, A.B.; H.K. Hansen....................................................153

P32 Electrokinetic remediation of metal and surfactant from sewage sludge. Violetta Ferri, Sergio Ferro, Claudio Anzalone, Achille De Battisti .................................155

P33 Dialytic and electrodialytic removal of heavy metals from MSW fly ash: experimental and modeling. A. T. Lima, A. B. Ribeiro, J. M. Rodríguez-Maroto, A. Varela-Castro, L. M. Ottosen .....157

P34 Electrochemical re-impregnation of wood with copper. Iben V. Christensen, Lisbeth M. Ottosen, Simon R. Jensen; Morten B. Jacobsen.........159

P35 Transport of boron in wood - an electrokinetic accelerated wood impregnation process. Iben V. Christensen, Lisbeth M. Ottosen, Inge Rörig-Dalsgaard ....................................161

P36 Remediation of a chromium (VI) contaminated soil by electrodialysis. Ana M. Nieto Castillo, Juan J. Soriano, Rafael A. García-Delgado ................................163

P37 A simple computer model for the electrodialytic remediation of a chromium (VI) contaminated soil. Rafael A. García-Delgado ,Ana M. Nieto Castillo, Juan J. Soriano ................................165

P38 Implementation of a iodide enhanced EKR to a mercury contaminated soil. A. García-Rubio, J. M. Rodríguez-Maroto, F. García-Herruzo, C. Vereda-Alonso, C. Gómez-Lahoz, J. M. Esbrí and P. Higuera.................................................................167

P39 Electrokinetic remediation of a radionuclid- contaminated soils. V. A. Korolev, Y.E. Barkhatova, E.V. Shevtsova.............................................................169

P40 Electrokinetic remediation of a soil contaminated with heavy metals in a scale pilot experiment. Lobo, M.C, Martinez-Iñigo, M.J, Pérez-Sanz, A, Plaza, A, Alonso, J, Perucha, C .........171

P41 Electrokinetic remediation of metal-contaminated soil. Larisa L.Lysenko, Nataliya A.Mishchuk...........................................................................173

P42 Electrokinetic remediation of copper contaminated clay soils. Nataliya Mishchuk, Larysa Lysenko, Boris Kornilovich ...................................................174

P43 Fundamental problems of soil and sludge decontamination by application of an electric field. Nataliya A. Mishchuk .......................................................................................................175

P44 Remediation of cadmium contaminated paddy soils by washing with calcium chloride in Pindi-Bhatian (Punjab) Pakistan. Tahir Mehmood, Syed Tasawar Abbas, Kashif Shahbaz and Muhammad Bashir .........177

P45 Comparative leaching reagent effects in the course of an electroremediation of a soil contaminated by lead. S. Amrate, B. Hamdi, D. E. Akretche, M. Pazos, C. Cameselle and C. Innocent ...........179

P46 From electroremediation to metal valorisation. N. Sabba and D. E. Akretche ..........................................................................................181

xix

Plenary Lectures

6th Symposium on Electrokinetic Remediation Plenary Lecture EREM 2007 PL1

SUSTAINABLE SOIL REMEDIATION. THE USE OF COMBINED

TECHNOLOGIES. Lobo, M.C. Instituto Madrileño de Investigación y Desarrollo Rural Agrario y Alimentario. IMIDRA. A-2, Km 38,2 28800 Alcalá de Henares (Madrid). Spain. Tel: 34 918879472 fax: 34 91 889474. E-mail: [email protected] Soil contamination has been identified as a threat in the proposal for a Directive for Soil Protection, presented to the European Parliament (COM, (2006), 232), due to the impact of the local and diffuses sources on the soil During the last decades, different soil remediation technologies have been studied and applied depending on type and content of pollutant, soil characteristics and future use of the contaminated site. The best technology must be a permanent solution, applied in situ and safe for the human health. Electrokinetic technologies seem to be an adequate alternative to remove pollutants from the soil. Their advantages are: low cost, non-intrusive character, applicability to a wide range of contaminants and insensitivity to pore size soil that makes it suitable for fine-grained soils. (Acar, Y.B and Alshawabkeh, 1993, Reddy et al., 2002) However, previous assays have shown a direct relationship between removal efficiency and soil characteristics, as particle size, pH and organic matter and carbonate content. Ionic mobility is depending on pH, therefore purging solution with different ionic strength are necessary in order to mobilize and remove pollutants in different soils. (Ugaz et al. 1994, Saichek and Reddy, 2003). Water and citric acid have been used by several authors to mobilize pollutants. Nevertheless, if they are strongly fixed to the soil constituent, it is necessary to use another solvent to increase pollutants mobilization, as acids or quelant agents (Kim et al., 2001, Zhou et al., 2003), which can affect soil dynamic. Recently, polarity exchange technique has been used to increase the pollutant solubization and consequently the metal removal (Pazos et al., 2006). Besides, electrochemical electrode reactions, electroosmosis and electromigration due to the electrokinetic technology application cause different process in the soil as: solution, precipitation, redox reactions, changing of surface potential of soil particles, destroying of clay mineral under acid conditions as well as exchanging of ions.(Acar et al, 1995, Page and Page, 2002). These variable conditions can produce changes in soil structure, and consequently the soil physicochemical parameter could be modified. The diversity of pollutants (heavy metals and organic compounds) and soils require to consider each polluted site as a particular site. Due to the importance of minimizing the impact of this technology application, from the point of view of the future use of the soil, the use of combined technologies could constitutes a suitable strategy for soil remediation. Biological technologies are sustainable for soil conservation, but their application is conditioned to the level of pollutants. These technologies could be used in a second step after electrokinetic process or even during the process in order to enhance the mobilization and removing of pollutants. Microorganisms are able to biodegradate organic compounds (Alef and Nannipieri, 1995, Willaert, 1996, Martin et al., 2000, Lobo et al., 2003) and solubilize heavy metals (bioleaching) (Brombacher et al., 1998, Kaibitz and Wenrich, 1998, Gadd, 2000) This fact could improve the mobilization of ionic charge towards the electrodes.

3

Some plants with tolerance to heavy metals could be used to remove these pollutants from soil, when the application of the electrokinetic technologies doesn’t allow the total removal. Even, bioremediation and phytoremediation can be enhanced by the effect of the direct current on the soil (Acar et al., 1996, Maini et al., 2000, O´Connor et al., 2003, Both remediation strategies, biological and electrokinetic, could be used in combination, but more effort must be done in field conditions, in order to demonstrate their efficency, evaluating the impact on the soil. Ecotoxicological assays must be carried out during and after the remediation process to assess the environmental impact on the ecosystem. References:

Alef, K. and Nannipieri, P. 1995. Methods in Applied Soil Microbiology and Biochemistry. Academic Press, London Acar, Y.B and Alshawabkeh, A.N., 1993. Principles of Electrokinetic Remediation. Enviornmental Science and Technology. Vol 27. Nº 13, 2638-2647. Brombacher, C, Bachofen, and R, Brandl, H. 1998. Development of a Laboratory Scale leaching plant for metal extraction from fly ash by Thiobacillus Strains. Applied and Environmental Microbiology. 64 (4), 1237-1241. Comission of the European Communities. COM. 2006, 232. Proposal for a Directive of the European Parliament and of the Council. http://ec.europa.eu/comm/environment/soil/index.htm Gadd, G. M. 2000. Bioremedial potential of microbial mechanism of metal mobilization and inmobilization. Current Opinion in Biotechnology. 11, 271-279. Kalbitz, K and Wenrich, R. 1998. Mobilization of heavy metals and arsenic in polluted wetland spills and its dependence of dissolved organic matter. The Science of the Total Environment. 209. 27-39. Kim, S, Moon, SH, and Kim, K.W. 2001. Removal of heavy metals from soils using enhanced electrokinetic soil processing. Water, Air, Soil Pollut. 125 (1-4). 259-272. Lobo, M.C, Sanchez, M, Garbi, C, Ferrer, E, Martinez Iñigo, M.J, Allende, J.L, Martín, C, Casasus, L, Alonso-Sanz, R, Gibello, A and Martín, M. 2003. Bioremediation of soils and waters by using inmobilized native bacteria :implementation and modeling. Water, Air & Soil: Focus, 3(3)35-46. 2003 Maini, G, Sharman, AK, Sunderland, G, Knowles, CJ, and Jackman, S.A. 2000. An integrated method incorporating sulphur-oxidizing bacteria and electrokinetic to enhance removal of copper from contaminated soil. Environm. Sci. Technol. 34 (6). 1081-1087. .Martin, M. Mengs, G. Garbi, M. Sánchez, A. Gibello, F. Gutierrez, and E. Ferrer. (2000). Propachlor removal by pseudomonas strain GCH1 in an inmobilixzed cell system. Applied Envriron, Microbiol., 66, 3, 1190-1194 O´Connor, CS, Lepp, NW, Edwards, S.R., Sunderland, G. 2003. The combined use of electrokinetic remediation and phytoremdiation to decontaminate metal-polluted soils: a laboratory-scale feasibility study. Environm. Monitor. Assess. 84 (1-2) 141-148. Page, MM. and Page, CL. 2002. Electroremediation fo contaminated soil J. Environm. Eng. 128. (3).208-219. Pazos, M; Sanroman, MA and Cameselle, C. 2006. Improvement in the electrokinetic remediation of heavy metals spiked caolin with the polarity inversion technique. Chemosphere. 62 (5) 819-822. Reddy, K.R, Saichek, R.E, Maturi, K and Ala, P, 2002. Effects of soil moisture and heavy metals concentrations on electrokinetic remediation. Indian Geotechnical Journal. 32 (2). Saichek, RE, and Reddy, KR. 2003. Effect of pH control at the anode or the electrokinetic removal of phenanthrene from kaolin. Chenosphere. 51. 273-287. Ugaz, A, Puppah, S, Gale, R.J, and Acar, YB. 1994. Electrokinetic soil processing. Complicating features of elecgtrokinetic remediation of soils and slurries: saturation effects and the role of the cathode electrolysis. Chem. Eng. Commm. 129. 183-200. Willaert, R. G., Baron, G. V, and De Backer, L. 1996. Inmobilised Living Cell Systems. Wiley and Sons, Sussex Zhou, DH, Zorn, and R, Kurt, C. 2003. Electrochemical remediation of copper contaminated kaolinite boy conditioning analyte and catholyte pH simultaneously. J. Environ. Science-China. 15 (3). 396- 400.

4


UTILIZATION OF ELECTROMIGRATION IN CIVIL AND ENVIRONMENTAL ENGINEERING

Lisbeth M. Ottosen, Iben V. Christensen, Inge Rörig-Dalgård, Pernille E. Jensen Department of Civil Engineering, Building 118, Technical University of Denmark, 2800 Lyngby, Denmark E-mail: [email protected] Moist porous media are ionic conductors and applied current flows as a result of the movement of dissolved ions in the pore solution (electromigration). The pores walls have unbalanced charges and corresponding unbound ions, and the electric current can be carried by ions lining the surface of the pores and by the ions dissolved in the free water phase, with rather different characteristics. Electromigration of ions can be obtained even in fine grained/pored materials and is utilized to remove or supply ions into porous matrixes in both of civil and environmental engineering. Eventhough there are many topics within electrokinetics of common interest for these two fields of engineering there is no tradition for collaboration. The present work outlines the various processes and materials where electromigration has been suggested (or are) used together with the purpose of the process and the best results obtained is summarised. Scientific focus is laid on changes in the porous matrix and pore solution due to the applied electric field where knowledge from the two fields is combined and discussed. The overall aim is to identify areas for future collaboration. The work is based on a literature survey as well as own experiments. Civil engineering. Utilization of electromigration in civil engineering is mainly for repair and maintenance purposes. The methods are far most developed for concrete, however, also in brick masonry and wood, electromigration can be advantageous.

• Removal of chloride from concrete, designed for situations where reinforcement corrosion has started due to ingress of chloride.

• Realkalization of concrete is used for carbonated reinforced concrete structures and entails the re-establishment of alkalinity around the reinforcement and in the cover zone

• Crack closure in concrete by deposition for filling the cracks and to coat the surface by with compounds as CaCO3 and Mg(OH)2.

• Re-impregnation of wood in structures. Transport of boron or copper into wood in structures of e.g. heritage buildings, to hinder decay.

• Removal of salts from brick masonry suffering from salt weathering caused by high salt concentrations.

• Electrokinetic stabilization is a ground improvement method for soft soils. With this method, stabilizing agents are injected into the soils to achieve stabilization by means of ion exchange, precipitation or mineralization.

Environmental engineering. Electromigration is mainly used for transporting pollutants out from contaminated matrices and here soil is the most investigated material, but also the transport of ions into the matrices can be of value in some situations.

• Removal of heavy metals. Such processes have shown successful for remediation of different materials such as soil, sediment, fly ash, waste water sludge and waste wood.

• Removal of salt (NaCl) from soil to improve the quality of saline-sodic soils to hinder land degradation

• Improved bio-remediation organic soil pollutants. There are different ways electromigration can improve the conditions for the microorganisms e.g. supplying surfactants or increase bioavailability of the pollutant.

5

There is no doubt from the experiences obtained with the above mentioned processes that electromigration is a powerful tool to remove ions, supply ions or to change chemical conditions in porous media – even very fine porous media where other processes based on e.g. pressure gradients fails. It could certainly be advantageous to share knowledge and know how obtained in the two fields of electrokinetics, both in order to increase the understanding of electrokinetics in various porous media and the effect that can be expected on the porous media itself, but there are also situations where direct collaboration is necessary. Further also some subjects within construction of electrodes and control of the process could be beneficial to share. An example where collaboration is necessary is a situation where electrokinetic soil remediation is planned under a house. In such action it is of crucial importance to the environmental engineer to know how/if the building materials is influenced by the applied electric field. Another situation could be electrokinetic salt removal from a basement wall where one of the electrodes is placed in the soil outside the building. Here knowledge on electrokinetics in soil is important to the civil engineer. The issue of pH changes from the electrode processes is a common key issue. An alkaline and an acidic front develop from the cathode and anode, respectively, if no precautions taken. Acidification from the anode is aiding heavy metal release and is thus very important in remediation of e.g. soil and sediments but the alkaline front prevents full remediation due to precipitation of the heavy metals. Concrete has a natural high pH and it is very important to avoid acidification since concrete is destroyed by acidification. The alkaline front in concrete, on the other hand, is only of concern because the transference number of Cl- decreases due to competition with OH-. Combining the fields of soil remediation and chloride removal from concrete, know how is available on possible electrode constructions that can hinder pH changes in the porous matrix, which is necessary in e.g. re-impregnation and beneficial when removing salts from masonry. An important issue to every process that involves applying an electric DC field to a porous media is transport of non-target ions and matrix changes. In every process it is necessary to know the properties of the matrix after the treatment, either to find use of the material (e.g. fly ash or sediment) or to be certain that the materials properties have not been changed unacceptably (e.g. wood, concrete or bricks). It is certain, that the applied electric field is not only transporting the target ions out from the matrix (or into). Non-target ions are also transported, and non-target ions of interest in most matrices are e.g. Ca, K and Na. These are common soil elements and it has been shown, that these elements are removed during electrokinetic soil remediation which is of no concern except for the current wasted in transporting these ions. When treating straw ash from biomass combustion the removal of K is unwanted since K is adding significantly to the fertilizer value of the remediated ash. In concrete, on the other hand, the transport of Na and K can be a limitation to the process due to the danger of alkali-kisel reaction. The literature survey has surely underlined that it could be beneficial to collaborate and exchange knowledge of electrokinetics within the two fields civil and environmental engineering in order to raise the common understanding of the processes.

6


ELECTROKINETIC DELIVERY OF NANOSCALE IRON PARTICLES FOR REMEDIATION OF PENTACHLOROPHENOL

IN CLAYEY SOIL Krishna R. Reddy1, Amid P. Khodadoust2, and Madhusudhana R. Karri3

1Professor, 2Associate Professor and 3Graduate Research Assistant University of Illinois at Chicago, 842 West Taylor Street, Chicago, Illinois 60607, USA Tel: 312-996-4755; Fax: 312-996-2426; E-mail: [email protected] Several researchers have synthesized different types of nanomaterials for a wide range of engineering applications. However, only recently nanoscale iron particles (NIPs) have received the attention of environmental professionals to remediate contaminated sites. This paper investigates: (1) the reactivity of NIPs to promote the reductive degradation of pentachlorophenol (PCP) in clayey soils, and (2) potential to deliver NIPs into PCP-contaminated clayey soils using electrokinetics and resulting PCP reduction efficiency. Kaolin was used as a model low permeability clayey soil and was artificially spiked with PCP at initial concentration of 500 mg per Kg of dry soil (mg/Kg) or 1000 mg/Kg. PCP was chosen because it is one of the common contaminants found at former wood preserving contaminated sites. To spike the soil, hexane was used to dissolve solid PCP, and this hexane-PCP mixture was slowly added to dry kaolin soil. The mixtures were stirred with stainless steel spoons within glass beakers and then placed beneath a ventilation hood for nearly a week until the hexane completely evaporated and the contaminated soil was dry. The dry soil was then mixed with 35% deionized water to simulate typical field moisture conditions. The NIPs used for this study were produced using the the patented method by Uegami et al. (US2003/0217974A1) and consisted of an elemental iron core (α-Fe) and a magnetite shell (Fe3O3) in approximately same amounts by weight. The aqueous NIP suspension with 25.6 wt.% solid concentration had density of 1.27 g/mL. The average particle size and surface area of NIPs was 70 nm (0.07 μm) and 28.8 m2/g, respectively. A series of laboratory batch experiments was conducted on PCP-contaminated kaolin with different contact time (1, 2, 8, 12, 24 and 48h) and different NIPs concentrations (1, 2, 4, 5, 8, 10, 20, 40, 60, 80 and 100 g/L) to investigate the reactivity and optimum concentration of NIPs. These experiments were conducted in 40-mL glass vials containing 25 mL of NIPs suspension of known concentration (5, 10 and 20 g/L) and 5 g of PCP spiked kaolin soil (with PCP concentration of 1000 mg/Kg). The soil-NIPs suspensions were shaken for 48 hours. The aqueous suspension was centrifuged at 4000 rpm for 30 min to separate the solids from the liquid. The supernatant and the residual soil were analyzed for PCP concentration using GC-MS. These results showed that 80 to 98% PCP was removed from the soil within an hour, but PCP reduction was increased from 50 to 78% at 1h to 40 to 90% at 24 h reaction time for different NIP concentrations. There was no significant effect of NIPs concentration on the PCP removal, but the amount of PCP reduction increased with increase concentration of NIPs with 30% at 1 g/L to 98% at 100 g/L. There appears to be an optimal NIPs concentration beyond which benefits are diminished. A series of electrokinetic experiments was conducted to investigate electrokinetic delivery of NIPs and resulting PCP reduction efficiency. The testing equipment and the procedure were the same as that used in previous studies at University of Illinois at Chicago (UIC). Kaolin spiked with PCP with an initial concentration of 500 mg/Kg was tested under different NIP concentrations, voltage gradients, operating duration, and enhancement

7

conditions as summarized in Table 1. Except for the control test, the anode reservoir was filled with NIPs suspension and recirculated with a pump, while the cathode reservoir was filled with deionized water. During the application of electric potential, current and the electroosmotic flow were recorded. At the end of each test, aqueous samples from the electrodes and dissected soil sections were analyzed for pH, iron and PCP.

Table 1. Testing Program to Investigate Electrokinetic Delivery of NIPs

Test Date

Test Designation

Voltage Gradient (VDC/cm)

Anode Flushing Solution

Test Duration (Hours)

Pore Volumes

NIP0 1.0 Distilled Water 427 1.2 NIP1 1.0 5 g/L NIP 427 2.1

March 31, 2003-April 18, 2003 NIP2 1.0 10 g/L NIP 427 2.2

NIP3 2.0 5 g/L NIP 937 0.9 NIP4 2.0 10 g/L NIP 936 1.5

NIP5 1.0 0.5% Tween 80 + 5 g/L NIP 936 2.4

August 28, 2003-

October 7, 2003

NIP6 1.0 5% Ethyl Alcohol + 5 g/L NIP 936 2.5

The test results showed that the current increased rapidly during the first few hours, then decreased over a period of time. The measured electroosmotic flow varied depending on the test conditions as shown in Table 1. Very low amounts of iron and PCP were detected in the effluent. The dissected soil sections revealed that soil pH decreased in the first four sections from the anode but was the highest in the section closer to the cathode. The iron concentrations in soil increased from the anode to the cathode, indicating the delivery of NIPs into the soil using electrokinetics. Visual observations also revealed the presence of iron particles within the first two sections from the anode. A low concentration of PCP was observed in the first section away from the anode that increased up to the third section and then further decreased towards the cathode end, indicating the migration of PCP occurring from anode to cathode. The amount of PCP reduction by NIPs was calculated based on the initial mass in the soil, the mass removed in the effluent, and the mass remaining in the soil and it ranged from 100% near the anode to 5% near the cathode. The enhanced electrokinetic experiments results showed that high electroosmotic flow was obtained in the cosolvent enhanced system (2.5 pore volume) as compared to surfactant enhanced system (2.4 pore volume) resulting in the increased injection of nanoiron into the soil. Further it was also evaluated that the transport and dispersion of nanoiron particle was more uniform in surfactant enhanced system as compared to cosolvent enhanced system. Overall, the results from this study revealed that the extent of delivery and reactivity of NIPs were limited by passivation and aggregation of NIPs under the oxygenated and low pH conditions that exist at the anode as well as complex geochemical reactions occurring simultaneously at different rates. The NIPs transport may be affected by probable dissolution of substrate minerals and possible precipitation of secondary solids as well as changes in the surface charge of all solids as the solution composition changes. Parameters controlling these reactions include pH, Eh, solution composition, and solid (both NIPs and substrate) composition and structure. Besides these considerations, the system parameters such as voltage gradient, mode of voltage gradient application (pulsed versus continuous), and pH control at the anode and cathode should be optimized.

8


ELECTROREMEDIATION – WHERE DO WE GO NOW? Henrik K. Hansen Universidad Técnica Federico Santa María, Av. España 1680, Valparaiso, Chile E-mail: [email protected] About 20 years ago the first full and pilot scale electrokinetic soil remediation processes to remove heavy metals were reported [1,2]. The electrokinetic phenomenon electroosmosis together with electromigration of heavy metal ions were key factors in this remediation technique. Industry, remediation companies and academics worked together in the successful development of the remedation method. Since then only a few soil remediation companies have continued to offer electrokinetic remediation as treatment solution [3]. Why has the interest stopped? Is the method to complicated? Patent rights restrictions? Is it too expensive? Is it not efficient? Does heavy metal contaminated soil not cause sufficient risk for society? On the other hand, the research during the last 5 – 10 years in the area of electroremediation is increasing and showing that we are turning into other waste mateials such as ashes, wood waste, sewage sludge and even wastewater. Furthermore, we are combining different effects – using the electric current to enhance other remediation processes. Soil has become less important since regulatives generally is getting less strict when it comes to heavy metal contamination in soils. Only toxic organic contaminants and radioactive elements are of great concern, and researchers are turning their interest into these cases. The aim with this presentation is to start a discussion whether or not “true” electrokinetic remediation of soil still has potential and interest to be a reference remediation technology. [1] US-EPA Report 402-R-97-006 (1997). [2] Lageman, R., Environmental Science and Technology, 27 (1993) 2648-2650. [3] Lageman, R., Clarke, RL., Pool, W., Engineering Geology 77 (2005) 191-201.

9

Oral Contributions to session 1

Electrokinetic Barriers

IN-SITU ELECTROKINETIC PERMEABLE REACTIVE BARRIER: field investigation in the vicinity of unregulated landfill site

MyungHo Leea and Ha-Ik Chungb aBK Research Associate, Dept. of Civil & Environ. Eng., Hanyang Univ., South Korea E-mail: [email protected] bResearch Fellow, Geotechnical Eng. Research Dept., KICT, South Korea

ABSTRACT

This paper presents preliminary field investigations on the electrokinetic remediation coupled with permeable reactive barrier system. Unregulated and old-fashioned landfills are one of the primary contributors to various contaminated soil problems. In-situ electrokinetic remediation technology has been successfully applied to the environs of unregulated landfill site, located in Kyeong-Ki province, Korea. Atomizing slag was adopted as a PRB reactive material for the remediation of groundwater contaminated withinorganic and/or organic substances. From the preliminary investigations, the coupled technology of EK with PRB system would be effective to remediation contaminated grounds without the extraction of pollutants from subsurface due to the reactions between the reactive materials and contaminants.

Keywords: atomizing slag, clayey soil, electrokinetics, landfill, permeable reactive barrier

(a) (b)

Fig. 1. Testing apparatus for electrokinetic permeable reactive barrier system: (a) electrode array; (b) perforated electrode chamber and drainage system

(-)Sand

(-)Zeolite

(-)Atomizing Slag

(-)Fe2+

1 m

1 m

(+)Sand

< Case 1 >

< Case 2 >

Electrode Well

Vacuum Pump

Drainage Tubing

Electrode

ToPowerSupply

13

6th Symposium on Electrokinetic RemediationEREM 2007

Oral PresentationS11

(a)

(b)

Fig. 2. Contaminant concentration vs. time: (a) arsenic concentration; (b) lead concentration

[1] Acar, Y. B. and Alshawabkeh A. N. (1993), “Principles of electrokinetic remediation”, Environ. Sci. Technol., 27(13), pp. 2638-2647.

[2] Lee, M. (2007), “New concept of remediation technique for the contaminated ground and groundwater: Electrokinetic Permeable Reactive Barrier System (EKPRBS)”, Korea Society of Waste Management, 24(2), pp. 134-140. (in Korean)

[3] Melitas, N., Conklin, M. and Farrell, J. (2002), “Electrochemical study of arsenate and water reduction on iron media using for arsenic removal from potable water”, Environ. Sci. Technol., 36(14), pp. 3188-3193.

[4] Mitchell, J. K. (1993), “Fundamentals of soil behaviour”, Wiley Inter. Science [5] Morrison, S. (2003), “Performance evaluation of a permeable reactive barrier using

reaction products as tracers”, Environ. Sci. Technol., 37(10), pp. 2302-2309. [6] Simon, F. G. and Meggyes, T. (2000), “Removal of organic and inorganic pollutants

from groundwater using permeable reactive barriers: part 1. treatment processes for pollutants, Land Contamination Reclamation, Vol. 8, No. 2.

[7] Yeung, A. T. (1994), “Electrokinetic flow processes in porous media and their applications”, Advances in porous media, Elsevier, 2, pp. 309-395.

0 5 10 15 20 25 30 35 40 45 50

Time (hr)

0.00

0.02

0.04

0.06

0.08As

con

c. (m

g/L)

Electrokinetic remediation (EKR)

Electrokinetic permeable reactive barrier system (EKPRBS)

0 5 10 15 20 25 30 35 40 45 50

Time (hr)

0.0

0.2

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Oral PresentationS11

6th Symposium on Electrokinetic Remediation Oral Presentation EREM 2007 S12

CHROMATE ADSORBTION IN A TRANSFORMED RED MUD PERMEABLE REACTIVE BARRIER USING ELECTROKINESIS

Giorgia De Gioannisa, Aldo Muntonia*, Romano Ruggerib, Hans Zijlstrab and Matteo Florisa

aUniversity of Cagliari, Department of Geoengineering and Environmental Technologies, Piazza d’Armi – 09123 Cagliari, Italy; bVirotec Italia, Via Alessandria 112 00198 Roma, Italy e-mail: [email protected] Seawater neutralized Red Mud with soil neutral pH and acid neutralizing capacity of about 4 moles per kg is used in environmental remediation for treatment of acid to slightly alkaline, metal contaminated water and soil [1, 2, 3]. It has been observed that the micron sized etched mineral particles with high specific surface, containing up to 35 wt% of hematite, are excellent adsorbents for metal oxyanions such as arsenate, antimonate, and chromate. However, significant adsorption capacities of more than 1 mg/g are only observed after the seawater neutralized Red Mud is activated by acid and fluid pH is less than 6.5 [4, 5]. For treatment of metal oxyanion contaminated acid waters such conditions can be readily attained, however for metal oxyanion contaminated neutral soils, costly soil acidification or acid pre-treatment of seawater neutralized Red Mud could be required. During electrokinetic remediation of metal contaminated soil, hydrogen ions are generated at the anode and hydroxyl ions at the cathode [6, 7, 8]. Thus it is hypothesised that metal oxyanions can be removed from contaminated soil by an electric field, in order to accumulate at the oppositely charged anode, where they can be readily adsorbed on seawater neutralized Red Mud that is acid activated by the hydrogen ions produced by the anode. In order to test the hypothesis, a laboratory-scale electrochemical cell of about 30 cm length is filled with about 2 kg of clayey soil of pH 5.5 that is artificially contaminated with 1000 mg chromate per kg dry weight [9]. Subsequently, a 30 V electric field is maintained during 12 days and afterwards, the pH and chromium concentrations of 6 soil slices are assessed. As the clayey soil has a fairly high adsorption capacity for chromate due to the presence of ferrous iron and the reduction of soluble chromate to insoluble chromium III, in particular at lower pH conditions near the anode, two different setups using seawater neutralized Red Mud were investigated, and compared to an electrokinetic test with only chromate contaminated clayey soil. In the first test, a modest amount of 30 g of seawater neutralized Red Mud is mixed with the clayey soil adjacent to the anode. The quantity is chosen such that it just neutralizes the acid produced at the anode during the duration of the test. The idea is that in doing so, acidification of the soil near the anode is prevented; the hydroxyl front produced by the cathode can advance as far as possible towards the anode promoting desorbtion of the chromate; and chromate adsorption and chromate – chromium III conversion are hampered near the anode. In the second test, a considerable amount of acid activated seawater neutralized Red Mud is mixed with the clayey soil adjacent to the anode. In this case, the idea is to provide an optimum adsorbent for chromate adsorption, allowing electrokinetic removal of chromate from clayey soil, without the need of electrolyte purification and the ex-situ disposal of the recovered chromate contaminant. The latter should substantially reduce the costs of electrokinetic remediation of, for instance, metal oxyanion contaminated

15

mining waste dumps in remote mountainous areas, which are common in Sardinia that is characterized by numerous abandoned metal ore mines, exploited since Roman times. The results of both laboratory-scale tests using seawater neutralized Red Mud permeable reactive barrier in combination with electrokinetic remediation of artificially chromate contaminated clayey soil are compared to electrokinetic remediation alone and discussed with respect to the possibility of field-scale application. [1] McConchie D., Saenger P., and Fawkes R., (1996). An environmental assesment of the use of seawater to neutralise bauxite refinery wastes. In: V. Ramachandran and C.C. Nesbitt (eds.) Proceedings of the 2nd Internat. Symp. On Extraction and Processing for the Treatment and Minimisation of Wastes. The Minerals, Metals, and Materials Soc., Scottsdale Arizona, 407 – 416. [2] McConchie D., Clark M., Hanahan C. and Fawkes R. (1999) The use of seawater-neutralised bauxite refinery residues (red mud) in environmental remediation programs. IN: I. Gaballah, J. Hager and R. Solozabal (eds.) Proceedings of the 1999 Global Symposium on Recycling, Waste Treatment and Clean Technology, San Sebastian, Spain. The Minerals, Metals and Materials Society, 1: 391-400. [3] Zijlstra J.J.P., Bello V., Ruggeri R. And Teodosi A. (2005). The BAUXSOLTM Technology: An innovative solution for environmental remediation problems. In; R. Cossu and R. Stegmann (eds), Proceedings Sardinia 2005 Tenth International Waste Management and Landfill Symposium, 1019 – 1020. [4] Cenc-Fuhrmann H., Tjell J.C., and McConchie D., (2004). Adsorption of Arsenic from Water Using Activated Neutralized Red Mud. Environ. Sci. Technol., 38 (8), 2428 -2434. [5] Mureddu, M (2006). Indagini di laboratorio sulla capacità del BAUXSOLTM di migliorare la rimozione del Cromo da acque contaminate. Universita’ degli Studi di Cagliari, Facoltà di Scienze Matematiche, Fisiche e Naturali Dipartimento di Scienze Chimiche. Tesi di Laurea, 63 p. [6] Lindgren, E.R., Mattson, E.D., & Kozak, M.W. (1992). Electrokinetic remediation of unsaturated soils. In D.W. Tedder & F.G. Pohlan (Eds.), Emerging technologies in hazardous waste management IV: ACS symposium series, Atlanta, GA (pp. 33–50). [7] Mascia M., Muntoni A., Palmas S.,1, Polcaro A.M., Vacca A., 2006. Experimental study and mathematical model on remediation of Cd polluted soils by electrokinetics. Electrochimica Acta (Elsevier), (M. Mascia et al., Electrochim. Acta (2006), doi:10.1016/j.electacta.2006.04.066), Vol. 52, Issue 10, ISSN 0013-4686, febbraio 2007. [8] Lynch R.J., Muntoni A., Ruggeri R., Winfield K.C., 2006. Preliminary tests of an electrokinetic barrier to prevent heavy metal pollution of soils. Electrochimica Acta (Elsevier), Vol. 52, Issue 10, ISSN 0013-4686, doi:10.1016/j.electacta.2006.06.049, febbraio 2007. [9] Reddy, K.R., & Parupudi, U.S. (1997). Removal of chromium, nickel and cadmium from clays by in-situ electrokinetic remediation. Journal of Soil Contamination, 6(4), 391–407.

16


ELECTROKINETIC PERMEABLE REACTIVE BARRIER FOR THE REMOVAL OF HEAVY METAL AND ORGANIC SUBSTANCE IN

CONTAMINATED SOIL AND GROUNDWATER Ha Ik Chunga, Yong Soo Leeb

a Research Fellow, Korea Institute of Construction Technology, 2311 Daewha-dong Ilsan-gu Goyang-shi Gyeonggi-do, Korea, Tel +82-31-910-0216, Fax +82-31-910-0211 E-mail: [email protected] b Senior Researcher, Korea Institute of Construction Technology, 2311 Daewha-dong Ilsan-gu Goyang-shi Gyeonggi-do, Korea E-mail: [email protected] This paper presents a study on an electrokinetic permeable reactive barrier which is electrokinetic remediation coupled with permeable reactive barrier system. In this study, electrokinetic permeable reactive barrier is filled with reactive materials such as atomizing slag & sand mixture, zeolite & sand mixture, and iron powder & sand mixture for remediation of soil and groundwater contaminated with heavy metal and organic substance. A series of laboratory experiments including variable conditions such as concentration of contaminants, magnitude of applied electrical current, operating duration, and reactive materials were performed with the contaminated soil and groundwater. Investigated are volume of water flow through soil specimen, the concentration changes of soil specimen, the current and voltage changes, and the concentration changes of groundwater inflow and outflow. The efficiency of heavy metal and organic substance removal by the proposed method was evaluated under various operating conditions. The test setup used in this study was made to combine the electrokinetic processor with permeable reactive barrier processor. The test chamber was made of a plexiglas box having an insider scale of 10cm x 10cm with a height of 10cm. The elecrokinetic with permeable reactive barrier processor consists of four parts: anode electrode, cathode electrode, electric power supplier, and permeable reactive material. Ethylene glycol and Cd were used as a surrogate contaminant to demonstrate the groundwater and soil contaminated by heavy metal and organic substance. The following left side figure shows the electrokinetic permeable reactive barrier test cell and the reactive material of black color is situated at right side reservoir of this cell. The following right side figure shows the volume of cumulative effluent passing through sediment specimen with different reactive material conditions.

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17

The tests were conducted for two conditions: electrokinetic remediation test (EK) and electrokinetic with permeable reactive barrier test (EK+PRB). In the tests, the clay soil specimens were thoroughly mixed with Ethylene glycol of 300ppm and Cd of 50ppm. The test specimen was then subjected to electric power at 2.0V/cm from electrokinetic test setup. Tests were continued to maximum 200 hr. The test result shows that the contaminant in soil and groundwater was effectively removed by composite reaction of electroosmosis, electromigration, washing efficiency, and reactive adsorption efficiency generated from electric power and reactive material. [1] Kyung Kook Lee, Ha Ik Chung, etc., “Remediation of contaminated soil by electrokinetic reactive washing ecopile”, Fall Conference of Korea Geotechnical Society, 2006.10

18


USE OF A PULSED ELECTRIC FIELD FOR RESISTING GROUNDWATER POLLUTION

J Reeve and R J Lynch Cambridge University Engineering Department, Trumpington Street, Cambridge CB2 1PZ, UK. E-mail: [email protected] When there is agricultural land close to mining areas there is often a need to prevent groundwater which contains heavy metal ions, from moving into unpolluted adjacent land. Previous work (Mitchell and Yeung, 1991, Narasimhan and Sri Ranjan, 2000, Lynch et al, 2007) has shown that an electric field can be used to keep out heavy metal pollutants from entering unpolluted soil. When such a barrier is to be used far from the national power supply it would be useful to employ solar power to provide the electric field. This work, investigates the use of pulsed power sources, similar to that produced by a photovoltaic panel.

A possible means of using the barrier is outlined in the schematic plan view in Fig.1.

Contaminant moving under hydraulic flow Contaminant redirected due to the electro-kinetic barrier

Cathode Anode

Region of agriculture that requires protection

Fig.1 A schematic representation of an electrokinetic barrier

A one dimensional electrokinetic cell test was used, as shown in Fig.2.

Power supply - +

Sampling points 1-4

19

Fig.2 Schematic diagram of a cylindrical electrokinetic cell test of the barrier The tube diameter is 11cm, and the length of the soil compartment is 22 cm. There is an electrode compartment on each side of the soil compartment which was filled with a fine sand of particle size range 90 - 150 microns. The copper-polluted water which is fed from a constant head device is driven through the cell in the absence of an electric field. An electric field of 1.7V/cm was applied when the copper reached sampling point (tap) 2. The effect of the field on the copper movement through the soil was monitored at the four sampling points distributed along the column, and also at the outlet.

Concentration of Copper at each port w ith time

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Power on

It is observed in Fig. 3 that hardly any copper reaches sampling points 3 or 4 when the power is applied, and that hardly any copper emerges from the outlet. The incoming copper concentration was 10 g/l, so about 99.95% copper has been excluded.

Further results of these experiments and a more complete analysis will be presented in the full paper.

Results obtained so far indicates that a pulsed electric field barrier should be possible.

References J K Mitchell and T C Yeung, Electrokinetic flow barriers in compacted clay, Transportation Research Record No.1228, Geotechnical Engineering 1-9, (1990)

Narasimhan and Sri Ranjan, Electrokinetic barrier to preventing subsurface contaminant migration: theoretical model and validation Journal of Contaminant Hydrology, 42, 1-17, (2000),

R.J. Lynch, A. Muntoni, R. Ruggeri and K.C. Winfield, Preliminary tests of an electrokinetic barrier to prevent heavy metal pollution of soils, Electrochimica Acta 52 (2007) 3432–3440.

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Metal Removal


PHOSPHATION OF BOTTOM-ASH FROM MSWI BY MEANS OF ELECTROKINETICS

G. Trainaa, S. Ferrob, A. De Battistib

aIstituto Giordano Spa, Via Rossini 2, 47814 Bellaria (RN), Italy; bDepartment of Chemistry, University of Ferrara, via L. Borsari 46, 44100 Ferrara, Italy E-mail: [email protected] Introduction

The incineration of MSW is one of the most increasing means of dealing with non recyclable solid waste. The benefits of MSW incineration are the reduction of solid waste volume and the opportunity to recover energy and use it for power generation in a waste-to-energy (WTE) facility. Of all waste incinerated, 20-30% by weight remains as bottom ash, while 3-5% as fly ash from flue gas cleaning devices. Bottom ash is by and large considered as non-hazardous waste but, in Italy, it’s required to pass a severe composition or leaching test (or both) to be acceptable for landfill or reuse. In Italy, separation of ferrous and non ferrous metals, as well as coarse and incombustible fractions, represent the common practice in view of ash recovery in cementary, but the more attractive recovery in road-base construction is limited by the leaching of some pollutants, such as Cu, Pb, Ba and chlorides, that often exceeds the limits established by Italian laws (according to the D.M. n° 186, 05/04/2006), and therefore expensive treatments of the ashes are required before bottom-ash re-use. The most common treatment, used to improve the environmental characteristics, is stabilization/solidification by means of organic or inorganic reagents. This can be applied for metal stabilization but in any case washing the ash to reduce leaching of chlorides is required. This “two-step process” could be expensive, and would also involve an important water management system. Therefore, this research aims at improving a new technique, hereafter referred to as an “electrochemical stabilization” for both metals stabilization and chlorides extraction, in the same reactor, by means of electrokinetics.

Results and Discussion One of the major drawbacks of using conventional (not enhanced) electrokinetic soil processing to remove heavy metal contaminants involves hydroxide precipitation in the soil fraction near the cathode [1]. The use of an enhancing agent at the cathode compartment, such as acetic acid, to prevent such defects has been largely tested. Previous works have shown good results in the electroremediation of bottom-ash [2], but even if the electromigration could be enhanced, long periods of treatment limit the real application of this technique. The electrochemical stabilization technique achieves the goal to shorten the time of treatment and to improve remediation of ashes by combining a faster extraction of chlorides, and partially of metals, by electromigration with a stabilization of metals by adding phosphate anions [3]; the latter originate from the electrolysis of H3PO4 at the cathode, and move through the ash by electromigration.

The paper presents two different cell configurations, with horizontal and vertical electrodes. In the first case, the anodes are placed on the bottom of the reactor with the cathode compartment on the top, while the second configuration follows the classical scheme of electroremediation. Anyway, the ash water is used as electrolyte at the anode interface whereas the cathode compartment comprises a pump for recirculating a phosphoric acid solution. This acid is used also as an enhancing agents at the cathode

23

(instead of acetic acid), while a micropore PET membrane is used to separate the ash from the cathode compartment to favour the movement of phosphate anions from the cathode towards the anode. The humidity of bottom ash has been increased up to 24% (w/w) for chlorides solubilization and the coarse ferrous and non-ferrous metals have been manually separated before the electrokinetic treatment. The test duration was varied between 24 and 48 h, applying 2-2.8 V/cm (DCV). The UNI EN 12457/2 method was followed to compare the leaching of pollutants from untreated and treated specimens, getting a considerable stabilizing effect for Ba and Pb by phosphatation, with a leachate reduction of 95-98%, while Cu leaching remained quite high and dependent on the solubility of Cu-organocomplexes. Phosphation did not show a significant effect in stabilizing these particular species, even if a measurable reduction of Cu-leaching (65 %) was found after the electrokinetic treatment. Chlorides extraction ranged between 50-85%, depending on the Amperage and the time of treatment.

References [1] Acar Y.B. & Alshawabkeh A.N. (1993) Environ. Sci. Technol., 46, 2638. [2] Traina G., Persano Adorno G., De Battisti A. (2005) “Electrokinetic Remediation: un nuovo approccio alla valorizzazione di cenere di fondo (bottom-ash) da incenerimento RSU”. Atti di Ecomondo, pp. 434 - 442 , Volume 2 Maggioli Editore. [3] Piantone P., Bodénan F., Derie R. & Depelsenaire G. (2003) “Monitoring the stabilization of municipal solid waste incineration fly ash by phosphation: mineralogical and balance approach”, Waste Management, 23, 225.

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ELECTRODIALYTIC REMOVAL OF TOXIC ELEMENTS FROM SEDIMENTS OF EUTROPHIC FRESH WATERS

Pernille E. Jensena, Lisbeth M. Ottosenb, Arne Villumsena

aARTEK, BYG•DTU, Technical University of Denmark, Denmark; bBuilding materials, BYG•DTU, Technical University of Denmark, Denmark. E-mail: [email protected] Introduction

The lack of adequate wastewater treatment technology in the past has resulted in deposition of a significant pool of phosphate in urban fresh water sediments. The eutrophication continues to shatter the water quality and the recreational life in affected areas due to a continuous phosphate release from the sediments. Dredging of the sediment is a rather simple process, which would permanently remove the phosphate source. Commonly, however, urban sediments contain high levels of toxic elemental contaminants arising from centuries of human activity along fresh water sources. Regulations require expensive deposition of such sediments in hazardous waste landfills, thus restoration has largely been restricted to less permanent solutions like biomanipulation and sediment coverage. Earlier works documented the feasibility of electrodialytic remediation (EDR) of fine grained waste products contaminated by heavy metals when suspended in an aqueous solution e.g.: removal of Cd, Cu, Pb and Zn from harbour sediments [1]; removal of Pb from soil fines [2]; and removal of cadmium from wastewater sludge [3]. The goal of this work was to investigate whether EDR of fresh water sediments contaminated by Cd, Cr, Cu, Ni, Pb, and Zn is feasible, and whether the resulting product is suitable for reuse e.g. as a valuable soil amendment material, rich in phosphate and organic matter, for poor agricultural soils.

Materials and methods

The experimental sediments were collected in the system of lakes and millponds called Mølleåsystemet north of Copenhagen, Denmark. Elements were analyzed by flame or graphite AAS. The carbonate content was determined by the Scheibler method. Organic matter was determined by loss of ignition. Phosphate was measured by spectrophotometer. pH and conductivity were measured by electrode. All measurements were made in triplicate. Electrodialysis experiments were made in cylindrical Plexiglas-cells with three compartments. Compartment II contained the soil-slurry, and was 10 cm long and 8 cm in inner diameter.

Fig. 1. Schematic view of a cell used for experimental EDR remediation of freshwater sediments. AN = anion-exchange membrane, CAT = cation-exchange membrane. I = anolyte compartment, II = compartment containing sediment slurry, III = catholyte compartment.

25

The slurry was kept in suspension by constant stirring with plastic-flaps attached to a glass-stick and connected to an overhead stirrer. The anolyte was separated from the soil specimen by an anion-exchange membrane, and the catholyte was separated from the soil specimen by a cation-exchange membrane. Figure 1 shows a schematic drawing of the setup. Platinum coated electrodes were used as working electrodes. The catholyte and the anolyte initially consisted of 0.01M NaNO3 adjusted to pH 2 with HNO3. pH in the electrolytes was kept between 1 and 2 by manual addition of HNO3 (7M) or NaOH (6M). The liquid to solid ratio (L/S) was 4 (100g soil and 400ml distilled water), and the current density was 0.8mA/cm2 (40mA). Four experiments of variable duration were made with each sediment.

Results and discussion Figure 2 illustrates the results of EDR of sediment from the Millpond “Raadvad-dammen” as a function of time. All elements could be reduced in concentration to values approximating background values. The current efficiency was high compared to remediation of harbour sediments [1], reducing the costs of the remediation. The high current efficiency probably relies on the lower concentration of soluble salts competing for the current in fresh water sediments. Unsatisfactory remediation could have been anticipated due to the immobilisation of heavy metals by high levels of phosphate and organic matter as described for Pb in previous works [4]. This effect was, however absent, and the release of metals caused by the shift in redox potential when the sediment was exposed to oxygen may be partly responsible for the successful remediation.

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Figure 2: Remediation results obtained with sediment from the Millpond “Raadvad-dammen” from the fresh water system Mølleåen north of Copenhagen.

[1] Nystroem G.M., Ottosen L.M., Villumsen A. (2005) Acidification of harbour sediment and removal of heavy metals induced by water splitting in electrodialytic remediation. Separation Science and Technology; 40, 2245-2264. [2] Jensen P.E., Ottosen L.M., and Ferreira C., (2007), Electrodialytic Remediation of Pb-Polluted Soil Fines (< 63my) in Suspension, Electrochimica Acta, 52, 3412-3419. [3] Jakobsen M.R., Fritt-Rasmussen J., Nielsen S., Ottosen L.M. (2004) Electrodialytic removal of cadmium from wastewater sludge. Journal of Hazardous Materials, 106, 127-132. [4] Jensen P.E., Ottosen L.M., Pedersen A.J. (2006) Speciation of Pb in industrially polluted soils. Water Air and Soil Pollution 170, 359-382.

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ENHANCED ELECTROKINETIC TREATMENT OF DIFFERENT MARINE SEDIMENTS CONTAMINATED BY HEAVY METALS

De Gioannis Giorgiaa, Muntoni Aldoa*, Polettini Alessandrab, Pomi Raffaellab

aUniversity of Cagliari, Department of Geoengineering and Environmental Technologies, Piazza d’Armi – 09123 Cagliari, Italy; bDepartment of Hydraulics, Transportation and Roads, University of Rome ‘‘La Sapienza’’, Via Eudossiana, 18-00184 Rome, Italy

e-mail: [email protected] It has been estimated that near 5% of watersheds in industrialised countries have health and environment threatening sediments and that 10% of marine and estuary sediments are potentially dangerous to aquatic environment. In fact, industrial activities are often located near the seashore, therefore it is not unusual that marine sediments are heavily contaminated, either by heavy metals or by organic contaminants. Sediment contamination is also problematic for marine trade routes. In fact, although contaminated sediments can be left in place covered by a low permeability and erosion-resistant capping and innovative in situ treatment technologies are under development, in many cases dredging is required, i.e. when maintenance or enlargement of harbours have to be performed. In these cases huge amounts of (probably) contaminated sediments have to be dredged, dewatered and treated before reuse or final disposal. Therefore, around 500 millions m3 of sediments are dredged each year for navigational purposes and roughly 1-4% requires dewatering and treatment prior to disposal, increasing the cost of dredging by a factor of 300-500. Presently, the most common approach to management of dredged sediment is generally limited to land (or aquatic) disposal and despite decades of research, surprisingly little is known about successful treatment of contaminated sediments. Sediment contamination is characterised by the possible simultaneous presence of several types of pollutants, inorganic and organic, which interact with different types of solid matrices. Therefore, a number of contaminants may affect a clayey or sandy matrix, more or less permeable, more or less rich in organic matter, containing particles with different surface properties, etc.; the high moisture and the salts content may also affect the treatment. While in soils the contaminated fine fraction is typically less than 50% of the total solid matrix, in sediments usually the opposite occurs, 80-95% are generally very finely grained particles. In these cases many treatment technologies have proved to be ineffective in order to achieve a reduction of the contaminant concentration. Sediment contamination is thus a complex technical framework which requires the study of different treatment alternatives and, likely, the synergic application of more than one. Electrokinetics is reported among the viable treatment alternatives for dredged marine sediments worth to be investigated; in fact, it could represent a possible solution in order to achieve dewatering and removal of heavy metals and salts in a single stage. In this framework electrokinetics was applied on two types of marine sediments sampled from the Veneto and South-West Sardinian coasts (Italy) in order to achieve at the same time dewatering and removal of heavy metals and salts. The sediments were previously characterised for the contaminant content and the main chemical-physical properties which influence the treatment; a contamination characterized by high contents of heavy metals (mainly Pb, Zn, Cu, As, Ni, Cd and Cr) was assessed for both the considered sediments [1], [2]. Lab-scale electrokinetic cells capable of maintaining a constant voltage up to 60V were used for a number of experimental runs. Tests were performed either on samples with or without a washing pre-treatment using soft water. Different operating conditions

27

(voltage, test duration) as well as cathodic and anodic solutions were adopted and tested in order to accomplish the main objective of mobilizing metals from sediments, favoring migration and avoiding precipitation. The enhanced electrokinetics made use of chelating agents (EDTA, citric acid), pH adjustment through the use of nitric acid solutions, and application of a hydraulic gradient. The evolution over time of circulating current intensity and density, of electrosmotic flow as well as the evaluation of pH and metal concentration in the electrode solutions was evaluated through periodical measurements over the treatment period. The efficiency of the process was evaluated on the basis of the achieved cathodic flow and of the residual concentration values of salt and contaminants in the solid sample measured at the end of the treatment. The results of the tests proved that EK is a suitable process in order to achieve either dewatering and removal of salts or the mobilization of the pollutants. The different characteristics of the sediments mirrored in the achieved heavy metal removal. In general, the enhancement of the process proved to be necessary in order to improve the overall efficiency of the process since prompt depolarization of cathode and higher heavy metals removal can be achieved. The results obtained indicated that in the case of real contaminated sediment, as compared to the results typically reported for spiked materials, the remediation efficiency is significantly affected by the buffer capacity of the sediment and by partitioning and speciation of metals in the less mobile fractions.

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Figure – Metal removal efficiency using different process fluids (W2: deionized water; CIT4: 0.2M citric acid; EDTA1: 0.2M EDTA)

[1] Ceremigna, D., Polettini, A., Pomi, R., Rolle, E., De Propris, L., Gabellini, M., Tornato,

A. Comparing sediment washing yields using traditional and innovative biodegradable chelating agents, Proc. 3rd International Conference on Remediation of Contaminated Sediments, New Orleans, Louisiana, USA, January 24-27, 2005.

[2] Ceremigna, D., Polettini, A., Pomi, R., Rolle, E., De Propris, L., Gabellini, M., Tornato, A. A kinetic study of chelant-assisted remediation of contaminated dredged sediment, submitted to J. Hazard. Mater., 2005.

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ELECTROREMEDIATION OF AN INDUSTRIAL AREA CONTAMINATED BY CHROMIUM

O. Merdoud1 and D. E. Akretche2 1Centre of Research in Physical and Chemical Analyses (CRAPC), BP39, El –Alia, 16111 Bab-Ezzouar, Algiers, Algeria 2Laboratory of hydrometallurgy and Inorganic molecular chemistry, Department of chemistry and physics of inorganic materials, Faculty of Chemistry, U.S.T.H.B BP32, El - Alia, 16111 Bab-Ezzouar, Algiers, Algeria Fax : 213-21247298, email : [email protected] ABSTRACT

A great area located near a refrigerators manufactory contains a high amount of sludge which contains essentially chromium hydroxides. The industrial area concerned is sited at Tizi Ouzou (100 km at the east of Algiers) and it induces a great contamination of neighbor’s soils by chromium knowing that sludge can be dissolved under varying pH and meteorological conditions. The analyses of some samples have shown the presence of both Cr(III) and Cr(VI) with an amount which approaches 5mg/g in some parts. Electroremediation has been tested for the treatment of these samples using a cylindrical laboratory cell. It consists in a five compartment where the two extremities there are two metallic electrodes (platinum - coated titanium sheets). A weighed amount (90.0 ± 2.0g) of the soil is put in the central compartment and saturated with deionized water. The adjacent compartments are composed by various acids and they are separated by alternated ion exchange membranes. The applied voltage is delivered by a power supply (Consort E802) and maintained constant in all the runs at a value of 15.5 V corresponding to electric field strength of 1 V.cm-1. Chromium concentration in both anolyte and catholyte is followed as a function of time by means of atomic spectrophotometer Perkin Elmer 2380 and by spectrophotometric measurements using an UV-Visible Spectrophotometer JASCO V530.

After speciation and experiments with a duration which vary between 20 days and 42 days, we have reached a removing yield of 78%. The influence of the nature of the acid has been studied and it shows that nitric acid can oxidize chromium and remove it only through the anion exchange membrane toward the anode. Other acids (HCl and H2SO4) give rise to ion transfer toward the two electrodes showing that the chromium is present at two oxidation state. The influence of the pH and the current behavior have also been examined in this work.

Results have shown a contribution in the understanding of the removing mechanisms in the course of the electroremediation of a soil contaminated by chromium.

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BENCH SCALE EVALUATION OF HEXAVALENT CHROMIUM REDUCTION AND CONTAINMENT USING FIRS (FERRIC IRON

REMEDIATION AND STABILISATION) TECHNOLOGY

Anne Hansena, Laurence Hopkinsonb, Andrew Cundyb, Ross Pollocka

aChurngold Remediation Limited, St Andrews House, St Andrews Road, Avonmouth, Bristol,BS11 9DQ, UK; bSchool of the Environment, Civil Engineering Division, University of Brighton, Moulscoomb, Brighton, BN2 4GJ, UK E-mail: [email protected] Introduction The aim of this study was to investigate if FIRS, a novel electrokinetic technique, can be used to reduce the carcinogenic and mobile Cr(VI) to the less toxic and less mobile Cr(III), and lock up the Cr(III) in iron. FIRS is a, low energy contaminant reduction/containment technique that has the potential to be used to remediate heavy metal contaminated soils and sediments. The FIRS technique involves the application of a low magnitude direct electric potential between opposite polarity iron electrodes emplaced in or either side of a contaminated soil or sediment. The electric potential is used to generate a strong pH (and Eh) gradient within the soil column, promote dissolution of the anodic electrode(s) and force the precipitation of an iron rich barrier in the soil at the point of the pH jump. The iron-band generated by the technique contains iron in its elemental Fe, Fe(II) and Fe(III) valence states[1], held within a variety of iron mineral phases, which constitute the precipitated iron stone barrier.

Chromium usually exists in two different valences in the near surface environment; Cr(III) and Cr(VI), depending on the redox state of the local environment. Cr(III) exists as cations, while Cr(VI) usually existed as toxic oxyanions. Cr(VI) species are soluble over a wide pH range and will migrate towards the anode during electrokinetic treatment [2]. It has been estblished that reduction of Cr(VI)in the presence of Fe(II)occurs instantaneously as shown by the following reaction:

Cr2O72- +14H + +6 Fe2+ 2Cr 3+ + 6 Fe3+ + 7H2O

When Cr(VI) enters the acid anode zone, developed by the FIRS technology, it comes into contact with Fe(II), which is migrating in solution, away from the dissolving anodic electrode(s) and is reduced to less mobile Cr(III) which accumulates near the anode electrode, Fe(II) and Feo is simultaneously oxidised, and stable inert Cr(III) – bearing ferric iron mineral phases are produced. Presented below are the results of a laboratory experiment on the remediation properties of FIRS, with respect to Cr(VI) contaminated soils. Chemical analyses were conducted at a certified laboratory.

Results

50kg soil was treated in a 700mmx300mmx300mm test cell. The initial concentration of total Cr and Cr(VI) in the soil was 9300mg/kg soil 740mg/kg respectively. After running the experiment for 5 weeks at 75V the concentration of Cr(VI) was 240 mg/kg and 35 mg/kg near the anode and cathode respectively. Concentration of total Cr was 24000 mg/kg and 6300mg/kg near the anode and cathode respectively. The results are presented in figures 1 and 2. These figures show the initial concentrations and the concentrations across the experimental cell after 5 weeks.

31

Figure1. Total Cr concentration in kg soil Figure 2. Cr(VI) concentration in kg soil

Total Cr concentration in kg soil

0

5000

10000

15000

20000

25000

5cm 15 cm 25 cm 35 cm 45 cm

Distance from anode

mg/

kg

Initial conc. Total Cr

Total Cr(VI) concentration in kg soil

800

0

200

400

600

5cm 15 cm 25 cm 35 cm 45 cm

Distance from anode

mg/

kg

Initial conc. Total Cr(VI)

The experiment was terminated before an iron band had formed. Scanning electron microscopy (SEM) reveals the presence of abundant chromium bearing iron minerals within the treated soil (Figure 3). In summary the experiment results show that FIRS treatment, over comparatively short experimental time frames has resulted in a 96% reduction in the concentration of Cr(VI) within the soil, and an 27% build up of precipitated iron within the anodic compartment, association with an 100% build up of chromium within the same zone. Moreover, SEM images suggest that the precipitated chromium is locked up in poorly crystalline fine grained iron-rich minerals.

Figure 3 SEM photo and graph

Conclusions While the efficiency of all electrokinetic techniques are in measure a function of soil-specific properties, e.g., buffering capacity, etc, the experimental results are highly promising in that they clearly show that FIRS shows considerable potential to remediate Cr(VI) contaminated soil and groundwater. An in-situ pilot scale test is being developed to follow up these results [1] A.B Cundy and L. Hopkinson, Applied Geochemistry.20 (2005) 841-848. [2] K.R. Reddy and S. Chinthamreddy, Advances in Environmental Research. 7 (2003) 353–365 [3] K.R. Reddy, U.S. Parupudi, S.N. Devulapalli, C.Y. Xu, J. Hazard. Mater.55 (1997) 135–158

32

Oral Contributions to session 3 New Applications – Inorganic Pollutants


DELIVERY AND ACTIVATION OF NANO-IRON BY DC ELECTRIC FIELD

Sibel Pamukcua, Laura Hannumb, J.Kenneth Wittlec aDepartment of Civil and Environmental Engineering, Lehigh University, Bethlehem, Pa 18015, USA; bDepartment of Civil and Environmental Engineering, Virginia Tech, Blackburg, VA, USA; cEPI, Wayne, PA, USA E-mail: [email protected]

Previous studies have demonstrated that nano-iron can be highly effective to transform recalcitrant organic compounds, such as chlorinated hydrocarbons (CHCs), trichloroethylene (TCE), and heavy metals to less toxic or non-toxic oxidation states. Nano-iron can be introduced to soil hydraulically in slurry form. However in low permeability clay sediments, delivery of a uniform distribution of the slurry may be difficult to achieve effective remediation. In most soil types, the contaminants are retained in clay interstices, or present in the form of immobile precipitates and products in pore throats and pore pockets that “lace” the entire porous matrix. This exacerbates the situation as the available technologies may not treat a site effectively. Additionally, when hydraulic delivery is considered, the limited life of the nano-iron particles, necessitates the need for adequate amount of nano-iron particles to reach the contaminant targets in time before the iron becomes ineffective by oxidation or precipitation. Electrokinetics is a proven, sustainable technology that can transport liquids and slurries in clay rich medium at a significantly higher rate than hydraulic methods. Furthermore, in previous investigations [1], the application of direct electric current in clays was observed to contribute to the success of the desired transformation reactions by not only providing the advective force for the delivery of active reagents, but also by lowering the energy for the redox reactions to occur. This increase was attributed to the possible over-potential created by double-layer polarization of the clay surfaces leading to Faradaic processes under the applied electric field.

This study demonstrates that by integrating electrokinetics with nanotechnology, the transport of nano-particles can be electrokinetically enhanced for subsurface remediation of tight clay soils where transport time and process efficiency may be an issue. The injection of nano-iron particles in both the field and lab tests showed a drop in the redox potential [2], where the effectiveness of nano-iron as an environmental catalyst was demonstrated. The nano-iron particles are zero-valent (Fe0) and have a diameter less than 100 nm for 80% of slurry batch sample. Polymer coated dispersed nano-iron, developed at Lehigh University, was used as the iron input into the system. Due to the polymer coating, the iron particles tend to repel each other, and as a result, remain suspended in solution rather than settling over time as occurs with bare nano-iron. The iso-electric point (IEP) of the nano-iron, which is the critical value at which the net surface charge is zero, occurs at a pH of 8.3 and was found to be independent of iron concentration [2]. Using saturated Georgia kaolinite clay and 2.0M NaCl solution was used to make a soil paste with 60% water content. A 2 mm thick uniform layer of the paste was spread onto a modified electrophoretic (EP) cell tray equipped with transversely running platinum wires. A constant potential of 5.0 V was applied across the electrodes, as the nano iron was introduced into the clay by simply pouring a slurrified form of it into a pre-opened grove on the anode side of the sample.

35

It was determined that the redox potential reduced across the soil bed from anode to cathode, indicative of nano-iron transport from anode to cathode, as shown in Figure 1. The presence of nano-iron pushed the redox potential to higher positive values at low pH (anode side), while lowering it to higher negative values at high pH (cathode side) than the electrokinetic effects alone. The diffusion of nano-iron without the electrical field showed no activation of the iron, as indicated by little or no change in the redox potential for the diffusion sample in Figure 1. These results showed that nano-iron was both transported and activated by the applied electrical field.

Figure 1: Redox Potential vs. Distance - Test Comparison

The electrokinetically enhanced transport and activation of nano-iron were evidenced by the higher negative potentials achieved in nano-iron specimens on the cathode side, at the same pH for the same test durations of the control specimens. Figure 2 shows the variation of redox potential (Eh) versus pH. The variation of Eh vs. pH in the electrokinetics only specimen follows closely the lower bound for electrolysis of water, while when nano-iron is transported using electrokinetics the system displays higher oxidation potential for iron.

(a) (b)

Figure 4: Soil Bed at 46.0 hrs

(a) Diffusion Only (b) Electrokinetically Enhanced ______________________________________________________________________ [1] Pamukcu, S., Weeks, A., and Wittle, Kenneth J. (2004). “Enhanced Reduction of Cr

(VI) by Direct Electric Field in a Contaminated Clay.” Environ. Sci. Technol., 38, 1236-1241.

[2] Sun, Y.P., Li, X.Q., Cao, J., Zhang, W.X , and Wang, H.P. (2006). “Characterization of Zero-valent Iron Nanoparticles.” Advances in Colloid and Interface Science, 120:47-56.

36


ELECTRO-RECLAMATION OF CYANIDE, IMPOSSIBILITY OR OPPORTUNITY?

Bas Godschalk, Wiebe Pool Holland Milieutechniek BV P.O. Box 48, 4190 CA Geldermalsen, the Netherlands Tel. +31 345 473 733 Fax +31 345 473 730 [email protected] In the middle of many cities company grounds are situated of former gas plants. The gas plants have been used for decades in the previous century. Today, the gas plants are closed or used as storage or parking place. Many municipalities are planning to redevelop these areas for living or shopping areas. However, the soil is heavily contaminated with PAH, mineral oil, acids and very common cyanide. The gas factories have produced city gas by transforming coal into gas. During this process, the gas had to be cleaned before use. One of the pollutants is hydrocyanic. It has been removed by dry washing of the gas with ferruginous earth (bog ore). Hydrocyanic will react with iron and form iron cyanide complexes. The ferruginous earth has been regenerated many times. When the activity of ferruginous earth has been reduced, the earth will be sold or used as raising material around the factory. The ferruginous earth contains after use about 10 % iron cyanide complexes. The iron cyanide complexes will dissolve during by the weather conditions and start to spread over the site through water canals and through pores of the soil. Today, the cyanide will be mainly present as iron cyanide complexes (such as Berlins Blue), thiocyanate and the very soluble ionic cyanide. Especially free cyanide could spread very easily through the soil. Due to the great interest in redeveloping these plants, effective and economic solutions are required. One common method is excavation of the whole plant. Especially, PAH and tar should be treated by excavation. However, cyanide soluble in groundwater could be present in a big volume and at great depths. Therefore, a in situ method will be desirable. Holland Milieutechniek has developed and successfully applied the in situ Electro-Reclamation method for the cyanide contaminants. Electro-Reclamation is developed as an in situ method for removing contaminants like heavy metals, cyanides and other electrical charged components from low permeable soil types. Electrodes are installed in the contaminated soil and by creating a DC current electrical charged particles like ions and ion complexes will move to and captured at the special designed electrodes. Electro-Reclamation can easily take out the ionic cyanide and thiocyanate. But low soluble iron cyanide complexes, such as Berlins Blue have to be transformed in ionic form before they can be transported to the electrodes. Laboratory and field research, has shown that the Berlins Blue complex could easily dissolve at a pH of 7 or higher. Therefore, the pH of the soil has to be increased. Electro Reclamation can also be used

37

as an in situ method to change the soil pH. In this way the soil pH could be increased and the Berlins blue will dissolve in iron and ionic cyanide complexes which will be transported by the electro kinetic processes. Holland Milieutechniek has tested the technology in the laboratory and proven the proper working of this method. Efficiency up to 99% is common in all types of soil. Therefore, the method has been demonstrate in a pilot, which was successful. Electro-Reclamation has shown to overcome the impossibilities of iron cyanide complexes and will have great opportunities to be the in situ method of cyanide contaminations.

38


ELECTROKINETICALLY ENHANCED REMOVAL AND DEGRADATION OF NITRATE IN THE SUBSURFACE USING

NANOSIZED Pd/Fe SLURRY Gordon C . C. Yanga, Chih-Hsiung Hunga, Hsiu-Chuan Tua

aInstitute of Environmental Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan. E-mail: [email protected] 1. Introduction In recent years injection of nanoiron (nanoscale zero-valent iron) slurry to the groundwater for remediation of various contaminants (e.g., trichloroehylene, nitrate, and pesticides) has been demonstrated in more than 20 sites worldwide [1]. However, only limited studies had forcused on the transport of nanoiron in the subsurface environment [2, 3]. Yang [2] employed a slurry of nanoiron modified by an anioinc surfactant to evaluate its ability to transport through vertical and horizontal soil columns. It was found that the specific nanoiron slurry could easily travel through a 15-cm vertical silica sand column without difficulty. However, it took more than 25 hr to travel through the same vertical column filled with a real loamy sand soil. Based on the experimental data and deep-bed filtration theory, a sticking coefficient was calculated. Further, a transport distance of 0.25 m was estimated for such nanoiron slurry to travel under typical groundwater conditions. An additional study conducted in a horizontal loamy sand column saturated with a simulated groundwater by applying an electric field gradient of 1 V/cm revealed that the transport distance of the nanoiron slurry was 10-fold greater. After analyzing the mass balance of iron, it was postulated that a certain amount of nanoiron had been transported in the groundwater saturated loamy sand by the electroosmotic flow. In a separate laboratory-scale study [4] using a hybrid technology of injecting surface-modified nanoscale Pd/Fe slurry into the anode reservoir of an electrokinetic (EK) remediation system, it was found that 92.44% of trichloroethylene (TCE) in the loamy sand soil body has been degraded as compared with the blank test of 2.09% reduction in TCE due to evaporation during the 6-day test period.

This work was aimed to further evaluate the effectiveness of in situ removal and degradation of nitrate in the subsurface using the slurry of Pd/Fe bimetallic nanoparticles under an electric field. 2. Experimental All chemicals used in this work are reagent grade unless otherwise specified. The same surface-modified nanoscale Pd/Fe slurry as used elsewhere [4] was selected and tested in this work. Fig. 1 shows the schematic diagram of the EK system used in this work. In which, the soil compartment was packed with a simulated nitrate-contaminated loamy sand (850 g soil + 150 mL of nitrate solution having a concentration of 150 mg/L) that was saturated with a simulated groundwater. Except Test 1 (i.e., applying only electric field without any addition of dispersant), in all other tests (see Fig. 1) a daily addition of 20 mL of surface-modified nanoscale Pd/Fe slurry (@ 4 g/L) was practiced. More specifically, 10 mL/day of the aformentioned slurry was added to each injection port for Tests 4 and 5. In all tests, a constant electric field gradient of 1 V/cm and treatment time of 6 days were employed.

39

A V

(+)

G raphite E lectrode

A node R eservoir C athode R eservoir

Pow er Supply

Test 2 Test 3Test 4 Test 5

(-)

Fig. 1. The schematic diagram showing the electrokinetic remediation system and slurry injection locations for various tests

3. Results and Discussion In the case of applying EK alone (i.e., Test 1), about 90% of nitrate was removed from the soil compartment to the anode reservoir. The EK results for Tests 2-5 are shown in Fig. 2. Test 4 was found to yield the best result of nitrate removal and degradation.

A node R eservoir A -05 A -10 A -15 A -20 C athode R eservoir0

500

1000

1500

2000

2500

3000

Tota

l Mas

s of R

esid

ual N

itrat

e (m

g)

Position

Test 5 Test 4 Test 3 Test 2

Fig. 2. Residual nitrate in different locations of the electrode reservoirs and soil compartment for Tests 2-5.

4. Conclusions By injecting 0.05 wt% of surface-modified nanoscale Pd/Fe slurry into the anode reservoir of the EK system an over 99.2% efficiency of nitrate removal and degradation for the entire system was achieved. The cathode reservoir is the worst injection spot.

[1] Li, X.Q.; Elliott, D.W.; Zhang, W.X. Zero-valent iron nanoparticles for abatement of environmental pollutants: materials and engineering aspects, Crit. Rev. Solid State Mat. Sci. 2006, 31, 111-122.

[2] Yang, G.C.C. In Stability of Nanoiron Slurries and Their Transport in the Subsurface Environment, Proceedings of International Symposium on Environmental Implications and Applications of Nano-sized Materials, Taichung, Taiwan, Dec. 14-15, 2006.

[3] Saleh, N.; Sirk, K.; Liu, Y.; Phenrat, T.; Dufour, B.; Matyjaszewski, K.; Tilton, R.; Lowry, G.V. Surface modifications enhance nanoiron transport and DNAPL targeting in saturated porous media, Environ. Eng. Sci. 2007, 24, 45-57.

[4] Yang, G.C.C.; Chang, D.G. Degradation of trichloroethylene in the subsurface by nanoscale bimetallic Pd/Fe slurry under an electric field. In EnviroNano 2006, Yang, G.C.C. Ed.; Kaohsiung, Taiwan, 2006; 40-47.

40


SPENT CAUSTIC OXIDATION USING ELECTROGENERATED FENTON’S REAGENT IN A BATCH REACTOR

Henrik Hansen, Patricio Nuñez, Nicolas Rodriguez. Universidad Técnica Federico Santa María, Av. España 1680, Valparaiso, Chile E-mail: [email protected] Introduction Spent caustic is the product of the extraction of Sulphurs and Marcaptans in Petroleum Refineries. Spent Caustic is considered to be a hazardous Waste, and its treatment and final disposal must be adequate to that nature [1,2]. The main hazardous characteristics of this waste are the high COD (Chemical Oxygen Demand) and the high amount of sulfide. Normally the WAO (Wet Air Oxidation) technology, which uses oxygen to oxidize the Spent Caustic at high temperatures (between 200 and 280[°C]) and high pressures (up to 150[bar]), is used [3]. This treatment is expensive and only useful as a pretreatment process. Furthermore, because of the reaction and the pressure it carries several safety problems. An alternative treatment, a pH reduction followed by an Electro-Fenton process, is recommended for this waste [4,5]. Experimental The Electro-Fenton process is a partial production of Fenton’s reagent in a 2.5 [L] cubic-glass-made reactor, where the Waste stream flows through a labyrinth made by ferrous plates, which are connected to a direct current source (see Figures 1 and 2). The experiments were conducted with a synthetically made wastewater. This was prepared with Phenol (2,500 ppm) and Sodium Sulphydrate (10,000 ppm of Sulfides), with an initial pH of 9.28. The Fenton’s reagent was completed with a Hydrogen Peroxide stream that was supplied in a stoichimetric proportion. The agitation in this Batch reactor was made by two serial 8 [lpm] pumps, which forced the liquid Waste, and the Fenton’s reagent, to flow across the internal labyrinth. The Liquid Waste and Hydrogen Peroxide are perfectly mixed through the labyrinth. The reactor was built considering a large difference between the length of the ferrous plates and the distance between them. To modelate the reactor the axial dispersion produced in the inlet was considered using Péclet’s number, considering the Reactor as a Plug Flow.

Figure N°1. Upper view of Electro-Fenton’s reactor Figure N°2. Vertical view of Electro-Fenton’s reactor

41

Background The Fenton’s main reactions are showed in the following equations proposed by Cheves Walling [4]:

*2

*

*2

*

32*

*3222

3

3

2

1

)3(

)3(

)2(

)1(

RjOHHRHOj

RiOHHRHOi

HOFeFeHO

HOHOFeFeOH

j

i

k

j

k

i

k

k

+→+

+→+

+→+

++→+

−++

−++

Fenton’s reagent is a strong oxidizing agent, because of the OH radicals produced in (1). Its oxidizing rate is 2.06 times Chlorine (Cl2) relative oxidation power. The oxidation occurred mostly close to the layers of the electrolytes. Considering Grahame’s Double Layer schema it occurred in the Internal Region, between the Internal and External Helmholtz Even Layer. Because of the less amount of catalyst, Fe+2, the oxidation in the External Region had a slower oxidation rate. The Electro-Fenton reactor was proved varying a) the Ferrous ion concentration ([Fe+2]), b) the Spent Caustic’s initial Temperature and c) the initial pH. Results Removal of close to 95% of the COD was achieved with a pH of 4, a temperature of 30°C and 100 [mg/L] of Fe+2(1[A]). The treatment time was between 10 to 60 minutes, showing that 40 minutes was suffiencient for efficient treatment. Phenol content was equally reduced with 95 %. Conclusions The removal of COD showed that Electro-Fenton’s reactor is a very useful process for this waste treatment. Its safety and costs advantages make it a process that has to be considered in Petroleum Refineries.

[1] Cordonnier, F.B.a.J., Refining, Petrochemicals and Gas Processing Techniques.

INDUSTRIAL WATER TREATMENT. 1 ed. Vol. 1. 1995, Houston, Texas, USA: Gulf Publishing Company. 248.

[2] ENAP Refinerias Aconcagua, I.d.P., Produccion de Sodas Gastadas. 2005: Con Con.

[3] Nikolai Markovich Emanuel, E.T.D., Zinada Kushelevna Maizus, Liquid-Phase Oxidation of Hydrocarbons. 1st ed. 1967, Moscow, USSR: Plenum Press.

[4] Walling, C., Fenton's Reagent Revisited. Acc. Chem. Res., 1974. 8: p. 125. [5] Weng, S.-H.S.a.H.-S., Treatment of Olefin Plant Spent Caustic by Combination

of Neutralization and Fenton Reaction. Water Research, Elsevier Science Ltd., 2000. 35: p. 2017-2021.

42


PHYSICOCHEMICAL STUDY OF CLAY SOIL USING INERT AND STEEL ELECTRODES

C. Liaki*, C.D.F. Rogers and D.I. Boardman Department of Civil Engineering, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom. Email: [email protected] This abstract presents a recently completed research study (Liaki, 2006), which was conducted at the University of Birmingham, UK. Mechanisms, and resulting effects, of the application of an electric gradient across English China Clay (ECC, a relatively pure form of kaolinite) samples using either ‘inert’ electrodes or steel electrodes were investigated. The study’s aim was to explore the science, and thereby 'prove the concept' and establish the practical possibilities, of providing an adequate empirical foundation from which to bring about, via the introduction of hydrated chemical stabilisers, the classical chemical modification and stabilisation reactions in situ using an electrokinetic technique. Current attempts to create such a basis are mired in the uncertainties associated with clay types, clay chemistry and electrode reactions. Homogeneous ECC samples were electrokinetically treated for 3, 7, 14 and 28 days using the experimental set-up presented in Figure 1. They were then tested for Atterberg limits, undrained shear strength, water content, pH, conductivity, Fe concentration and zeta potential. Water flowed through the system from anode to cathode affecting the undrained shear strength, as expected. Acid and alkali fronts were created around the anode and cathode, respectively, affecting the pH, conductivity and zeta potential of the soil. Variations in zeta potential were associated with flocculation and dispersion of the soil particles, thus raising or depressing the Atterberg limits and the undrained shear strength. When the pH was raised (>7.0) mineral dissolution, and hence creation of metal silicate hydrates and/or metal aluminate hydrate gels, which subsequently crystallised, was postulated. Redox reactions occurring at the metal electrodes increased the Fe concentration in the soil, which also affected the zeta potential and the conductivity. Formation of precipitates contributed to decreases in the LL and PL. A novel means of indicating strength improvement by chemical means, i.e. free from water content effects, is presented to assist in interpretation of the results (Figure 2). Any points lying above the curve demonstrate physicochemical improvement, while any points lying below the curve demonstrate physicochemical detriment. The data obtained showed different performance between the two types of electrodes used. The ‘inert’ electrodes provided lower pH values, thus creating a more acidic environment. Thus when electrokinetic remediation of soil is being considered, ‘inert’ electrodes perform better than ordinary steel electrodes. They were also proved to be more durable than the steel electrodes, although less energy efficient. The improvement in the physical properties of the soil was more significant when steel electrodes were used. No significant differences between the two electrode types were observed in the physical properties near the cathode. Reference LIAKI C. Physicochemical Study of Electrokinetically Treated Clay Using Carbon and Steel Electrodes. PhD Thesis, University of Birmingham, UK, 2006.

43

Clay Specimen

Water Chambers

Water Feeding Bottle

AnodeCathode

Power Supply

Industrial Filters

Collecting Beaker

FIGURE 1. Electrokinetic Treatment Arrangement with the Consolidated Clay Specimen Formed and the Solid Tank Base in Position.

0

2

4

6

8

10

12

14

45 50 55 60 65 70

Water Content (%)

Und

rain

ed S

hear

Str

engt

h (k

Pa)

Control

FIGURE 2. Relationship between Soil Undrained Shear Strength and Water Content (NB The control data are for untreated clay consolidated from a slurry to different water contents)

44


MICROSTRUCTURAL CHANGES IN A CEMENTITIOUS MEMBRANE DUE TO THE APPLICATION

OF AN ELECTRICAL FIELD A. Covelo, B. Díaz, L. Freire, X. R. Nóvoa, M. C. Pérez Universidade de Vigo, E.T.S.E.I. Rúa Maxwell 9, Campus Universitario Lagoas-Marcosende, 36310 Vigo, Spain. E-mail: [email protected] Electromigration refers to the movement of ions caused by the existence of an electrical field in an ionically conducting. Applications of these techniques are numerous including not only soil remediation but also any kind of topic which is conditioned by ionic motion, i. e., cathaphoretic painting, chloride extraction, electroosmotic filtering, etc.

In relation with concrete, electromigration techniques have been used since 80’s to accelerate chloride movement in order to obtain diffusion coefficients in a shorter period of time. These techniques have experienced numerous modifications during this time concerning mainly experimental setup conditions: applied voltage, employed solutions or testing time. However, studies about microstructural changes caused by the electrical voltage are rather limited. The interest to know diffusion coefficients is twofold: it is determinant on predicting structures service life, but also it is related to remediation measures as chloride extraction.

Here the effect of the electrical field on a cement porous membrane will be analysed. In this research a study about microstructural changes during the electromigration test is detailed. Although only concrete membrane will be discussed, similar changes are expected to take place in other types of inorganic membrane - like systems as soils.

Electrochemical Impedance Spectroscopy (EIS) was introduced during 90’s as a useful technique to characterize the microstruture of concrete. Basically, it consists on applying an AC potential to an electrochemical cell, measuring the resulting current through the cell. The ratio between both parameters will be the impedance of the system. Some previous works [1,2] have established the high frequency domain (> 1 kHz) as suitable to find adequate information. Besides, Mercury Intrusion Porosimetry (MIP) was employed to characterise the pore structure. It is a technique widely spread and parameters as total porosity or average diameter size can be obtained. Results from both techniques will be complementary and allow to obtain useful information on the evolution of the microstructure of the material [3].

A comparison between natural diffusion (without external voltage applied) and migration experiments on samples with the same characteristics has been carried out. The results present differences regarding to the final resistance obtained after that experiments, as figure 1 shows. When an electrical field is applied, the global impedance undergoes an important increase in a shorter period of time compared to natural diffusion tests. So, the forced motion of ions through the concrete membrane induces significant variations in the porous structure. However, to obtain useful information from these tests, spectra must be fitted to an equivalent electric circuit (fig. 1, left). Each one of these components is associated to a physical parameter in the porous membrane. A detailed analysis of the variation of those parameters with test time will explain the microstructural changes observed. More details of this analysis will be presented in the final paper.

45

0.0 0.1 0.2 0.3 0.4 0.50.0

0.1

0.2

0.3

0.4

0.5

C1

C2

R1

R2

28 days 24 weeks

- Im

agin

ary

part

Real Part / k Ω. cm2

40 MHz

100 Hz

0.0 0.1 0.2 0.3 0.4 0.5

0.0

0.1

0.2

0.3

0.4

0.5

2 days 28 days

- Im

agin

ary

part

Real part / kΩ cm-2

40 MHz

100 Hz

Figure 1. Nyquist spectra from natural diffusion (left) and migration experiments (right) through a mortar sample.

Finally, MIP results corroborate EIS measurements. After migration experiments an important increase on the capillary pore size (10-100 nm) is detected. However, after natural diffusion tests no relevant variations are found.

1 M. Keddam, H. Takenouti, X. R. Nóvoa, C. Andrade, C. Alonso, Cem. Concr. Res. 27, 1191 (1997). 2 C. Andrade, V. M. Blanco, A. Collazo, M. Keddam, X. R. Nóvoa, H. Takenouti, Electrochim. Acta 44, 4313 (1999). 3 M. Cabeza, M. Keddam, X. R. Nóvoa, I. Sánchez, H. Takenouti, Electrochim. Acta 51, 1831 (2006).

46


EFFECT OF THE ELECTROLYSIS TIME IN THE MOVEMENT OF NITRATES IN AN ANDISOL OF ANTIOQUIA (COLOMBIA)

Diego A. Vascoa, Felipe Hernández-Luisb, Carmen D. Arbeloc, Mario V. Vázqueza* a Instituto de Química, Univ. de Antioquia, A.A. 1226, Medellín, Colombia b Departamento de Química Física, Univ. de La Laguna, 38206 Tenerife, España c Departamento de Edafología y Geología, Univ. de La Laguna, 38206 Tenerife, España Introduction The electrorremediation has been used in the last years as method of decontamination of soils, taking advantage that the application of an electrical field gives origin to a series of phenomena of transport that propitiate the pollutants' removal [1] And also has proved to be a useful in order to obtain parameters of agricultural interest [2]. The use of fertilizers in excess can provoke alterations in the environment that they can affect even the human health. These fertilizers can drive, for example, to an important increase in the concentration of nitrates in the solution of soil. Given the high solubility of this ion and his low retention for the soils can accumulate in the residual waters, being the agricultural practices the principal pollution source in this respect. Due to their charge it is possible to study his movement by means of the use of electrical fields. These kind of studies of electro-migration have been reported in different types of soils [3, 4] In the present work results obtained in the study of mobility of ions nitrate in samples of Andisol from the Department of Antioquia, a zone where takes place an important activity of culture of flowers, are presented. Experimental The samples of soils were prepared following the procedure developed in the laboratory [1,2]. It consists basically of the preparation of a humid paste that is left to balance 24 hours before beginning the electrokinetic study. This paste is incorporated later into the electrorremediation cells where an electrical field of 1,20V.cm-1 is applied. This study was realized to different conditions, treatment time, nitrate concentrations, etc. After the electrochemical treatment, the samples were fragmented to be able to evaluate the residual composition of nitrate to different distances of the electrodes. This quantification is obtained by means of the employment of a solution extractante the posterior evaluation using a selective electrode to ions nitrate. On the other hand pH, conductivity and electrolysis current variation was evaluated. These electrodynamics studies, they were compared with analysis of movement of nitrate in columns of the soil under study. All the experiments were performed by duplicate. Discussion The following figures show the pH variation inside the soil after the electrochemical experiment as well as the electrolysis current variation during the treatment. For comparison the results obtained with a soil without nitrate ion added is presented.

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relative position to cathode1 2 3 4 5

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4,00

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Chamber [NO3-], M

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Nitrate concentration at the electrode chambers after the electrochemical treatment In spite of the major content of ions when nitrate ion is present, the regulatory capacity of the soil keeps the pH invariable, though there is an important increase of the current of electrolysis. The analysis of the residual nitrate concentration in the electrode chamber after the treatment allows verify the effect of the electrical field applied to mobilize the pollutant. References [1] Vázquez MV, Hernández-Luis F, Lemus M, Arbelo CD. Integral Analysis of the

Process of Electro-Remediation of Andisols Polluted by Heavy Metals. Portugaliae Electrochimica Acta 2004; 22: 387-398.

[2] M.V.Vazquez, F.Hernández-Luis, D. Benjumea, D.Grandoso, M.Lemus, C.D.Arbelo; Science of the Total Environment (2007) in press [3] N. Eid, W.Elshorbagy, D.Larson, D.Slack; Journal of Hazardous Materials, B79(2000)133-149. [4] T.B.S. Rajput, N. Patel; Agricultural Water Management 79(2006)293-311

48


COMPARATIVE COST ANALYSIS OF THE ELECTRO-FENTON AND THE PHOTOELECTRO-FENTON PROCESSES

Ahmet Altina, Eyüp Atmacab, Süreyya Altina

, Vural Evrena

aDept. of Environmental Eng. Z. Karaelmas University, 67100-Zonguldak-TURKEY; bDept. of Environmental Eng. Cumhuriyet University, 58140-Sivas-TURKEY E-mail: [email protected] ABSTRACT Electro-Fenton (EF) and photoelectron-Fenton (PEF) processes were compared in terms of effectiveness and operating costs. In the calculation of costs, various direct cost items including energy, electrodes (cast iron) and H2O2 consumptions were considered. The efficiency of the processes was investigated by changing some operating parameters such as initial pH, initial H2O2 and current. Landfill leachate was used as wastewater in experiments. In terms of costs and the effectiveness, PEF process is clearly preferable; COD removal of the process is 22.5% higher than that of EF process, whereas the total operating costs of both processes are very close to each other.

Key Words: Electro-Fenton, Photoelectro-Fenton, Fenton reagents INTRODUCTION In recent years, an increasing interest has been focused on the application of electrochemically generated Fenton’s reagent (called as electro-Fenton process) [1]. The catalytic effect of Fe2+ in the electro-Fenton process can be enhanced by using UV light. Hence, it is called photoelectro-Fenton (PEF) process that can produce a large regeneration rate of Fe2+. This phenomenon also propagates the oxidative capability of the process due to the rise of the hydroxyl radicals (OH●) in the process. This paper presents a comparison of the PEF and EF processes in terms of operating costs and the effectiveness. In addition, it shows the effects of various operating parameters such as initial pH, initial H2O2 concentration and current on costs. MATERIALS AND METHODS Samples (COD: 2350 mg.L-1) used in the experiments were taken from a landfill area located in Sivas City (Turkey). The EF process was carried out in a glass reactor (1.0 L) equipped with a magnetic stirrer. Two pairs of cast iron anode and cathode electrodes (4x5x0.4 cm) were positioned 1.0 cm apart from each other. The current input was controlled by a DC power supply. In the PEF experiments, ultraviolet (UV) radiation was provided by two UV lamps (4 W). The removal efficiency of the processes was monitored by COD determinations described in Standard Methods [2]. The electrode consumptions during the experiments were determined by using gravimetric method. In the calculations of the costs, the prices of electricity, electrode and H2O2 (35%) were assumed as 0.06 $.kWh-1, 0.3 $.kg-1 and 2.0 $.L-1, respectively. RESULTS AND DISCUSSION The most important items affecting to the operating costs of EF and PEF processes are the consumptions of H2O2, electrode and energy. However, the amount of these items can vary with respect to some operating parameters of the processes such as initial pH, initial H2O2 concentrations and applied current. In this work, several tests were conducted to determine the effects of these parameters on the costs for per kg COD removal, and the results were given in Fig.1. As seen in the Fig. 1, the efficiency of the

49

EF process increases within the pH range 2-3, whereas the effectiveness of the PEF process increases substantially when the current applied to electrodes is increased. In addition, minimum cost of both processes for an acceptable COD removal varies between 2.5$ and 4$ for per kg COD removal from the landfill leachate.

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Fig.1. The effects of the operating parameters of the EF (a) and the PEF (b) processes on the costs of the per kg COD removal.

In order to determine the percents of the cost items within the total costs of both processes, several calculations were done and the results are given in the Table 1. According to the results, the COD removal of the PEF process is 22.5% higher than that of the EF process for initial H2O2: 2500 mg.L-1, whereas the total costs of both processes are much closed. Another important result concluded from the table is that the costs of H2O2 consumptions are 86.9% and 93.2% of the total costs for the EF and the PEF processes, respectively. Table 1. The effects of the cost items on the total costs of the both processes for different H2O2

concentrations (Test conditions; current: 2A, initial pH: 3)

CONCLUSION

Used H2O2 Energy (%) H2O2 (%) Electrode (%) Total cost ($/m3) COD removal (%) (mg.L-1) Photoelectro-Fenton (PEF) Process

1500 6.8 83.3 9.9 8.7 79.4 2000 5.5 85.9 8.5 11.3 85.1 2500 5.1 86.9 8.0 13.9 94.4

Electro-Fenton (EF) Process 1500 6.7 86.9 6.4 8.4 60.8 2000 3.0 91.9 5.0 10.5 70.4 2500 2.7 93.2 4.1 13.0 71.9

Based on the results, it may be concluded that the PEF process can be proposed as a promising approach for treatment of the landfill leachates, when it is compared to EF process. Although, the high operating costs of the PEF process due to high concentrations of used H2O2 limits its commercial usage, it can be applied for the treatment of wastewaters heavily polluted with organic compounds. [1] S. Irmak, H.I. Yavuz, O. Erbatur, Degradation of 4-chloro-2-methylphenol in aqueous solution by

electro-Fenton and photoelectro-Fenton processes, Appl. Cataly. B-Environ. 63(3-4) 2006 243-248. [2] APHA-AWWA-WEF, Standard Methods for the Examination of Water and Wastewater, nineteenth

ed., Am. Public Health Assoc., Washington, DC, 1995.

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New Applications - Bioremediation


ASSESSMENT OF ELECTRODE MATERIALS FOR AN INTEGRATED BIO-ELECTRO-PROCESS

Lohner S.T.a, Becker D.b, Schell H.a, Augenstein T.a, Weidlich C.b, Mangold K.-M.b, Jüttner K.-M.b, Tiehm A.a* aWater Technology Center, Department Environmental Biotechnology, Karlsruher Straße 84, 76139 Karlsruhe, Germany bDECHEMA, Karl-Winnacker-Institut, Electrochemistry and Corrosion, Theodor-Heuss-Allee 25, 60486 Frankfurt am Main, Germany *Corresponding author: E-mail: [email protected] phone: +49(0)721-9678220 fax: +49(0)721-9678101 An integrated Bio-Electro-process for groundwater remediation is developed in order to stimulate microbial degradation of groundwater contaminants by the application of electrodes in the subsurface. The main focus in this project is on chloroethenes as these compounds occur at the most contaminated sites and are known to form groundwater plumes of several kilometres (Wiedemeier et al., 1999; Bradley, 2003).

Microbial degradation of chloroethenes has repeatedly been demonstrated during the last years. The degradation mechanisms comprise (i) anaerobic reductive dechlorination (e.g. halorespiration) of perchloroethene (PCE) and trichloroethene (TCE) with hydrogen as electron donor and (ii) oxidative dechlorination in particular of cis-dichloroethene (DCE) and vinyl chloride (VC) using oxygen as electron acceptor. Under in-situ conditions, a limited availability of electron donors and acceptors results in limited bioremediation efficacy (Tiehm et al., 2002).

The scope of this study was on the selection of a suitable electrode material for electrolytical hydrogen and oxygen formation without undesirable side reactions. For example, previous studies indicated that some side reaction products generated at the electrodes have detrimental effects on microbial VC degradation activity (Lohner et al., 2005). Therefore, inhibiting and competitive reactions such as chlorine formation, nitrate reduction, precipitation of carbonates, and corrosion had to be considered.

Different electrode materials like dimension stable anodes (DSA: titanium with specific oxide coatings), stainless steel, graphite, vitreous carbon and others were tested according to these criteria. The reactivity of the electrode materials was characterized by cyclic voltammetry and by chemical analysis of reaction products (e.g. hydrogen, hydrogen peroxide, oxygen, chlorine) in mineral medium simulating worst case electrolysis conditions (app. 4 mA/cm2 current density, 100 mg/L chloride concentration). The experiments demonstrated that the side reactions differed significantly depending on the material composition of the electrodes.

At the cathode only minor side reactions could be observed, the main reaction was hydrogen production. However, at graphite, vitreous carbon and some DSA electrodes (depending on their coating composition) significant amounts of hydrogen peroxide were detected as these materials have a high overpotential for hydrogen generation. Precipitation reactions at the cathode were detected but did not affect the hydrogen generation efficiency. Nitrate reduction was not observed under the applied experimental conditions.

53

The rate of oxygen generation was similar at most electrode materials. Only at graphite and vitreous carbon very low oxygen formation efficiencies were measured. Chlorine formation and corrosion proved to be the most important anodic side reactions. Chlorine generation was most pronounced at the DSA electrodes and increased with increasing current density and chloride concentration in the electrolyte. Minor corrosion was observed when stainless steel was used as anode material, even at high current densities.

The results show that the selection criteria for a suitable electrode material were best fulfilled with stainless steel electrodes which had a good hydrogen and oxygen generation efficiency and did not show significant chlorine and hydrogen peroxide production. Corrosion can be minimized when using low current densities as they are used in the Bio-Electro-process. DSA electrodes were less suitable because of their high chlorine and hydrogen peroxide formation rates. Vitreous carbon and graphite did not show high hydrogen and oxygen production efficiencies, in addition high hydrogen peroxide concentrations were measured at these materials. In conclusion, stainless steel proved to be the best material for the application in microbiological remediation systems. Therefore this material was used in further studies combining electrolysis with microbial degradation. Acknowledgement: We gratefully acknowledge financial support by the Federal Ministry of Economics and Technology and the German Federation of Industrial Research Associations "Otto von Guericke" e.V. (AiF) (Förderkennzeichen: 150 ZN) [1] Wiedemeier T.H., Rifai H.S., Newell C.J., Wilson J.T. (1999) Natural attenuation of

fuels and chlorinated solvents in the subsurface, John Wiley & Sons, Inc., New York

[2] Bradley P.M. (2003) History and ecology of chlorethene biodegradation: A review. Bioremediation Journal 7(2): 81-109

[3] Tiehm A., Gozan M., Müller A., Schell H., Lorbeer H., Werner P. (2002) Sequential anaerobic/aerobic biodegradation of chlorinated hydrocarbons in activated carbon barriers. Water Science & Technology: Water Supply 2(2): 51-58

[4] Lohner S.T., Tiehm A. (2005) Influence of electric fields on VC dechlorinating microorganisms. In: 5th Symposium on Electrokinetic Remediation (EREM), Fundamental and Industrial Aspects (book of abstracts), Ferrara/Italy, 22-25 May 2005, 40

54


ELECTROKINETIC TRANSPORT AND PROCESSING OF BONE REPAIR AGENTS

Henry E. Cardenasa, Satya S.Vasamb, Yu Zhaob, Deepika Morishettib

aTrenchless Technology Center, Departments of Mechanical and Nanosystems Engineering at Louisiana Tech University, 600 W. Arizona St., Ruston LA, 71272 USA bDepartment of Mechanical Engineering at Louisiana Tech University, 600 W. Arizona St., Ruston LA, 71272 E-mail: [email protected]

ABSTRACT

Calcium phosphate cements (CPC’s) are used extensively for bone replacement due to their similarity to the mineral component of bone. The objective of this work was to demonstrate that CPC particle suspensions can be developed and electrokinetically delivered onto a porous substrate, rapidly increasing the mass and reducing the permeability of the structure. The progression of changes in morphology of the CPC’s observed under the scanning electron microscope (SEM) indicated evidence of bioactivity resulting from exposure to simulated body fluid (SBF). Teflon Millipore filters were used to capture suspended CPC particles as they were undergoing electrokinetic transport. The permeability of the filters was reduced by approximately a factor of 100 after 6 hours of electrokinetic treatment. Weight measurement results showed that the treatment increased the mass of the filters by approximately 64%. This work demonstrated that bioceramic suspensions can be developed and electrokinetically delivered onto a porous substrate, rapidly increasing the mass and reducing the permeability of the structure. Proposed work will focus on electrokinetic delivery of PCP particles within bone tissue that is saturated with SBF. Strength testing will be conducted following an incubation period in order to determine if electrokinetic delivery is feasible.

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ELECTRO-BIOREMEDIATION: INFLUENCE OF DIRECT CURRENT ON THE PHYSIOLOGY AND DISPERSION OF POLLUTANT

DEGRADING BACTERIA IN MODEL SOIL Lei Shi, Susann Müller, Hauke Harms, Lukas Y. Wick UFZ Helmholtz-Center for Environmental Research, Department of Environmental Microbiology, 04318 Leipzig, Germany; E-mail: [email protected] Heterogeneous distribution of hydrophobic organic contaminants (HOC) and HOC-degrading organisms limits the bioavailability and bioremediation efficiency of soil-bound HOC. As a consequence there has been increasing interest in employing electro-bioremediation, a hybrid technology of bioremediation and electrokinetics, to overcome the limited HOC-bioavailability by physically homogenizing both immobilised microorganisms and diffusion-retarded HOC. For in-situ electro-bioremediation small scale dispersion of HOC is intended rather than ‘macroscopic’ HOC-transport (HOC-extraction), as bacteria are ubiquitous in soil. Assuming average separation distances of ≤ 100 microns [1] between individual bacterial microcolonies, short distance transport may drastically improve the contact between pollutant molecules and bacteria and, concomitantly, biodegradation [2]. Present electrobioremediation approaches mainly aim at pollutant transport over large distances and tend to neglect both the impact of direct current (DC) on organism-soil interactions and microscale HOC release rates. Accordingly, few data are available on bioavailability changes acting via DC-driven effects on organism–compound and organism–soil-interactions. However, detailed investigations of the influences of weak electric fields on the relevant bioremediation processes of soil-bound HOC, in particular its influence on microbial physiology and the physico-chemistry of organism–matrix and organism-compound interactions, are scarce [3]. Up to now, investigations of the impact of weak electric fields on microorganism-matrix interactions have solely focused on the electrokinetics-driven bacterial transport in subsurface, as a result of either electrophoretic movement of negatively charged bacteria to anode and/or electroosmotically-stimulated bacterial translocation to the cathode. Detailed studies of population-heterogeneity-based bacterial electrokinetic dispersion, and dispersion-induced bacterial adhesion and cell physiology changes are still missing. Here we present an extended investigation of the role of electrokinetics on bacterial subsurface behaviors, namely population-heterogeneity-based dispersion, adhesion and cell physiology, of fluorene-degrading sphingomonads in bench scale model aquifers filled with glass beads in presence of weak electric field (1 V cm-1). Flow cytometry was applied to quantify the total number of cells, cell size, as well as the propidium iodide (PI) uptake and the DNA-patterns on a single-cell level. Furthermore, as highly transport relevant cell properties, the physico-chemical cell surface characteristics (surface hydrophobicity and charge) were investigated by contact angle and zeta potential measurements. No negative effects of DC on the cells’ physiology were found. During 15.5 h of DC-treatment 57% of all cells recovered were dispersed at the centimetre-scale relative to 27% in the absence of DC leading to an approximately sevenfold enhanced DC-driven homogenization efficiency relative to bacteria dispersed by bulk random motility only. Interestingly however, cells mobilised by electrophoresis and electroosmosis exhibited significantly changed adhesion

57

properties. No overall negative effect of DC on the cell viability was found as 6.8% of the DC-treated bacteria exhibited PI-staining relative to 6.0% in the control. Minor differences however were observed in the sub-population that had been mobilised by electroosmosis exhibiting an about two-fold increased PI-% relative to the control. Enhanced PI-staining however did not correlate with reduced culturability of the cells on rich medium agar plates; Relative to the control DC-treated cells mobilised by electroosmosis were even three-fold more culturable and confirm earlier data that PI-permeability does not always indicate reduced viability of oligotrophic environmental bacteria [4]. Our findings thus suggest that electroosmosis is a valuable mechanism to transport viable and culturable PAH-degrading bacteria in the subsurface. Whereas our studies have demonstrated an effective DC-driven homogenization of physiologically active bacteria on the mesoscale, the main thrust of our ongoing research lies in the investigation of the electrokinetic influence at the microscale, i.e. the homogenization processes at the soil pore-water interfaces. [1] T.N.P. Bosma, P.J.M. Middeldorp, G. Schraa, A.J.B. Zehnder, Environ. Sci. Technol. 31 (1997) 248. [2] K.T. Semple, A.W.J. Morriss, G.I. Paton, Europ. J. Soil Sci. 54 (2003) 809. [3] L.Y. Wick, L. Shi, H. Harms, Electrochim. Acta. 52 (2007) 3441. [4] L. Shi, S. Günther, T. Hübschmann, L.Y. Wick, H. Harms, S. Müller, Cytometry A (2007), in press.

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ELECTROKINETIC REMEDIATION OF BIOSOLIDS THROUGH INACTIVATION OF Clostridium perfringens SPORES

Maria Elektorowicza, Elham Safaeia, Jan Oleszkiewiczb, Robert Reimersc

aConcordia University (EV6.139), 1455 de Maisonneuve Blvd. W., Montreal, Quebec, H3G 1M8 Canada, E-mail: [email protected] bUniversity of Manitoba, School of Engineering, Winnipeg, Canada, R3T 5V6 cTulane School of Public Health and Tropical Medicine, New Orleans, LA, USA Municipal wastewater treatment facilities convert soluble organics into biosolids. Millions of tons of this nutrient-rich material are being added to soil each year. The governmental agencies in North America encourage biosolids recycling. US EPA (40 CFR Part 503) regulations for the use and disposal of sewage sludge, defines two types of biosolids with respect to pathogen reduction: Class A and Class B. Class A biosolids can be applied in the same way as commercial fertilizer, without the restrictions that govern Class B sludge. Class A status can be achieved by decreasing helminthes, viruses and pathogenic bacteria counts below threshold levels or maintaining certain conditions of e.g. time, temperature or pH.

A considerable effort has been made to identify indicator microorganisms whose presence would suggest that human pathogens might also be present. Clostridium perfringens has been suggested as a better indicator organism to assess the efficiency of biosolids disinfection while screening for parasites that may or may not be present. C. perfringens is a spore-forming thermophilic bacterium and has been suggested as an indicator for inactiavtion mechanisms other than temperature (as it is resistant to temperature). This organism is found in densities of 106 colony forming units (CFUs) per gram of solids in raw biosolids and has been suggested as an excellent surrogate for the Ascaris ova in biological systems such as composting and anaerobic digestion. C. perfringens spores exhibits similar resistance to physical and chemical agents and is hardier than Ascaris in high temperatures.

Our previous research showed that Electrokinetics (EK) successfully inactivate total coliforms (TC) in sewage sludge; the aim of this study was to examine the impact of EK on C. perfringens vis a vis criteria for Class A biosolids. In order to assess different stressors affecting the inactivation of C. perfringens, series of electrokinetic cells, filled with anaerobically digested sludge were investigated in bench scale in an attempt to simulate possible future full scale process.

A number of factors including electric field strengths, enhancement of oxidizing conditions, duration of exposure, and response to different conditioners were investigated. The pH, electrical parameters, as well as quality of catholyte and anolyte were measured daily. Total volatile fatty acids, total solids content, phosphorus and nitrogen compounds were analyzed after each treatment. The enumeration of the fecal coliforms (FC) and spores of C. perfringens in treated sewage sludge was carried out by M-CF method and non-commercial Tryptose-sulfite-cycloserine (TSC) agar culture medium, respectively.

Result showed a relationship between C. perfringen inactivation and type of oxidants, pH gradient, and electric field strength. A decrease in volatile solids, nutrients and phosphorus contents were observed in all electrokinetic cells. No viable FC was observed in treated sludge. The electrokinetic method was demonstrated to be a successful technique for biosolids disinfections.

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ELECTROKINETIC ENHANCEMENT OF PHYTOREMEDIATION IN Zn Cd Cu AND Pb CONTAMINATED SOIL

USING POTATO PLANTS R. Bi, H. Aboughalma, M. Schlaak Institute of Environmental Technology (EUTEC), University of Applied Sciences FHOOW, Constiaplatz 4 D-26723 Emden, Germany E-mail: [email protected]

Introduction As a result of industrialisation an increasing number of sites are contaminated by

heavy metals. Phytoremediation describes the biological process of using plants to remove such contaminants from soil. To be effective the plants must withstand uptake of heavy metals in the root system, translocate metals to the above ground plant parts and accumulate them in the biomass[1]. Due to the long remediation time expected for phytoremediation, methods of enhancement are needed. Electrokinetic effects might be a potential method of enhancement both for bioremediation with bacteria[2] and for phytoremediation of heavy metals [3].

Method The combination of electrokinetics with phytoremediation to decontaminate heavy

metal polluted soil has been demonstrated in laboratory-scale experiments.

Figure 1: Experiment set up with potato plants under three different treatments

Nine potato tubers were planted in nine experimental vessels (each 340 x 340 x 280 mm) filled with soil from a cultivated area near a metal smelter in Nordenham/Germany. The experiment was conducted in a chamber under artificial light at the University of Applied Sciences in Emden/Germany. Thirty days after the tubers were planted, direct current (DC) was applied in three vessels, and alternating current (AC) was applied in another three vessels. Three vessels without electrical fields were used as the control (figure 1). The electrical fields were applied for 60 days and the current was kept about 500 mA until harvesting. The soil profiles were investigated for one of the AC and one of the DC vessels. Plant physiological parameters, such as water content, chlorophyll content and biomass production were determined. The metal content of the soil and

61

plant samples were determined by flame AAS after microwave digestion. The pH in the soil profile samples was determined using a pH meter.

Result and Discussion The water content and the chlorophyll content of leafs of plants growing under the

electrical field (AC and DC) were higher than those without electrical treatment. The biomass production of the plants growing under AC treatment was the highest at 1.8 kg, followed by the control plant at 1.0 kg, and the plant growing under DC treatment at 0.75 kg.

Figure 2: Metal content in the potato plants under three different treatments

The plants growing under AC treatment had the highest metal content (Cu, Cd, Pb and Zn) compare to those under DC treatment or the control. When the biomass production and the metal contents are combined, the AC field showed the highest enhancement of phytoremediation.

The plants growing under the DC treatment showed the lowest biomass production, Cd and Pb contents. This could be explained by the observed change of pH condition (3.8 near anode and 7.8 near cathode), resulting in inhibition of plant growth and metal uptake. Never the less, there was a higher Zn and Cu content in the plant under DC treatment than in the control plant.

Conclusion Combination with electrical field application, especially using alternating currents,

represents a promising approach to enhance the decontamination of metal polluted soils using phytoremediation. The application of direct current field requires optimisation in order to overcome the lower pH conditions induced and resulting phytotoxicity and potential metal mobility. [1] I. Raskin and B. Ensley (1999). 2nd Ed Phytoremediation of Toxic Metals: Using plants to Clean Up the Environment. Wiley & Sons. [2] Luo Q S, Zhang X, Wang H and Qian Y, (2005). Journal of Hazardous Materials B121: 187-194. [3] O’Connor C S, Lepp N W, Edwards R and Sunderland G, (2003). Environ. Moni. And Ass. 84: 141-158.

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TETRACHLOROETHYLENE BIOREMEDIATION BY ELECTROCHEMICAL INJECTION OF AN ELECTRON DONOR

Xingzhi Wu a, David B.Gentb, Akram Alshawabkeha Jeffrey L. Davisb

aDept. of Civil and Environmental Engineering, 400 Snell Engineering Center, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA bEnvironmental Laboratory, USACE Engineer Research and Development Center, 3909 Halls Ferry Road, Vicksburg, MS 39180 USA Tel. 601 634 4822 Fax. 601 634 3518 E-mail: [email protected] Introduction. Bioremediation of tetrachloroethylene (PCE) by reductive dechlorination has been successful when an electron donor such as lactate has been made available to microorganisms. In heterogeneous PCE contaminated aquifers, uniform delivery and mixing of electron donor amendment have met limited success because the electron donors cannot be delivered into the low permeable zones. Electrochemical amendment injection provides an alternative to hydraulic methods by delivering the electron donor to microorganisms in the low permeable zones where hydraulic delivery fails. Methods and Materials. A series of experiments evaluated the efficacy of lactate amendment injection and the remediation of PCE under hydraulic and electrochemical conditions into a low permeable silty clay (kh = 2×10-7 cm s-1). Lactate injection experiments were conducted in clay and heterogeneous soil under 1.2 A m-2 and 5.3 A m-2 current densities. Additional experiments mixed Dehalococcoides KB-1™ microbial culture (SiREM, Ontario, Canada) with PCE (20 mg L-1 in the pore water) in a clay-water slurry and consolidated the slurry into 40-cm long cells placed inside a nitrogen filled anaerobic chamber. Duplicate experiments with the PCE/KB-1™ mixture were operated as control (no electricity applied) and duplicate PCE/KB-1™ mixture bioremediation experiments were conducted under 5.3 A m-2 and 13.3 A m-2 current densities (Figure 1). Results and Discussion. Results from electrochemical injection experiments show the most effective injection of lactate was achieved under the higher current density of 5.3 A m-2. The resulting electroosmotic and ion migration transport rates averaged 2.16 cm2 V-1 d-1 and 3.4 cm d-1, respectively. Pore water lactate concentrations as high as 800 mg L-1 were detected in the clay pore water (Figure 2a). The ion migration rate was more than 191 times faster than transport under a hydraulic gradient. Well bio-fouling observed in the hydraulic delivery experiments was not detected under those using electrochemical injection. Conclusions. The PCE and the KB-1™ culture mixed (no electricity) with the clay resulted in PCE dechlorination halting at cis-DCE presumably by lack of an electron donor (Figure 2b). The duplicate PCE and KB-1™ culture experiments with lactate injection by electrochemical means completely degraded PCE to ethene within 4 months across the 40 cm long silty clay sample. PCE was transformed to DCE following a zero order rate of 0.0063 to 0.027 mmol L-1·d-1 (Figure 2d) and DCE to ethane followed a first order rate of 0.0577 to 0.254 d-1. The soil pH remained between 7 and 7.5 throughout the experiment (Figure 2c).

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Figure 1. Schematec of Electrochemical Injection System.

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EC-A EC-B

(a) electrochemical injection

6.8

6.9

7.0

7.1

7.2

7.3

7.4

7.5

7.6

0 10 20 30 40 50

Distance from Anode (cm)

pH

EC-A EC-B Control A

(c)

Figure 2. Results from biological experiments (a) DCE in control, (b) DCE in electrochemical injection (EC-1), (c) Final pore water lactate (d) Final pH of Electrochemical (EC)and Control A

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Organic Pollutants


INFLUENCE OF ELECTROOSMOTIC FLOW ON THE PAH RELEASE FROM MODEL SOIL MATRICES

Lei Shi, Hauke Harms, Lukas Wick UFZ Helmholtz-Center for Environmental Research, Department of Environmental Microbiology, 04318 Leipzig, Germany; E-mail: [email protected] The basic principles of electrokinetic extraction and the electrokinetically enhanced bioremediation of contaminants from fine-grained soil have been experimentally proven to be feasible. Although empirical electro-bioremediation appears to be safe, effective and economically interesting compared to other remediation techniques there is still a need for mechanistic understanding of the molecular processes affecting the release and transport of hydrophobic organic contaminants, such as polycyclic aromatic hydrocarbons (PAH) in soil. Due to their hydrophobicity PAH are mainly dissolved in non aqueous liquids (NAPL) or associated with the surface or the intra-particle pores of the solid phase in soil. Limited release of PAH has been proven to dramatically decrease the PAH-bioavailability, and consequently the efficiency of bioremediation. The release rate of PAHs from the solid to the aqueous phase is limited by the slow diffusion through the unstirred boundary layer around soil particle [1] or the stagnant water phase in intra-particle nanopores. Electroosmotic flow (EOF) is used in capillary electro-chromatography (CEC) as a pumping aid instead of hydraulic flow (HF) to enhance mass transfer of solute between mobile and stationary phase [2]. Based on the knowledge from CEC, we hypothesize that EOF is likely to overcome mass-transfer bottlenecks in low permeable soil matrices by i) increasing the release of sorbates by inducing liquid flow at the immediate exterior of soil particles, ii) creating flow in nanopores in the organic sorbent phase, which are inaccessible by hydraulic flow, and iii) influencing the pore or surface diffusion among aggregated minerals [3]. Here we present an investigation of the effect of EOF on the dissolution and release of surface- and intra-particle-bound phenanthrene using well defined model aquifers of known solid matrix structures (e.g. alginate beads). EOF-facilitated PAH release was compared to the PAH release in presence of HF of similar flow rates (1 mL h-1). Our data indicate an approximately fourfold enhanced EOF-induced release of phenanthrene from alginate beads. This effect is explained by a (theoretically expected) significantly decreased thickness of effective diffusion layer of phenanthrene. Ongoing research focuses on EOF-facilitated phenanthrene release from intra-particle nanopores of well defined model aquifers with high tortuosity.

[1] P. Mayer, U. Karlson, P. Christensen, A. Johnsen, S. Trapp, Environmental Science and Technology 39 (2005) 6123. [2] M. M. Robson, M. G. Cikalo, P. Myers, M. R. Euerby, K. D. Bartle, Journal of Microcolumn Separations 9 (1997) 357. [3] L.Y. Wick, L. Shi, H. Harms, Electrochimica Acta 52 (2007) 3441.

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ELECTROKINETIC REMOVAL OF MOLINATE FROM SOILS: EXPERIMENTAL AND MODELING

A. B. Ribeiro1*, J. S. Santos1, E. P. Mateus1, J. M. Rodríguez-Maroto2, M. D. R. Gomes da Silva3, L. M. Ottosen4 1Departamento de Ciências e Engenharia do Ambiente, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal 2Departamento de Ingeniería Química, Facultat Ciencias, Universidad de Málaga, Campus de Teatinos, Málaga 29071, España 3 REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal 4 Department of Civil Engineering, Kemitorvet, Building 118, Technical University of Denmark, DK-2800 Lyngby, Denmark *Tel: (+351) 212 948 300 – Fax: (+351) 212 948 554 – E-mail: [email protected]

Abstract The contamination of soils, groundwater, and surface waters by chemicals used in agriculture is currently a significant concern. Many of these agrochemical compounds are considered a threat both to the environment and to biota. Molinate (S-ethyl N,N-hexamethylene-1-carbamate), an herbicide, is applied once a year to flooded fields during rice seeding to control the overgrowth of weeds. The removal of molinate was studied when submitted to an electric field. The applicability of the electrokinetic process in molinate soil remediation was evaluated. Two soils were used, being one of them spiked with molinate residues. Several electrokinetic experiments were carried out at a laboratory scale. Determination of molinate residues were performed by chromatography and mass spectrometry. The results show that the electrokinetic process is able to remove molinate in soil solution. A one-dimensional model was developed for simulating the electrokinetic treatment of a saturated soil containing molinate. The movement of molinate was modelized taking into account the diffusion transport resulting from molinate concentration gradients and the eventual reversed electroosmotic flow at acidic soil pH.

Keywords Electroremediation, herbicides, modeling, soil

69


REMEDIATION OF HEXACHLOROBENZENE IN SOIL BY ENHANCED ELECTROKINETIC FENTON PROCESS

Oonnittan, A., Shrestha, R., Sillanpää, M. University of Kuopio, Laboratory of Applied Environmental Chemistry, P. O. Box 181, FIN-50101 Mikkeli, Finland. Tel.: +358449102136; fax: +358153556513; E-mail: [email protected]

1 Introduction Pollution of sites by persistent organic pollutants (POPs) has always been an issue of major concern among the international community because of the threats they pose to the environment. Though various conventional physical, chemical and biological techniques are available for the treatment of contaminated sites, they have proved unsuccessful to remediate soils of low permeability contaminated with compounds of low water solubility like POPs.

Recent research has shown that Electrokinetic remediation is a promising technology for remediation of soils of low permeability [1]. Electroosmosis is the major mechanism by which POPs are transported through the soil matrix during their electrokinetic treatment. To enhance the solubility and mobility of these contaminants, surfactants can be used. To prevent further treatment of the waste water collected from the electrokinetic system, it can be integrated with Fenton’s process.

In this study, the performance of enhanced electrokinetic and electrokinetic fenton treatment of soil contaminated with persistent organic pollutants is investigated by selecting hexachlorobenzene (HCB) as the model compound.

2 Materials and Methods The electrokinetic laboratory apparatus used consisted of two electrode compartments with a soil chamber in between. The cell was made of glass and the dimension was 35 × 17 × 25 cm. Filter cloths were inserted between the chambers to separate the soil mass from getting mixed with the anodic and cathodic solutions. Soil samples were collected on a daily basis and analyzed for HCB using gas chromatography (Agilent Technologies 5975). Table 1. shows the experimental conditions for tests 1, 2 and 3.

3 Results and Discussions Figures 1 and 2 show the concentration of HCB in soil with elapsed time for electrokinetic treatment of soil for tests 1 and 2. Test 2 shows higher contaminant removal. This is because of the use of cyclodextrin, which solubilised the HCB sorbed to the soil and also due to the increased electroosmotic flow rate. Elevated electroosmotic flow indicates increased soil- contaminant-solution interaction. Figure 1 indicates that in test 1 during the electrokinetic process, no significant contaminant movement occurred. This is because of low aqueous solubility of hexachlorobenzene. The uneven distribution of contaminant in figure 1 occurred due to the washing and subsequent accumulation of contaminant particles attached to the surface of soil particles. Figure 3 shows that significant reduction in the contaminant concentration has occurred as the result of electrokinetic fenton treatment of the soil.

71

Table. 1 Testing Program Test Soil Contaminant Anodic solution Cathodic

solution Voltage Volts

Total duration (hrs)

1 Kaolin HCB 0.01 M KCl Deionized water

15 5 x 24

2 Kaolin HCB 1 % Cyclodextrin solution

Deionized water

15 5 x 24

3 Kaolin HCB Ferrous sulphate, 1%cyclodextrin and 5% hydrogen peroxide

Deionized water

30 10 x 24

HCB in soil mg/kg

0

5

10

15

20

24 48 72 96 120

hours

HC

B in

soi

l mg/

kg

Concentration of HCB in soil mg/kg

0

10

20

30

40

50

24 48 72 96 120

hours

HCB

in s

oil m

g /k

g

Figure 1 : Concentration of HCB in soil Figure 2: Concentration of HCB in soil with elapsed time for test 1 with elapsed time for test 2

Distribution of HCB in soil at different sections with elapsed time

050

100150200250300350400450500

1 2 3 4 5 6 7 8 9 10 11 12

Elapsed Time (days)

HCB in

soi

l (m

g/kg

)

Anode

Middle

Cathode

Figure 3 : Distribution of HCB in soil at different sections with elapsed time.

References [1] Chang, J.H., Qiang, Z, and Huang, C.P. 2006. Remediation and simulation of selected chlorinated organic solvents in unsaturated soil by a specific enhanced electrokinetics. Colloids and surfaces A: Physiochem. Eng. Aspects, Volume 287, Issues 1-3, 15 September 2006, Pages 86-93

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INTEGRATED ELECTROKINETIC PROCESS WITH BDD ELECTRODE FOR DEGRADATION OF PHENOL FROM

CONTAMINATED SOIL You-Jin Lee, Jong-Young Choi, Ji-Won Yang* Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), 373-1 Guseong-dong, Yuseong-gu, Daejeon, 305-701, Republic of Korea E-mail: [email protected] 1. Introduction Boron-doped diamond (BDD) electrode has received a great attention as a new anode material in an advanced electrochemical oxidation process because of its extremely wide electrochemical potential window and inert surface [1]. Many papers have reported that various organic contaminants, such as phenols [2] and dyes [3], are completely oxidized during electrolysis by BDD electrode. In this study, a new integrated electrokinetic process was proposed using BDD electrode as anode. It can not only separate organic contaminants from soil by inducing electrokinetic phenomena but also mineralize them electrochemically by producing oxidants on the surface of BDD electrode. To investigate the feasibility of the integrated process, electrokinetic tests using BDD electrode were performed for the remediation of phenol-contaminated soil and the results were compared with those of simple electrokinetic tests.

2. Materials and methods

For the test, surface soil (< 1.00 mm) was artificially polluted with phenol and the initial concentration was about 200 ppm (mg/kg dry soil). A rectangular reactor (5*5*20 cm3) was used for both simple and integrated electrokinetic tests. It has a 10 cm-long soil compartment and two electrode chambers (100 mL) placed at each end.

In integrated electrokinetic tests, BDD coated Niobium plate electrodes (Nb/BDD, 40*40*2 mm3) purchased from Fraunhofer IST (Germany) were used for anode and platinum coated stainless steel (S.S./Pt) electrodes were used for cathode. To enhance the electrochemical oxidation of organic pollutant in anode compartment, the effluent drained out from cathode reservoir by electroosmosis was circulated to anode reservoir. For a comparative purpose, simple electrokinetic tests were also conducted using S.S./Pt electrodes for both anode and cathode. A DC electric current was applied under the constant current condition, 10 mA or 20 mA, and 0.05 M K2HPO4 was used as an electrolyte.

During the operation period, the variation of electric potential was observed and the phenol concentration in electrode reservoirs was measured periodically. After 10 days, to evaluate the removal efficiency, the residual amount of phenol in electrokinetic reactor was analyzed for each compartment: anode and cathode reservoirs, 10 sections of soil specimen, and effluent.

[1] M. Panizza, G. Cerisola, Electrochim. Acta 51 (2005) 191. [2] P. Canizares, J. Lobato, R. Paz, M. A. Rodrigo, C. Saez, Water Res. 39 (2005) 2687. [3] X. Chen, G. Chen, Sep. Purif. Technol. 48 (2006) 45.

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3. Results and discussion The electric potential in the integrated system using BDD electrode changed just like that in the simple electrokinetic test. The power consumption was, therefore, almost same for 10 days and was only influenced by the applied current: about 40 and 180 Wh were used for 10 and 20 mA tests, respectively.

In general, the velocity of electroosmotic flow is proportional to potential gradient. The higher current was applied, the more electroosmotic flow was produced. In the simple electrokinetic tests, the removal efficiency of phenol was affected by the accumulated amount of electroosmotic flow because phenol is relatively soluble in water. In the test of 20 mA, most of phenol was removed from soil and only 2.1 % remained.

When BDD electrode was employed as anode in electrokinetic process, the residual amount of phenol in soil was almost same as that of the comparative test. While most of phenol was contained in effluent in the simple electrokinetic test, the contaminant was effectively degraded in the integrated process: 56.7 and 90.3 % of phenol were oxidized in the tests with 10 and 20 mA, respectively. It demonstrates that the integrated electrokinetic process with BDD electrode can effectively degrade organic contaminants from soil by controlling current density and operation time.

Phenol content (%)

0 20 40 60 80 100 120

Anode reservoirSoilCathode reservoirEffluent

Reactor 1(10 mA)

Reactor 2(20 mA)

22.3 8.9 81.5

96.3

2.1 2.0

(a)

Phenol content (%)

0 20 40 60 80 100

Anode reservoirSoilCathode reservoirDegrdationLoss by sampling

Reactor 1(10 mA)

Reactor 2(20 mA)

24.3 5.8 56.7

90.3

0.7

13.2

9.0

(b)

Figure 1. Phenol content in electrokinetic reactor after the operation: (a) simple electrokinetic process and (b) integrated electrokinetic process with BDD electrode.

4. Conclusions In this study, the integrated electrokinetic tests using BDD electrode were conducted for the remediation of phenol-contaminated soil for 10 days. Most of phenol was transported toward cathode by electroosmosis and then degraded near the anode compartment of BDD electrode by circulating effluent. The consumed electricity during the operation time was similar to that of the simple electrokinetic test.

From the results, it can be concluded that the integrated electrokinetic process is feasible for the treatment of contaminated soil with organic pollutants. It might be an innovative in-situ soil remediation technology to make up for the weak points of electrokinetics such as anode corrosion and effluent treatment.

Acknowledgement This subject is supported by Korean Ministry of Environment as "The Eco-technopia 21 project".

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ELECTROKINETIC REMEDIATION OF THE OIL-CONTAMINATED SOILS

V. A. Korolev, O.V. Romanyukha & A.M. Abyzova Russia, Moscow, Geological Faculty of MSU named M.V. Lomonosov E-mail: [email protected]

One of the widespread consequences of industrial activity is the pollution of a soil cover by oil and the products of their processing. On a modern level of development of the oil-extracting industry to exclude its influence on an environment it is impossible. Soils the first perceive oil pollution at its floods and failures. In connection with this appears the need of developing of new and perfection of the existing technologies of the restoration of the oil-contaminated soils. One of perspective directions of the remediation of the oil-contaminated soils is use of an electrokinetic method.

In the given report results of research of the factors influencing on efficiency of electrokinetic clearing of soils from oil pollution are stated.

In the course of a study the following factors, which influence on the electrokinetic cleaning efficacy: the property and the genetic special features of soils, the grading of soil, the mineral chemical composition and the concentration of the soil pore solution, the composition of oils and the processes of the natural degradation of oil. By the results of experiments the dependences reflecting influence of these factors on the electrokinetic clearing efficiency have been received.

Researches of the electrochemical migration of oil under the action of direct electric current were accomplished by us both on the model and natural soils of different genetic accessory. In total it has been selected and analyzed twelve versions soils of five genetic types. As the object of researches have been chosen: the chernozem southern, ordinary, leached and typical, the grey wood, light grey wood, dark grey wood, the podzol and sod-podzol, the alluvial-grass and the peat ground. Model samples were prepared from the pastes, whose initial moisture corresponded to the upper plastic limit. To the natural and model samples was added a known quantity of oil, which then was moved away from the model with the aid of the action of the field of direct electric current.

The laboratory study of the electrokinetic soil decontamination from oil was performed in the electro-osmotic cells. In that version, a 10-cm long and 2,5-cm diameter tube was used as a cell, to the ends of which direct current was applied. Platinum electrodes were mounted at the tube ends, contacting with the sample. During the experiment, current was applied to the soil sample for 4 to 6-8 hours. Then the collected filtrate was analyzed, and the sample was cut lengthwise in sections with subsequent moisture, pH and residual oil content determination for each section.

In this series of experiments it was possible to establish the leading factors influencing process of electrokinetic clearing of soils from oil pollution. In all studied soil samples the movement of oil with an electroosmotic stream of water was observed. As a result of it one of near-electrode parts of the sample was cleared of oil, and another was enriched. Thus it is established, that in a floor of a constant electric current the oil moves to the cathode, carried away owing to viscous friction a water solution.

Since this method is based on the removal of liquid hydrocarbon pollution under the action of DC field with aid of the electroosmosis, that nature and intensity of this process in many respects is determined by the same factors, which influence the special feature of the structure of dual electrical layer (DEL).

The results of studies showed that the intensity of the migration of oil grows with an increase of the quantity of clay minerals in the soil and the decrease of the content of

75

water-soluble salts, since, other conditions being equal, in this case grows the thickness of diffuse DEL, and, therefore, and the speed of electrical osmosis transfer. Furthermore, the obtained data about the efficacy of electrokinetic cleaning clearly correlate with the physicochemical indices of the investigated soils.

The influence of composition and concentration of the electrolyte of the pore solution of soils on the efficacy of electrokinetic cleaning also is reflected in the structure DES. To analyze the relationship between decontamination efficiency of oily soils and concentration of the alkaline solution in pores, NaOH solutions with concentrations of 0.01, 0.05, 0.1 и 0.25 N, HCl in those concentrations and 0,01 N NaCl were used. The results of studies shows that with an increase in concentration HCl, occurs reduction in the effectiveness in the cleaning, and with the use of solution NaOH as the pore was obtained inverse dependence. Partial solubility of oil in alkali possibly promotes more efficient oil removal from the sample containing NaOH. Apparently, a part of hydrocarbon contaminant dissolves due to the electrokinetic inter-reaction with the alkali solution.

With the analysis of the influence of grading of soil on the efficacy of the electrokinetic cleaning of the oil-contaminated soils it is established that the content of the particles, which relate to the fraction > 0,01 mm in quantity 55-75%, is optimum relationship for conducting the electrokinetic cleaning. In this case the effect of cleaning soil of about 40% is achieved. With further increase in the content of the particles of these fractions the effectiveness of cleaning is reduced.

To analyze the relationship between decontamination efficiency of oily soils and fractional composition of oil Usinsk's, Tarasovsk's, Yaregsk’s oil, and also the mixture of the crude oil of West Siberia were used. The results of studies showed that the maximum effect of removal is achieved at removal of light Tarasovsk's oil from soil, and minimum from heavy Yaregsk’s oil and composes 43% and 29% respectively.

The study of the influence of the processes of oil degradation on the efficiency of cleaning they showed that the general effect of cleaning decreases with an increase in the period of pollution. In the conducted investigations the period of petroleum pollution varied from 2 of days to 7th months. The analysis of the obtained results showed that the greatest effect of cleaning - 68% is achieved at the electrokinetic working 2 of day pollution, and with cleaning of models 6 and by the 7 of monthly pollution the degree of cleaning composes only 1-2%. Thus, the received results show that the petropolluted file is more senior, the method will be less effective.

Thus, researches carried out by us showed the high efficiency of electrokinetic removal of the petroleum pollution from soils. The studied factors influencing electrokinetic clearing, will allow to understand mechanisms of removal of oil pollution under action of a constant electric current and to develop industrial technology of soil clearing.

References [1] Korolev V.A. et al. (2000). The electrochemical remediation of soils. - Proc. of 31st Internat. Geological Congress, Sess.22-3. – August 6-17, 2000, Rio-de-Janeiro, Brazil (СD-ROM) [2] Korolev V.A. (2001). Laws of the electrochemical soils remediation from petroleum pollution. – EREM 2001. 3rd Symposium and Status Report on Electrokinetic Remediation / Schriftenreihe Angewandte Geologie Karlsruhe, 63, 19 (1-12) [3] Korolev V.A. (2001). The Cleaning of Soils from Pollution. – Moscow, MAIK/ Interperiodica publishing house, 365 pp. (in Russian);

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Modelling and other Applications


PREDICTION OF THE PERFORMANCE OF EKR BASED ON SPECIATION ANALYSIS AND MATHEMATICAL MODELING.

C. Vereda-Alonso, A. García-Rubio, C. Gómez-Lahoz, J. M. Rodríguez-Maroto and F. García-Herruzo Dpto. de Ingeniería Química. Fac. de Ciencias. U. de Málaga. 29071-Málaga (Spain). [email protected] Although some considerations about the future use of a contaminated site may be done, both, the legal definitions to consider it contaminated and remediated, are usually based on the total concentration of regulated toxics. Nevertheless, there is a general agreement to consider that the development of tools for a reliable risk assessment would be desirable so that regulations are based on these risk evaluations. These tools are usually related somehow to bioavailability considerations, but those that have more chances to be used in regulatory texts should be performed using simple and reproducible analytical procedures. Among these techniques a sequential extraction procedure which has a good acceptance among researchers have been used for the speciation of soils contaminated with heavy metals for the determination of their mobility (1). The technique provides four fractions, which here are denominated weak acid soluble (WAS), reducible, oxidizable and residual. On the other hand it is well known that, at a specific contaminated site, the performance of Electrokinetic Remediation (EKR), as happens with all other in situ techniques, is depending heavily on the nature of both the contaminants and the soil. Up to the present moment, few publications have studied the relationship between the maximum remediation that can be achieved and the mobility of the soils as determined by the speciation analysis. For instance, at the contamination case of the Aznalcollar spill (2), it was shown that the speciation of the toxic cations present indicates that their mobility was rather different, as can be seen in figure 1a. It was also shown that, for each metal present, there seems to be a relationship between the maximum remediation that can be achieved by an acid enhanced EKR and the amount initially present as WAS (Fig. 1b).

0

20

40

60

80

100

WAS Reducible Oxidizable Residual

(%)

Cd Cu Fe Pb Zn

a

0

20

40

60

80

100

0 300 600 900 1200 1500t (h)

% re

cove

red

CdZnCuFePb

b

Figure 1. Results for the Azanalcollar spill. a) Speciation analysis. b) Recovery by acid-enhanced EKR.

Regarding that work it was also shown that a mathematical model, with relatively simple transport equations and few equilibrium equations with definitions based on the speciation analysis, was able to describe satisfactorily the behavior of the main parameters of the system. These are the rate of recovery of the toxic ion, the maximum recovery, the rate of acid addition and the energy requirements.

79

Nevertheless, it is clear that more field cases should be studied before a relationship can be accepted between the results obtained from the speciation analysis and the remediation degree achievable by EKR. It is also important to determine a) if for those cases for which other enhancements are used (for instance the use of chelating agents instead of acid enhancement) a relationship between the speciation analysis and the maximum remediation efficiency can be also established. And b) if the toxic ions remaining in the soil after the remediation are those fractions which are less mobile. This is important if in the future EKR is to be accepted by the regulatory agencies even if only a certain amount of the toxic ions can be removed. Regarding these two issues we have initiated a research for the study of remediation alternatives for a soil contaminated mainly with Hg. The site is located close to Almadén (Ciudad Real, Spain), and near the mines that have been producing important amounts of mercury for centuries. After carrying out the speciation analysis, our first approach was to determine the fraction of Hg removable by a flushing solution with iodide. We also performed a speciation analysis after the remediation to determine which fraction was more efficiently removed. Our results are indicating that, approximately, a 30 % of the initial metal concentration can be removed at an acceptable rate. Larger amounts can be achieved but with very little concentration in the effluent. A somewhat surprising result was that the total amount of the more mobile fraction (WAS fraction) was not smaller after the remediation. In fact, the one with a more important decrease after the extraction was the reducible one, whereas the WAS fraction increased five fold. Therefore, even if a fraction of Hg was removed, an increase of the hazards of the site could be derived from the remediation procedure. Similar phenomena have been observed before (3). Of course, the effluent concentration could be limited by kinetic phenomena that can be due to several factors such as the rate of dissolution of the different mercury species present in the soil, or to preferential pathways arising during the remediation for the flushing solution. Alternative remediation techniques should be studied for this site, among which EKR enhanced with iodide presents interesting possibilities, and we are accomplishing that work. Of course, variations on the mobility after the remediation would be also studied, and compared with those observed for the flushing approach. Acknowledgements: This research was funded by Project 148/2004/3 (Ministry for Environment). CGL and CVA acknowledge the economic support from the Junta de Andalucía through the program “Medidas de Impulso de la Sociedad del Conocimiento en Andalucía” References: 1.- A.M. Ure, P. Quevauviller, H. Muntau and B. Griepink, “Speciation of heavy metals in soils and sediments. An account of the improvement and harmonization of extraction techniques undertaken under the auspices of the BCR of the commission of the European Communities”, Int. J. of Environ. and Anal. Chem. 51 (1-4) 135-51 (1993). 2.- M.D. Garcia-Gutierrez, C. Gomez-Lahoz, J.M. Rodriguez-Maroto C. Vereda-Alonso and F. Garcia-Herruzo. “Electrokinetic remediation of a soil contaminated by the pyritic sludge spill of Aznalcollar (SW, Spain)” Electrochimica Acta 52, 3372-3379 (2007) 3.-A.B. Ribeiro and J. M. Rodriguez-Maroto “Electroremediation of heavy metal contaminated soils. Processes and application”. Chap. 18 in Trace elements in the environment CRC Press (2006).

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ELECTROKINETIC REMEDIATION MODEL: ELECTRIC RESISTIVITY HEATING WITH DC ELECTRIC FIELDS

Zorn, R.a, & Steger, H.baEuropean Institute of Energy Research, University Karlsruhe, Emmy-Noether-Strasse 4, D-76131 Karlsruhe, Germany; bDepartment of Applied Geology, University Karlsruhe, Kaiserstrasse 11, D-76128 Karlsruhe, Germany; E-mail: [email protected] The input of electric work during electroremediation leads often to an increase of the in-situ soil temperature. It is well known that a heating up of soil can be reached if a dc electric field is applied to a soil (e. g. MITCHELL 1993). The rise in temperature is mainly caused by a partial conversion of electric energy into joule heating. The electrokinetic remediation is therefore a form of an Electrical Resistivity Heating (ERH) up technology. The increase in temperature raises the vapor pressure of volatile and semi-volatile contaminants, thus increasing their volatilization and removal from the soil. A significant rising up of temperature during electroremediation field scale tests are e.g. described by HO et al. (1999 a, b) and STEGER (2006). At all of these field tests the increase in temperature played an important role for a successful chlorinated hydrocarbon removal.

Mathematical models can be very helpful to understand the different physical and chemical processes occurring during electroremediation. Additionally electroremediation models are essential to give a remediation forecast especially in field scale.

The numerical model presented here describes the coupled transport of charge and mass as well as the chemical speciation of a multicomponent system subject to an applied electric field. The major transport mechanism electroosmosis and electromigration, as well as pressure-driven convection and diffusion, are included. The model can also describe chemical reactions occurring in the bulk liquid, interactions in the soil such as heterogeneous reactions, sorption processes and electrochemical reactions occurring at the electrodes. This classical numerical is advanced by the implementation of the calculation of the temperature distribution. The estimation and accurate computation of the heat source is problematic, because depending on the strength of applied energy heating effects or kinematic processes (electromigration and electrosmosis) are dominating (figure1).

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Figure 1: dominating mechanism in dependency on the applied energy (after PAMUKCU 2005).

Beside other physicochemical effects like electrode reactions the model has to be to extend to unsaturated soil conditions, especially in the presence of volatile organic substances, because then diffusion processes can dominate pollutant transport in the gaseous phase especially at relatively high temperatures.

Finally numerical simulations of temperature effects occurring during applying a dc electric field are compared to laboratory and field scale experiments in different soils.

[1] Mitchell, J.K. (1993): Fundamentals of Soil Behavior, 437 S.; New York (Wiley &

Sons). [2] HO, S.V., ATHMER, C., SHERIDAN, P.W., HUGHES, B.M., ORTH, R., MCKENZIE, D.,

BRODSKY, P.H., SHAPIRO, A., THORNTON, R., SALVO, J., SCHULTZ, D., LANDIS, R., GRIFFFITH, R. & SHOEMAKER, S. (1999a): The Lasagna Technology for In Situ soil remediation. 1. Small field test. – Environ. Sci. Technol., 33(7): 1086-1091.

[3] HO, S.V., ATHMER, C., SHERIDAN, P.W., HUGHES, B.M., ORTH, R., MCKENZIE, D., BRODSKY, P.H., SHAPIRO, A., SIVAVEC, T.M., SALVO, J., SCHULTZ, D., LANDIS, R., GRIFFITH, R. & SHOEMAKER, S. (1999b): The Lasagna Technology for In Situ soil remediation. 2. Large field test. – Environ. Sci. Technol., 33(7): 1092-1099.

[4] STEGER, H. (2006): Elektrokinetische In-situ-Sanierung LCKW-kontaminierter gering durchlässiger Lockergesteine.- XXXIV-196 S., http://www.ubka.uni-karlsruhe.de/eva/index.html, Karlsruhe (Elektronisches Vollarchiv Eva) [Dissertation].

[4] PAMUKCU, S. (2005): Electrically Enhanced Transformation of Contaminants in Clay Rich Subsurface. – Presentation at the EREM Conference May 2005, Ferrara, Italy.

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http://www.ubka.uni-karlsruhe.de/eva/index.html



STRENGTHENING OF SOFT CLAY WITH ELECTROKINETIC STABILIZATION METHOD

Dilek Turera, Ayten Gencb

aHacettepe University, Department of Geological Engineering, Beytepe Campus, 06532, Ankara/TURKEY; bZonguldak Karaelmas University, Department of Environmental Engineering, Zonguldak/TURKEY E-mail: [email protected] Introduction: Electrokinetic remediation is a very effective method for clean up of heavy metal and organic pollutants from clayey soils. In this method, direct current by which dissolved charged ions are transported due to electromigration is applied between the electrodes. At the same time because of the negative surface of the soil, pore water moves toward cathode as a result of the electric field. The same method has been also tried for stabilization of soft clays by some researchers with the addition of stabilizing agents [1; 2]. In this application, soil strength is achieved by three mechanisms: cation replacement, mineralization and precipitation of species in pore fluid [3]. The problem with this application is that the improvement in the soil strength is observed only in limited area close cathode.

Method:

The electrokinetic unit, which is used in this study, was successfully used for cleaning of heavy metals from a clayey soil in a previous study [4]. The electrokinetic unit opposite to general trend of one anode electrode and one cathode electrode composed of multiple arrangements of electrodes. It consists of one anode and 8 cathode electrodes distributed in a circular manner. With this multiple arrangement of the electrodes the area affected with alkaline conditions is tried to be increased.

10 cm

5 cm10 cm 10 cm 5 cm5 cm

Power Source

Cathode

AnodeSoil CaCl2

Water

10 cm

5 cm10 cm 10 cm 5 cm5 cm

Power Source

Cathode

AnodeSoil CaCl2

Water

Figure 1. Circular electrokinetic Unit (After Turer and Genc, 2005)

In the experiments, Ankara clay has been used. First, the liquid limit of the clay was determined and samples were prepared at liquid limit of 73%. After placing the clay in the electrokinetic unit the clay is compacted under 130 kg weights. When there was no more compaction (in the dial gage reading the change in elevation), the weight was lifted. Next, the anode and cathode chamber was filled with distilled water and left for sample to equilibrate in the unit. A day after, the water in the anode compartment was discharged and the compartment was filled with 1 M CaCL2. Constant electrical potential of 10 V was applied to the sample for 3 weeks. At the end of the experiment liquid in the anode and cathode compartments were discharged and shear strength of the sample was measured with a laboratory vane apparatus. Soil was sampled in a radial

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manner at 2.5 cm and 7.5 cm away from anode as it is seen in figure 2. A part of the soil sample was kept untouched for sampling a week after the completion of the experiment. During this period electrokinetic unit was kept in a humidity cabinet.

Testing points after the treatment

Testing points one week after the treatment

Soil

Anode chamber

Cathode chamber

Testing points after the treatment

Testing points one week after the treatment

Soil

Anode chamber

Cathode chamber

Figure 2. Location of sampling points

Results: The measurement obtained at 7.5 cm distance from the anode was showed that shear strength of the samples increased up to 168.3 kPa. The shear strength of the soils at 2.5 cm from the anode did not changed much and the measurements were in average 11 kPa (Figure 3 a). The increase in the strength of the soil at 7.5 cm from anode, relative to 2.5 cm from the anode in the same data set were 703%, 689%, 903% and 1244%. The shear strength measurements taken one week after the completion of the experiment were 182.8 kPa and 101.57 at 7.5 cm and 13.74 kPa and 13.74 kPa at 2.5 cm distance from anode (Figure 3 b).

a)

Figure 3. Shear strength measurements with the addition of 1 M CaCl2

Conclusion:

A circular electrokinetic unit with multiple anode arrangement was used to increase the shear strength of the artificially prepared soft soil sample. The aim of using circular eleckrokinetic unit was to increase the area of soil affected from alkaline conditions and decrease the area subjected to acidic conditions. Although with this electrokinetic unit high improvement in the shear strength of the soil was obtained at locations close to cathode the areas close to anode did not show improvement in strength.

[1] Ozkan S, Gale RJ and Seals RK (1999) “Electrokinetic stabilization of kaolinite by injection of Al and PO4

3- ions”, Ground Improv 3:135-144. [2] Alshawabkeh ANand Sheahan TC (2003) “Soft soil stabilization by ionic injection under electric fields”, Ground Improv 7:177-185. [3] Asavadorndeja P and Glawe U (2005) “Electrokinetic strengthening of soft clay using the anode depolarization method”, B. of Engineering Geology and the Environment [4] Turer D and Genc A (2005) “Assessing effect of electrode configuration on the efficiency of electrokinetic remediation by sequential extraction analysis”, J. of Hazardous Materials B119, 167-174.

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INDUCED ELECTRICAL GRADIENTS BY HYPERFILTRATION IN CLAYS

J.P. Gustav Locha and Katja Heisterb

a Department of Earth Sciences – Geochemistry, Faculty of Geosciences, Utrecht University, PO Box 80021, 3508 TA Utrecht, The Netherlands; E-mail: [email protected] b Lehrstuhl für Bodenkunde, Department für Ökologie- und Ökosystemmanagement, Wissenschaftszentrum Weihenstephan für Ernährung, Landnutzung und Umwelt, Technische Universität München, D-85350 Freising-Weihenstephan, Germany Introduction Hyperfiltration or salt sieving occurs when a salt solution is forced through a clay layer, e.g. in field aquitards and in clay membranes in technological applications. In the absence of electrical shorting, two types of electrical potential gradients can be induced during hyperfiltration through a clay membrane: Hydraulic flow induces a streaming potential gradient. The positive pole of this electrical gradient is at the downstream side of the membrane. The potential difference hampers the further downstream movement of ions, and therefore of water. Thus, the streaming potential causes an electroosmotic counterflow of solution. A membrane potential gradient develops when the membrane interfaces are in contact with solutions of different salt concentrations. The membrane potential gradient has its positive pole at the low-concentration (i.e. downstream) side of the membrane. Also this potential difference hinders the down-stream movement of ions, be it by convection or diffusion, and works as an electroosmotic counterflow of solution. Streaming potentials Streaming potentials across semi-permeable membranes are induced by water flow in response to hydraulic pressure gradients. Reported streaming potentials per bar in clays range from 0.12 to 180 mV·bar -1. Coefficients of electroosmotic conductivity (ke) range from 1·10-10 to 1·10-8 m2·V-1·s-1. Membrane potentials Membrane potentials arise due to a difference in salt concentration across a semi-permeable membrane. At perfect semi-permeability the potential difference is given by the Nernst-equation. The positive potential is at the low concentration side of the membrane. Clay membranes are not ideal and therefore the membrane potential difference is smaller than this maximum value. For bentonite, Heister et al. [1] measured membrane potential gradients between 3.9 and 5.8 V·m-1, which are smaller than predicted from the Nernst-equation by a factor 4.5-5.5. Hyperfiltration in bentonite clay Fritz and Whitworth [4] conducted a hyperfiltration experiment with a 0.01M LiCl-solution and a 3 mm thick membrane of Li-saturated bentonite of 90 % porosity. A fixed volume flux, Jv , of 1.37·10-5 cm·s-1 was applied. Thus, a hydraulic pressure difference of 20.47 bar developed across the membrane. At steady state they observed a peak concentration of 0.0348 M at the high-pressure interface of the clay membrane, which is ascribed to semi-permeability of the clay. The resulting osmotic pressure difference is calculated to be 1.215 bar.

85

Estimation of induced electroosmosis For estimation of the streaming potential gradient in the experiment by Fritz and Whitworth, the conditions of the experiments by Heister et al. [2] are the nearest comparable. To obtain insight in the possible range of induced gradients, we also consider data from others. From the applied hydraulic pressure of 20.47 bar, an induced electrical potential, ∆E, is estimated to be in the range of 0.123 V to 3.68 V. The electroosmotic counterflow (Je) is

xEkJ ee Δ

−Δ=

)( (3)

with x positive in the downstream direction. Using the corresponding ke-values reported by these authors, the electroosmotic counterflow (Je) of water is estimated in the range of -1.96·10-5 to -2.05·10-5 cm·s-1. The maximum value of the membrane potential gradient in the experiment is negligible in comparison with the streaming potential. Discussion The estimated streaming potential gradient during hyperfiltration creates a counterflow of water of the same order of magnitude as the fixed downstream flow. This counter-flow will not have affected the salt sieving observed. However, it will have affected the required pressure on the input solution. This must have been higher than in electrically shorted condition. In the presence of a counterflow Je , the volume flux, Jv , of the solution equals the sum of a hydraulic, a chemico-osmotic and an electroosmotic component. While ignoring induced electroosmosis , Fritz and Whitworth [4] estimated a membrane efficiency for chemico-osmosis, σ, of 0.55. A chemico-osmotic (counter)flux of -4.62·10-7 cm·s-1 is derived. Since salt sieving was observed, σ must be >0. However, as was found in earlier studies on bentonite (e.g. Keijzer and Loch [3]), the membrane efficiency probably is a factor 10 to 20 smaller. Although the estimated electroosmotic flux, Je, is is obviously too large, chemical osmosis in hyperfiltration may be small compared to induced electroosmosis. The excess hydraulic pressure characteristic for hyper-filtration may be mainly due to electroosmotic counterflow. Conclusions In clays where hyperfiltration is observed, be it in the field or in the laboratory, a streaming potential gradient and electro-osmotic counterflow may be present if the clay is not electrically shorted. This will result in a larger required hydraulic pressure. If these induced electrical effects are neglected, the role of chemical osmosis and the semi-permeability of the clay are overestimated. [1] Heister, K., P.J. Kleingeld and J.P.G. Loch. 2005b. J. Colloid and Interface Sci. 286: 294-302. [2] Heister, K., P.J. Kleingeld, T.J.S. Keijzer and J.P.G. Loch. 2005a. Engineering Geology 77: 295-303. [3] Keijzer, Th.J.S. and J.P.G. Loch. 2001. Soil. Sci. Soc. Am. J. 65: 1045-1055. [4] Fritz, F.J. and T.M. Whitworth. 1994. Water Resources Research 30: 225-235.

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Electrokinetic and Electrochemical Degradation


ELECTROCHEMICAL TREATMENT OF PHARMACEUTICAL WASTEWATER BY COMBINING ELECTROCHEMICAL

OXIDATION WITH OZONATION Menapace, Hannesa; Díaz, Nicolásb

a Institute for Sustainable Waste Management and Technology - University of Leoben, Peter-Tunner-Strasse 15 - 8700 Leoben, Austria; bChemical Engineering Department, University of Concepcion, PO Box 53-C, Correo 3, Concepcion, Chile. E-mail: [email protected] Introduction The topic of this research project, started in December 2006, is to eliminate pharmaceutical substances and complexing agents found in waste water as micropollutants. Although pharmaceuticals are absorbed by human and animal organisms after their intake, significant amounts of the active substances are excreted without alteration. Several scientific reports have been published about the pollution of surface- and groundwater with pharmaceutical substances. The objectives of the current project focus on an electrochemical treatment of pharmaceutical wastewater by combining two different techniques: electrochemical oxidation and ozonation. Although these impurities are at very low concentrations (in the scale of ng/L up to µg/L), scientists have not been able yet to estimate all involved possible risks, its investigation will be forced in the future. As an example, the release of pharmaceuticals to nature via wastewater could lead to an increased dissemination of antibiotic resistance. Endocrine substances like hormones are suspected to promote feminising and masculinising effects on organisms in ecosystems.

The aim of the current project is to achieve the most complete elimination of the examined substances with the combination of electrochemical oxidation and ozonation. For the development of the treatment process (Figure 1) a total running time of 2.5 years is scheduled.

Figure 1: Scheme of the planned workflow

Process combination The complete treatment would be done in two steps. In the first one, the wastewater will be treated by electrochemical oxidation with diamond electrodes. Then ozonation completes the process. The ozone will not be produced as the conventional ozone

89

producing systems; i.e., with coaxial dielectric-barrier-discharge in air. In this case ozone will be formed by electrolysis with diamond electrodes.

The whole process can be described as follows. Firstly, the wastewater under analysis will be taken from the effluent of a wastewater treatment plant (RHV-Leoben) and will be treated in a lab scale unit. In the second phase – after approximately one year – water from the local hospital in Leoben and a circuit board producer will be sampled. This wastewater will be treated on the pilot plant. Additionally, experiments will be carried on directly at the wastewater treatment plant. To accomplish this, a tech scale unit will be installed in a bypass-system of the facility.

The needed amount of ozone will be produced in a non-conventional, separate generator. In this process the ozone will be directly produced from clean water by electrolysis with diamond electrodes. The injection of the concentrated ozonic water to the wastewater will be progressive. After ozone addition, a post mixing chamber for the mixture will be used to install a sensor at this step. With this ozone detector, it will be possible to calculate an ozone balance of the reactor system. This balance in addition to the other parameters (e.g. COD, Chemical Oxygen Demand and DOC, Dissolved Organic Carbon) will allow getting conclusions about the ozone consumption of the substances existing in the sample, which depends on the existing organic matrix of the water samples (scavengers).

In the second treatment step, the waste water will be delivered to an electrochemical reactor. Inside, electrodes for an anodic oxidation with doped diamond electrodes are located. In the process OH-radicals will be directly produced and used for the oxidation of the substances (pharmaceuticals and complexing agents).

Analysis As shown in Table 1, the samples taken after the treatment modules will be analysed for several different parameters (e.g. DOC, COD, AOX, conductivity, redox potential, pharmaceutical substances and complexing agents content). The pharmaceutical substances and also the complexing agents will be analyzed by the Federal Environment Agency of Austria (this agency has been a project partner in different studies about pharmaceuticals in the ecosystem, as in the ARCEM project). COD and DOC will be analysed by the laboratory of the Institute for Sustainable Waste Management and Technology in Leoben, and the other parameters will be measured using inline instruments during the test runs.

Table 1: Overview of the analytic plan

IAE UBADOC XAOX XConductivity XRedoxpotential XpH-Value XCOD XCarbamazepin XCoffein XRoxithromycin XErythromycin-H2O XJosamycin XDiazepam XTrimethoprim XSulfamethoxazol XEDTA XDTPA X1,3-PDTA XNTA X

pharmaceuticals

complexing agents

sum parameter / online measurement

made byAnalysisSubstances

90


SOIL REMEDIATION BY ELECTRO SYNTHESIS OF OXIDANTS AND THEIR ELECTROKINETIC DISTRIBUTION

Heidi Mikkolaa, Wolfgang Wesnerb, Julia Schmalea, Slagjana Petkovskaa

aInstitute of Sustainable Waste Management and Technology; University of Leoben, Peter-Tunnerstrasse 15, 8700 Leoben Austria; bEchem, Viktor-Kaplan-Straße 2, 2700 Wr. Neustadt, Austria E-mail: [email protected] Introduction A new method for electrokinetic soil remediation for in-situ treatment is being developed. The technique combines anodic production of oxidizing agents with their electrokinetic distribution and is applied to the remediation of soils contaminated with organic pollutants. In this study, boron doped diamond (BDD)-anodes are used for the production of oxidants. The advantage of BDD-anodes is their high overvoltage enabling the production of powerful oxidizing agents from the electrolyte. As sulphate containing electrolytes are used, it can be assumed, that among others hydroxyl radicals (OH•) and peroxodisulphates (S2O8

2-) are produced. These ions are transported in an electrochemical field generated in the soil, where the chemical decomposition of contaminants takes place. The transport of oxidizing agents in soil occurs via electroosmosis and electromigration. In order to investigate the principles and limitations of the new technology, different kinds of preliminary tests were required. Among others, the formation and the transport of oxidizing agents were studied. Production of oxidizing agents The most crucial prerequisite for a successful remediation process is to produce enough water soluble oxidizing agents. Therefore, the electro synthesis of peroxodisulphate was conducted with a bipolar flow cell of several boron-doped diamond electrodes. The experiments were carried out testing a number of parameters such as current density (22, 44, 67 mA/cm2), electrolyte (Na2SO4 with different concentrations of H2SO4) and temperature (20, 30, 40°C). Samples were taken from the electrolyte and analyzed for oxidants by iodometric titration. According to the results the highest amount of oxidizing agents was produced at 67 mA/cm2. The production rate remained constant between 20 and 35°C, but decreased as the temperature rose over 40°C. The pH of the electrolyte did not have any influence on the production efficiency. Transport of oxidizing agents Different methods were tested in order to investigate transport velocities of oxidizing agents in electric fields in soils. The experiments were conducted both in aqueous and solid media. For the solid phase, the tests were run in vertical and horizontal directions. The best experimental set up proved to be a vertical arranged system consisting of two cylindrical reactors, an electrolyte cell and two electrodes (see Figure 1). The cylinders were filled with soil material, which had earlier been mixed with starch and potassium iodide solution. The cylinders were placed into an electrolyte solution. In order to separate the synthetic soil from the electrolyte, membranes were attached to the bottom of the tubes. Round electrodes were placed on the top of each cylinder to generate an electrical field through the system. Due to electromigration, the oxidizing agents are transported towards the anode while electroosmosis drives water towards the cathode. The ion movement can be observed through a color change in the soil, caused by the oxidation of I- to I2 in the presence of starch. As the oxidants’ transport occurs vertically against the gravity force, its influence on the transport can be ignored. This set up makes it possible to investigate

91

separately the ion transport caused by electromigration (right cylinder in Fig.1) and by electroosmosis (left cylinder in Fig. 1). Transport caused by capillary force and diffusion takes place in both cylinders.

Transportvelocity of S2O8

2--ions in sand

0

0,5

1

1,5

2

2,5

3

0 1 2 3 4 5

Field voltage [V/cm]Tr

ansp

ort [

cm/h

]

Figure 1. Experiment set up. Figure 2. Transport velocity with different field voltages.

The influence of field voltage on the transport velocity in sandy soil was investigated by using 1, 1,5, 2 and 4 V/cm. The transport kinetics speeded up linearly with the increasing field voltage (see Figure 2). Also the effect of different soil materials on the transport was tested. Mixtures of pure sand, loam and clay were prepared and the transport in these soils tested. According to the results, electromigration towards the anode was fastest in sandy and loamy soil, whereas transport occurred also in cathode direction in loamy soil. Latter can be explained by electroosmosis. The results of these experiments are presented in Table 1.

Table 1. Transport velocities of S2O82- ions in different soil types with 1 V/cm.

Transport velocity Sand Loam (Sialin) Clay

(Kaolin) Towards Anode [cm/h] Towards Cathode [cm/h]

100 % 2 0 100% 3,3 1,3 100% 0 0,7

50 % 50 % 2,4 0,9 50 % 50 % 0 0

50 % 50 % 0 0,6 33 % 33 % 33 % 2,1 0

Conclusions The anodic production of oxidizing agents, as well as the transport of these ions in soil has been investigated. The production process has been optimized and needs to be verified in a scaled up system. The results of the transport experiments indicate the importance of laboratory scale tests with existing soil material (from real site) before applying an electrokinetic remediation method in the field.

92


ON SITE AND IN SITU PRODUCTION OF OXIDANTS FOR SOIL REMEDIATION

W. Wesner*a, A. Diamanta, B. Schrammela, M. Unterbergera, H. Mikkolab

aEchem, Kompetenzzentrum für Angewandte Elektrochemie, Viktor Kaplan Str. 2 2700 Wiener Neustadt, Austria bIAE, Univ. Leoben Peter Tunnerstrasse 15 8700 Leoben Contact: [email protected] In Anodic oxidation processes the composition of the electrolyte is, besides the type of electrode employed, the most important factor defining kind and quantity of the produced oxidants. Using clean water the production of oxygen, hydrogenperoxide and ozone, dependent on the applied current density, is possible. In presence of chlorides, chlorine is additionally formed. This is not accepted in many applications because of the secondary reaction of chlorine with organic substances which leads to AOX. As the production of chlorine is a function of the chloride concentration and the concentration of other oxidable substrate at the anode in many cases the reaction can be held at a low production rate by designing the composition of the treated solution. In defined reactions it is possible to generate also clorinedioxide, which is much more stable and therefore more suitable to be transported in soil. At presence of sulphates, peroxodisulphate is produced – one of the most powerful oxidants for soil remediation; especially in combination with iron- ions in the soil highly active OH radicals will be formed in situ. Using carbonates and hydrogencarbonates, percarbonates well known in washing powders will be supplied. For special applications manganese, peroxodiphosphates, complex iron and silver can transfer oxidant- equivalents with high potentials to contaminations in the soil. Organic substances can be directly oxidised at electrodes with a high overpotential for the evolution of oxygen. Dependent on the mixture of oxidisable molecules in the solution, electrodes using directly the solution of the soil produce different compositions of oxidants. The composition of these oxidants can be approximated by modelling based on the substance specific production rates of the single reactions. The rate of direct destruction of organic substances at the anode can also be shown to be dependent on the concentration of oxidants at the electrode and dependent on the temperature at the surface of the electrode. In order to optimise the reactions for an economic on site production of oxidants one way is to create highly concentrated solutions of pure substrates. The alternative way is to mix different oxidant forming agents, optimising the over all production of oxidation equivalents. A number of mixtures containing sulphates, carbonates and other ions have been tested successfully, giving higher yields than concentrated solutions of single components. Different electrodes have been tested applying variable current densities. The influence of the final composition of oxidants in mixtures of inorganic salts could be shown. While classical dimension stabile anodes (DSA) based on titanummixedoxide show higher chlorine and oxygen production in various chloride containing electrolytes. All kind of boron doped electrodes oxidise preferably sulphate and water for persulphate and hydrogenperoxide, at higher current densities ozone. The best results were obtained using bipolar diamond electrodes made of single boron doped diamonds fixed in a fluorinated polymer. This cell also showed the highest durability and lowest cost of all diamond electrodes available on the market. As there is a bipolar arrangement

93

necessary, it is not useful to operate these electrodes in situ, but on site. A possible application is in a circular pump and treat remediation, where soil water is pumped trough the cell and released to the soil again. Enriching the solution with ecological compatible inorganic salts (e.g. carbonates, sulphates, nitrates) can help to improve the application. High yields oxidants can be produced this way. Compared with direct production in the soil the lower energy consumption and the high durability of the on site system is of interest for oxidative remediation processes. A demonstration cell will be shown at Vigo.

Reference

C. Comninellis et al. 2005. Application of Synthethic Boron-Doped Diamond Electrodes in Electrooxidation Processes. In: A. Fujishima, Y. Einaga, T. N. Rao, D.A. Tryk; 2005 Diamond Electrochemistry. Amsterdam: Elsevier, pp. 449 ff

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Posters

6th Symposium on Electrokinetic Remediation Poster 01 EREM 2007

ELECTROKINETIC DEWATERING AND REMEDIATION OF RIVER DREDGED CONTAMINATED HIGH WATER SEDIMENTS

Ha Ik Chunga, Jun Yub

a Research Fellow, Korea Institute of Construction Technology, 2311 Daewha-dong Ilsan-gu Goyang-shi Gyeonggi-do, Korea, Tel +82-31-910-0216, Fax +82-31-910-0211 E-mail: [email protected] b Senior Researcher, Korea Institute of Construction Technology, 2311 Daewha-dong Ilsan-gu Goyang-shi Gyeonggi-do, Korea E-mail: [email protected] Generally, the sediments contain significant water, clay, colloidal fraction and contaminants, and can results in soft strata with high initial void, and its potential hazards in subsurface environments are existed. Electrokinetic technique has been used in dewater process for volume reduction of high water content sediments and in remediation process for extraction of contaminants from contaminated soils. In this research, the coupled effects of dewatering and remediation of contaminated high water content sediments are focused using electrokinetic dewatering and remediation techniques from experimental aspects. A series of laboratory experiments including variable conditions such as water content of sediment specimen, solid content of sediment specimen, concentration level of the contaminant, and magnitude of applied voltage are performed with the contaminated high water sediment specimens sampled from river environment. From the test results, a significant investigation is derived for the mechanisms associated with sediments contaminated with hazardous substance in which simultaneous dewatering and remediation processes are involved by electrokinetic dewatering and remediation system. The coupled effects of dewatering and remediation of slurry type sediment are analysed. The test results show that the dewatering and settlement of specimen is increased with increasing of applied voltage and decreasing of solid content by the process of electrokinetic dewatering mechanism. And the concentration of sediment specimen is decreased with increasing of applied voltage and operating duration by the process of electrokinetic remediation. The contaminated high water sediment can be effectively dewatered and remediated by the coupled effects of electrokinetic dewatering process and remediation process.

Saturatedslurry

sample(+)

Powersupply

Electrode

Electrode

Filter

Powersupply

Electrode

Electrode

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Saturatedslurry

sample(+)

Saturatedslurrysample

(+)

Fig. 1 EK test layout

97

10.0

11.0

12.0

13.0

14.0

15.0

16.0

0.0 20.0 40.0 60.0 80.0 100.0

° æ° ú½ Ã° £, hr

°è¸é°í, c

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° æ° ú½ Ã° £, hr

Àü·ù, mA

ek1

ek2

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[1] Ha Ik Chung, etc., “Electrokinetic Sedimentation and Remediation of River Dredged Contaminated Soil, Spring Conference of Korea Geotechnical Society, 2001.3

98


ELECTROKINETIC ULTRASONIC REMEDIATION OF CONTAMINATED ADMIXED SOILS WITH VARIOUS CLAY AND

SAND CONTENTS Ha Ik Chunga, Masashi Kamonb

a Research Fellow, Korea Institute of Construction Technology, 2311 Daewha-dong Ilsan-gu Goyang-shi Gyeonggi-do, Korea, Tel +82-31-910-0216, Fax +82-31-910-0211 E-mail: [email protected] b Professor, Kyoto University, Japan

Various remediation techniques such as simple soil flushing, electrokinetic flushing,

ultrasonic flushing, and electrokinetic + ultrasonic flushing remediation were studied for the removal of heavy metal and organic substance in contaminated clayey soils. The study emphasized the coupled effects of electrokinetic and ultrasonic flushing techniques on migration as well as clean-up of contaminants in clayey soils. The laboratory soil flushing tests combined electrokinetic and ultrasonic technique were conducted using specially designed and fabricated devices to determine the effect of these both techniques. The electrokinetic technique is effective in removal of heavy metal in contaminated cohesive fine soil and the ultrasonic technique is effective in removal of organic substance in contaminated cohesionless granular soil. The removal of heavy metal and organic substance can be achieved by the coupled technique with electrokinetic and ultrasonic remediation.

A series of laboratory experiments involving the simple soil flushing, electrokinetic flushing, ultrasonic flushing, and electrokinetic + ultrasonic flushing test for clayey soil were carried out. An admixed soil with sand and clay was used as a test specimen, and lead and phenanthrene were used as contaminants of heavy metal and organic substance. In electrokinetic and ultrasonic flushing tests, an increase in out flow, permeability and contaminant removal rate was observed. Some practical implications of these results are suggested in terms of technical feasibility of in situ implementation of the coupled electrokinetic and ultrasonic remediation technique in clayey soil. An admixed soil in the ratio of sand and clay was used as sandy clay mixtures. The mixing weight ratios of sand and clay were 50 : 50, 20 : 80, 0 : 100 as a percentage, respectively. Test results are shown in the following figures.

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Figure 1. Accumulated outflow volume with 12 test cases

99

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Norm alized distance from anode (x/L)

Concentration ratio (C/Co)

S(S20 C80) E(S20 C80)

U(S20 C80) E+U(S20 C80)

Figure 2. Normalized concentration of lead for mixed soil with sand 20% and clay

80%

0.00.10.20.30.40.50.60.70.80.91.0

S50 C50 S20 C80 C100

Mea

n co

ncen

tratio

n ra

tio (C

/Co

S E U S E U S E U

Figure 3. Mean concentration of lead in specimen for clayey soil

0.00.10.20.30.40.50.60.70.80.91.0

S50 C50 S20 C80 C100

Mea

n co

ncen

tratio

n ra

tio (C

/Co

S E U S E U S E U

Figure 4. Mean concentration of phenanthrene in specimen for clayey soil

---------------------------------------------------------------------------------------------------------- [1] Ha Ik Chung, Masashi Kamon, “Ultrasonically enhanced electrokinetic remediation for removal of Pb and phenanthrene in contaminated soils’, Engineering Geology 77 233-242, 2005.

100


THE USE OF AN AIRLIFT REACTOR WITH IN-SITU ELECTROGENERATION OF FENTON´S REAGENT IN THE

TREAMENT OF SPENT CAUSTIC FROM A PETROLEUM REFINERY

Patricio Nuñez, Henrik K. Hansen, Jaime Guzman Universidad Técnica Federico Santa María, Av. España 1680, Valparaiso, Chile E-mail: [email protected] An airlift reactor was used to study the kinetics of the COD (chemical oxygen demand) reduction, where the Fenton´s reactive is generated in situ, using the inlet of air as a source for oxygen supply and agitation. This reactor was used to study the kinetics of spent caustic from a petroleum refinery. Spent caustic is generated as a results of the removal of sulphurs and mercaptans in petroleum refineries. Spent caustic is considered to be a hazardous waste. The main hazardous characteristics of this waste are the high COD (Chemical Oxygen Demand) and the high amount of sulfides. Normally the WAO (Wet Air Oxidation) technology, which uses oxygen to oxidize the Spent Caustic at high temperatures (between 200 and 280[°C]) and high pressures (up to 150[bar]), is used. This treatment is expensive and due to operating conditions generates a potential hazard situation [1]. New results show that Fenton´s reagent (Fe2+ + H2O2) is suitable as on oxidizing agent [2]. In order to reduce reagent addtion, an alternative treatment: a pH reduction followed by an Electro-Fenton process, is recommended for this waste. This reactor was set up as two iron concentric stell cylinders, which function as sacrificial anodes. The Fe2+ produced act as source for Fenton´s reagent together with added H2O2. An airflow passing between the plates induced the mixing of the two phases - without the need of a stirrer -, generating turbulent conditions. Initial results with electrocoagulation based on this type of reactor of arsenic were published earlier by the authors [3,4]. Figure 1 shows the actual reactor. a) b)

Figure 1. Airlift reactor for electrogeneration of Fenton´s reagent. a) side view, and b) top view.

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The volume of the reactor was 1,2 [L]. The spent caustic solutions were prepared with phenol (2.500 ppm) y sodium sulfhydrate (NaSH) (10.000 ppm). The Electro-Fenton process begins as mentioned with the production of the catalysator Fe+2, in concentration of about 100 mg/L, when connecting the electrodes to a power supply (with 1[A] current. The process continues with the addition of hydrogen peroxid (30 % w/w) in a estequimetric ratio with the initial COD present in the wastewater sample. The operational temperature was kept constant during 60 [min] of experimental running and samples were taken after 15, 30, 45 y 60 [min] for COD and phenol analysis. Results showed that more than 90 % COD reduction could be obtained using this reactor. A set of residence time distribution and kinetic experiments were run on pilot scale with an airlift reactor to determine a model for the hydrodynamic and the kinetic parameters. An overall kinetic model that lumps the different reactions for the real spent caustic and specific reaction model for Sulfide and phenol, were developed and the kinetics parameters were fitted using the fluidynamic model developed by the authors.

[1] Cordonnier, F.B.a.J., Refining, Petrochemicals and Gas Processing Techniques. INDUSTRIAL WATER TREATMENT. 1 ed. Vol. 1. 1995, Houston, Texas, USA: Gulf Publishing Company. 248. [2] A. Ventura, G. Jacquet, A. Bermond, V. Camel. Electrochemical generation of the Fenton’s reagent : application to atrazine degradation. Water Research, 36 (2002), 3517-3522. [3] Hansen, Nuñez and Grandon, Minerals Engineering 19 (2006) 521-524. [4] Hansen, Nuñez, Raboy, Schippacasse and Grandon, Electrochimica Acta 52 (2007) 3464-3470.

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ARSENIC REMOVAL FROM COPPER SMELTER WASTEWATER BY ELECTROCOAGULATION IN AN AIRLIFT REACTOR

Henrik K. Hansen, Patricio Nuñez, Sandra Aguirre, Alejandro Jeria, Cesar Jil. Departamento de Procesos Quimicos, Biotecnologicos y Ambientales, Universidad Tecnica Federico Santa Maria, Avenida España 1680 Valparaiso, Chile, e-mail: [email protected]

Copper smelters – and the sulfuric acid plants that are connected to them – generate large amount of wastewater containing heavy metals, where arsenic is the key contaminant. Heavy metals such as copper and lead can normally be removed by sulfide precipitation but arsenic needs other treatment. Electrocoagulation to precipitate the arsenic through the in-situ production of ferric hydroxide was tested in an air lift reactor. This reactor was set up as two iron concentric cylinders. An airflow passing between the plates induced the mixing of the two phases - without the need of a stirrer -, generating turbulent conditions. Initial results with elecoagulation of arsenic were published earlier by the authors [1,2]. A set of synthetic wastewaters was used to test the performance of the reactor. The initial concentration varied from 10 to 5000 ppm of arsenic. Continuos current with current reversal each 60 or 120 seconds in order to avoid the passivation of the electrodes was applied. The gap between the electrodes was 10 mm for the reactor, and the current density was varied between 0.8 – 3 mA/dm2 depending on experiment. The reactor was run in continuos and batch wise operation, and the elapsed time for each experiment was 120 to 180 minutes. The results from the batch experiments were used to predict the performance of the continuos experiments and vice versa as a validation procedure. The reactors are showed in Figure 1. The airlift reactor was applied to real wastewater sampled at the El Teniente copper smelter gas treatment plant. The arsenic content in the wastewater was found to be between 6 and 15000 ppm – depending on the sampling stage in the treatment plant. Both batch and continuous experiments were carried out. In general the arsenic removal was efficient – e.g. a batch reactor experiment run at 1.2 mA/dm2 and initially 100 ppm arsenic showed that a more than 99 % reduction in the arsenic concentration after 3 hours was possible. Initial results were published earlier by the authors [1,2]. Residence time distribution experiments were run on both types of reactors, and a model that takes in account a) the kinetics on the solid phase (electrochemical phenomena), b) the mass transfer process, c) the ferrous ion oxidation with the ferric hydroxide production, and d) residence time distribution models, was developed and the kinetic parameters were fitted.

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a) b)

Figure 1. Airlift reactors: a) batch and b) continuous reactor. A set of residence time distribution and kinetic experiments were run on pilot scale with an airlift reactor to determine a model for the hydrodynamic and the kinetic parameters. Based on these results a scale up procedure was developed to design an actual full scale electrocoagulation reactor. The reactor is compared process wise and cost wise with the conventional industrial reactor that use ferric sulfate addition the precipitate arsenic.

[1] Hansen, Nuñez and Grandon, Minerals Engineering 19 (2006) 521-524. [2] Hansen, Nuñez, Raboy, Schippacasse and Grandon, Electrochimica Acta 52 (2007) 3464-3470.

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INTEGRATED ELECTROKINETIC REMEDIATION TECHNOLOGIES: OPPORTUNITIES AND CHALLENGES

Krishna R. Reddy, Ph.D., P.E. Professor of Civil and Environmental Engineering, University of Illinois at Chicago, 842 West Taylor Street, Chicago, Illinois 60607, USA; E-mail: [email protected] Remediation of contaminated sites is a top priority of environmental professionals to protect public health and the environment. Unfortunately, many conventional in-situ remediation technologies are found to be ineffective and/or expensive to remediate sites with low permeability and heterogeneous subsurface conditions1. In-situ electrokinetic remediation is continuing to be extensively investigated for over a decade as a potential technology to remediate such difficult subsurface environments. The objectives of this paper are: (1) to present difficulties in implementing the standard electrokinetic remediation process; and (2) to outline the opportunities and challenges in developing and implementing promising integrated electrokinetic remediation technologies. Numerous bench-scale studies have been reported which use ideal soils such as kaolin spiked with a selected single contaminant (e.g., lead or phenanthrene) to understand the contaminant transport processes. However, only a limited number of studies have been reported on real-world soils contaminated with a wide range of aged contaminants, and these studies have been helpful in recognizing complex geochemical interactions under induced electric potential. All of the bench-scale studies have clearly documented that non-uniform pH conditions are induced by applying a low direct current or electric potential, complicating the electrokinetic remediation process. Low removal of contaminants was observed in these studies, and detailed geochemical assessments were made to understand hindering mechanisms leading to low contaminant removal. In low acid buffering soils, high pH conditions near the cathode cause adsorption and precipitation of cationic metal contaminants, whereas low pH conditions near the anode cause adsorption of anionic metal contaminants. In high acid buffering soils, high pH conditions prevail throughout the soil, causing cationic contaminants to precipitate without any migration and anionic contaminants to exist in soluble form and migrate towards the anode. Removal of organic contaminants is dependent on the electroosmotic flow which varies spatially under applied electric potential. Initially, flow occurs towards the cathode, but it gradually decreases as electric current decreases due to depletion of ions in pore-water. If the soil pH reduces to less than point of zero charge (PZC), electroosmotic flow direction can reverse and flow could cease. Depending on the ionic strength, the electroosmotic flow may increase towards the cathode or the anode. Several studies have investigated strategies to enhance the contaminant removal by using different electrode conditioning solutions, changing the magnitude and mode of electric potential application, or both. The electrode conditioning solutions aim to increase the solubility of the contaminants and/or increase electroosmotic flow. When dealing with metal contaminants (including radionuclides), organic acids (e.g., acetic acid) are introduced in the cathode to neutralize alkaline conditions, thereby preventing 1Sharma, H.D., and Reddy, K.R. (2004), Geoenvironmental Engineering: Site Remediation, Waste Containment, and Emerging Waste Management Technologies, John Wiley & Sons, Hoboken, New Jersey, USA, 992p.

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high pH conditions in the soil. This allows the cationic metal contaminants to be transported and removed at the cathode. Alkaline solutions are introduced in the anode to increase pH near the anode. This allows anionic contaminants to exist in soluble form and be transported and removed at the anode. Instead of using acids, complexing agents (e.g., EDTA) can be used in the cathode. When these agents enter the soil, they form negative metal complexes that can be transported and removed at the anode. When addressing organic contaminants (including energetic compounds), solubilizing agents such as surfactants, cosolvents and cyclodextrins are introduced in the anode. When transported into the soil by electroosmosis, these agents solubilize the contaminants. Alkaline solutions are also introduced to maintain soil pH greater than PZC to enhance electroosmotic flow. Mixed contaminants (combinations of cationic and anionic metals and organic contaminants) are commonly encountered at contaminated sites. In general, the presence of multiple contaminants is shown to retard the contaminant migration and removal. Synergistic effects of multiple contaminants should be assessed prior to the selection of an enhancement strategy. It is found that the removal of multiple contaminants in a single step-process is difficult. Therefore, sequential conditioning systems have been developed to enhance removal of mixture of cationic and anionic metal contaminants and/or a mixture of metal and organic contaminants. In addition to the use of electrode conditioning solutions, the magnitude and mode of electric potential application is altered. An increase in the magnitude of electric potential increases the electromigration rate and initial electroosmotic flow rate. Pulsed mode of electric potential application is found to increase the electroosmotic flow due to polarization of soil surfaces and it also allows rate-limited dissolution of contaminants to occur. Although excellent removal efficiencies can be achieved by the use of different enhanced electrokinetic remediation strategies, several practical problems arise in using them at actual field sites. These problems include: high cost of electrode conditioning solutions, regulatory concerns over injecting conditioning solutions into subsurface, high energy requirements and costs, longer treatment time, potential adverse effects on soil fertility, and costs for treatment of effluents collected at the electrodes. As a result of all these problems, the full-scale field applications of electrokinetic remediation are very limited. Despite the challenges, in-situ electrokinetic remediation holds promise to remediate difficult subsurface conditions, particularly low permeability and heterogeneous subsurface environments, where most of other conventional technologies fail. The electrokinetic remediation technology can also be applied to remediate diverse and mixed contaminants even when they are non-uniformly distributed in the subsurface. Standard electrokinetic remediation method is essentially an electrokinetically enhanced flushing process. However, the electrokinetic remediation can be made efficient and practical as well as less expensive by integrating or coupling it with other proven remediation technologies. Such integrated technologies include electrokinetic-chemical oxidation/reduction, electrokinetic-bioremediation, electrokinetic-phytoremediation, electrokinetic-thermal desorption, electrokinetic- permeable reactive barriers, electrokinetic-stabilization, electrokinetic-barriers (fences), and others. These integrated technologies have potential for the simultaneous remediation of mixed contaminants in any subsurface environment. Several successful bench-scale and demonstration projects have been reported recently on integrated electrokinetic remediation technologies; such integrated electrokinetic projects are expected to grow in the near future.

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ELECTROKINETIC NUTRIENT TRANSPORT TO STIMULATE MICROBIAL CONTAMINANT DEGRADATION IN SANDY SOILS

Lohner S.T., Katzoreck D., Augenstein T., Schell H., Tiehm A.*

aWater Technology Center, Department Environmental Biotechnology, Karlsruher Straße 84, 76139 Karlsruhe, Germany *Corresponding author: E-mail: [email protected] phone: +49(0)721-9678220 fax: +49(0)721-9678101 Bioremediation, i.e. microbial degradation of toxic and xenobiotic compounds is a widely used and effective in-situ remediation strategy for organic groundwater contaminations. However, a pre-requisite for microbial degradation of groundwater contaminants is a sufficient bioavailability of all involved components. Often the availability of nutrients and electron acceptors is the limiting factor for successful bioremediation in the field. For ex-situ remediation technologies this limitation can be overcome by mechanical mixing. Under in-situ conditions, a heterogenous spatial distribution of microorganisms, contaminants, nutrients, and electron acceptors is observed and a mechanical mixing is not possible. In the aquifer, dispersion and mixing of components is determined by the predominant transport processes. These include convection, diffusion and dispersion. Transport of substances by convection can only occur in flow direction, a very limited mixing is occuring by dispersion and diffusion. In a plume of contaminated groundwater, microbial consumption of nutrients and electron acceptors results in small areas depleted in these components adjacent to areas where a low number of microorganisms is limiting biodegradation. Thus the relevant zone of mixing is in the pore-scale on which single microorganisms act. The objective of our study is to overcome these limitations by increasing the mixing in the contaminated aquifer. Electrokinetic processes are studied in order to improve mass transfer processes in the subsurface. First experiments focussed on the electrokinetic electron acceptor and nutrient transport in sandy soils. In laboratory scale columns, the electrokinetic transport of sulphate, phosphate, nitrate and ammonia was investigated as function of applied voltage gradient. Quartz sand was filled into a 10 cm long glass column. Deionized water was used as electrolyte. The electrolytes were circulated from a 1L-bottle into the electrode chambers. The relevant ion was introduced into the system at the corresponding electrode chamber (fig 1). Constant voltage of 10V and 20V was applied for electrokinetic ion transport. Break through of the components was investigated by regular measurement of ion concentrations in the anolyte and catholyte. Also the conductivity, pH and voltage were monitored throughout the experiment. The experiment was stopped when a constant transport rate of the ion was achieved and samples were taken from different soil segments and analysed for pH and nutrient concentration.

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It could be shown that the breakthrough of sulphate, nitrate and ammonium in the 10 cm sandy soil system was within several hours. Transport rates of app. 1.8 cm/h and 1.5 cm/h were observed for sulphate and nitrate at a voltage gradient of 2 V/cm. Decrease of the voltage to 1 V/cm resulted in a transport rate of about 0.7 cm/h for both ions. Ammonia had a slower transport velocity of about 0.5 cm/h at 2 V/cm and 0.2 cm/h at 1 V/cm, respectively. Migration of phosphate was low because it precipitated in the soil. Using of polyphophates was more successful, however, only low transport rates (between 0.1 and 0.5 cm/h at 2 V/cm) were observed. As the experiments were conducted without pH control, a pH gradient developed as expected. Within several hours the initial pH of 7 dropped about 5 units at the anode and increased up to pH 12 at the cathode. At the end of the experiment a pH gradient in the soil from 12 at the cathode to 2 at the anode was observed. There was a significant difference in transport behaviour when multiple ions were injected compared to single ion transport. When sulphate, phosphate, nitrate and ammonia were added at the same time, the amount and velocity of anion transport decreased slightly whereas the amount and velocity of ammonia transport was significantly enhanced due to competitive transport reactions. These preliminary results demonstrate the feasibility of the concept of electrokinetic transport of microbial nutrients and electron acceptors in the subsurface. The electrokinetic distribution is a promising tool for an in-situ stimulation of microbial degradation which is limited by mass transfer processes. Acknowledgment: We gratefully acknowledge financial support by the Federal Ministry of Economics and Technology and the German Federation of Industrial Research Associations "Otto von Guericke" e.V. (AiF) (project no 15131 N). We thank Hagen Steger and Roman Zorn for providing the electrokinetic test chamber.

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A NEW ELECTRODE BACKFILL MATERIAL FOR ELECTROKINETIC SOIL REMEDIATION

Steger, H.a, Zorn, R.ba Department of Applied Geology, University Karlsruhe, Kaiserstrasse 11, D-76128 Karlsruhe, Germany; b European Institute of Energy Research, University Karlsruhe, Emmy-Noether-Strasse 4, D-76131 Karlsruhe, Germany E-mail: [email protected] Important for a successful field application of the electrokinetic soil remediation is the electric and electroosmotic connection between the electrodes and the soil. Normally the electrodes are installed in a vertical or horizontal borehole or in a shaft. In dependency of the contamination and the geological situation different filling concepts are possible. Ordinary the options are the use of cuttings, clay suspensions or special backfill materials. Especially in the case of sandy clays with a medium hydraulic permeability or alternating storage the filling concept must achieve several different criteria. These criteria are:

• high electric conductivity • high electroosmotic permeability (stable ke-value and zeta potential) • low hydraulic permeability • non-polluting • long-term stable (chemical, physical and thermal) • easy to handle • economical

The main part of electrode backfill materials are mostly clay minerals. Under the action of an electric field these clay minerals could change their properties. For example kaolinite has normally high electroosmotic permeability but under low pH-values near the anode the electroosmotic permeability can decrease significantly [1]. Another frequent clay mineral, the montmorillonite, is especially sensible for structure changing caused by discharge of ions from the diffuse double layer [2]. These and a lot of other reactions influencing the efficiency and stability of backfill material could take place during an electrokinetic remediation process.

Hence, a new electrode backfill material was developed, which consists of illite, kaolinite, calcite, quartz, cement and water. Optionally a liquefier could be used to stabilize the cement containing backfill material. The mixture can be varied in dependency of a given local situation. Furthermore, the amount of illite, kaolinite and calcite can be adapted to the conditions at the anodes and the cathodes.

Long-term electrokinetic bench scale tests [3] (runtime of about 140 days) with two different mixtures of the new developed backfill material (M1A, M1K) and a natural soil (LVL2) were carried out. The comparison of the electroosmotic permeability shows that at the beginning of the experiment the ke-values of the backfill materials were higher than the ke-value from the soil (fig. 1). During the test the ke-values became nearly the same magnitude. Furthermore, no significant chancing of the soil structure and alteration were observed after the experiments.

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and a natural soil (LVL2). [1] ACAR, Y. B., GALE, R. J., HAMED, J. & PUTNAM, G. (1990): Acid/Base distributions

in electrokinetic soil processing.- Transportation Research Record, 1288: 23-33. [2] STEGER, H. (2006): Elektrokinetische In-situ-Sanierung LCKW-kontaminierter

gering durchlässiger Lockergesteine.- XXXIV-196 S., http://www.ubka.uni-karlsruhe.de/eva/index.html, Karlsruhe (Elektronisches Vollarchiv Eva) [Dissertation].

[3] STEGER, H., ZORN, R., HAUS, R. & CZURDA, K. (2001): Removal of tetrachlorethylene from fine-graind soils by electrokinetic processes.- In: CZURDA, K., HAUS, R., KAPPELER, C. & ZORN, R. [Hrsg.]: Erem 2001 - 3rd Symposium and status report on electrokinetic remediation, 63: 25-1 – 25-14; Karlsruhe (Schriftenreihe Angewandte Geologie Karlsruhe).

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ELECTROLYTIC GENERATION OF AN ALKALINE BARRIER FOR IN-SITU DEGRADATION OF MUNITION CONSTITUENT

(RDX) CONTAMINATED GROUNDWATER David B. Genta, Akram Alshawabkehb, Jeffrey L. Davisa

aEnvironmental Laboratory, USACE Engineer Research and Development Center, 3909 Halls Ferry Road, Vicksburg, MS 39180 USA, bDept. of Civil and Environmental Engineering, 400 Snell Engineering Center, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA E-mail: [email protected] Introduction. The use, manufacturing, and storage of nitroaromatic and nitramine explosive compounds resulted in contamination of soil and groundwater. The U.S. EPA lists hexahydro,1-3-5-trinitro-1,3,5-triazine (RDX) under the Unregulated Contaminant Monitoring Regulation for Public in List 2. RDX groundwater contamination disrupts the use of military training areas and impacts local drinking water.

Methods and Materials. Sand packed columns in a horizontal flow arrangement were used in laboratory experiments to simulate an in-situ treatment barrier (Figure 1). The simulated barrier was designed as a hybrid treatment process for RDX contamination, initially via reductive transformation at the cathode followed by alkaline hydrolysis downstream of the cathode. Experiments included one-dimensional proof-of-concept (5 cm ID) and scale-up optimized (10-cm ID) columns. The distance between the electrodes for the 5-cm and 10-cm columns was 33-cm and 160-cm, respectively. A seepage velocity of 30.5 cm d-1 was used in all experiments. Mixed metal oxide coated titanium electrodes (anode and cathode) were installed in slotted PVC wells within the column to facilitate the destruction of RDX contaminated water by electrolysis at the cathode and by alkaline hydrolysis downstream of the cathode. Ports placed at 30.5-cm intervals along the column were used for pH and RDX sampling.

Results and Discussion. The high pH migrated through the column from cathode to anode in 30 days of treatment (Figure 2a). Over the range of inlet concentrations (500 to 2,500 μg/L) for the 5-cm columns, RDX removal was approximately 95% with 75% RDX destruction near the cathode, presumably by electrolysis and 13% RDX destruction downstream of the cathode by alkaline hydrolysis with electrode current densities of 6.2 to 12.3 A/m2. An alkaline hydrolysis first order rate coefficient (0.046 hr-1) was used to estimate the optimized scale-up column length (160-cm) required for complete destruction of RDX and its nitroso-substituted products. Effluent RDX concentrations from the 10-cm diameter scale up column (500 to 4,000 μg/L influent) were less than the 2 μg/L health advisory standard established by the US EPA (Figure 2 b). The alkaline hydrolysis first order reaction rate coefficient from the 10-cm diameter column was 0.054 h-1 with a half life of 13.1 h.

Conclusions. The RDX removal percentage for the last 32 days of operation of 10-cm diameter column was 99.995 percent with an electrode current density of 9.2 A/m2. Nitroso-substituted products (MNX, DNX, and TNX) were below detection limits in the column effluent. The effluent end products of RDX ring cleavage detected were formate, nitrite, and nitrate. The significance of this in-situ electrochemical barrier is that the contaminant can be removed from the groundwater without the addition of external chemical amendments and it can be applied below trenching depths. Electrodes placed at the leading edge of a groundwater plume can act as a barrier to RDX transport.

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Figure 1. Depiction of an electrochemical barrier: (a) in-situ application of direct current across cathodes and anodes, (b) placement of cathode wells upstream of anode wells, (c) RDX decomposition at cathode by direct electrolysis, (d) alkaline front migration downnstream of cathode toward the anode, and (e) anode oxidation of methanol, formate, and nitrite.

Figure 2. 10-cm ID column results vs. time (a) pH from ports along column (b) effluent RDX (µg/L)

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DRYING BRICK MASONRY BY ELECTROOSMOSIS – SMALL PILOT PLANT

Lisbeth M. Ottosen, Inge Rörig-Dalgård Department of Civil Engineering, Building 118, Technical University of Denmark, 2800 Lyngby, Denmark E-mail: [email protected] INTRODUCTION Rising dampness is a well known problem. Water is sucked up in to the building structure from the groundwater by capillary forces. In areas where the groundwater is located just underneath the building foundation and where the soil is fine-grained, moisture problems in the structure will often occur if no precautions have been taken. When the rising dampness reaches the building structure it will cause problems partly because of the water and partly due to the dissolved salts in the groundwater. Moisture problems are e.g. wood destruction by dry-rot, frost damage, increased energy consumption for heating and plaster peeling. Furthermore humans can develop allergy from mold and fungal spores. The dissolved salts may also cause decay of the masonry. The present investigation is focused on electro-osmotic transport of water within masonry with the purpose of lowering the water content. A previous investigation showed that electroosmotic transport of water can be obtained in single bricks (master thresis, I. Rörig-Dalgård) and in the present investigation a pilot test was conducted, where electrodes were placed on a wet masonry wall. LOCALITY AND ELECTRODES The locality for the pilot experiment was a brick masonry house in two floors. The house is unheated and built around 1950. The experiment was made in the lower floor on an internal wall. The experimental wall (11 cm in thickness) is an internal wall of the house separating a room in two parts.

Figure 1: Electrodes at masonry wall

Both yellow and red bricks were found in the wall and the original mortar was carbonate based (hydraulic or air lime). The wall was covered with plaster, but the unfastened plaster was removed before the pilot experiment. Drilling samples from both bricks and mortar were taken at different positions for measurement of water content and concentrations of NO3

- and Cl- It is important that H+ produced at the anode will not be transported into the masonry because acidic pore fluids can destroy the mortar. From electrokinetic soil remediation, it is known that an acidic front develops very slowly in calcareous soils and it was chosen to place iron electrodes (rebar) in clay with high carbonate content (17-18%).The clay had a water content of about 20%.

Figure 1 shows two electrodes placed at the experimental wall. As seen, they are placed at the same side of the wall to simulate a situation, where it is only possible to get to the wall at one side as e.g. in a basement. The electrodes were 130 cm long. Between the

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wall and the metallic electrodes was a clay layer of 1.5 – 2.0 cm thickness. To keep the metallic electrode in place it was covered with about 1 cm clay. The electrodes were covered by plastic to avoid drying of the clay due to evaporation. RESULTS AND DISCUSSION The water content was between 10% and 15% in the bricks and between 3% and 6% in the mortar and the masonry of the experimental wall must be considered very moist. The chloride and nitrate concentrations were low and thus the moisture in the wall is expected originate from rising dampness rather than of hygroscopic origin. During the experiment 40 mA was applied to the electrodes. A piece of fabric was placed under the cathode, and this fabric was wet after less than 1 hour of applied current. The voltage was 60V at the beginning but after 34 hours the voltage had already decreased to 22 V, showing the main problem of the setup – it was difficult to maintain good electric contact. The problematic point was the interface between clay and masonry. If a few water droplets were added here the voltage increased again. Never the less the experiment was continued all together for 1 month. During this period the current was sometimes turned off and few times cathode and anode were changed for 2 hours, both resulting in a lower resistance for a short period. After 30 days it was seen, that about 350 ml water were collected under the cathode (see Figure 2). Unfortunately it was not observed when this water started to be collected and if it continued to arrive. The clay of the cathode was very wet, but the clay at the anode was hard as cement and the experiment was stopped since only 16 V could be obtained when applying 40 mA. From each electrode 10 samples were taken for measurement of pH and water content. At the anode pH had not lowered (>7.8) and the clay buffered the acidic front effectively.

Figure 2: Water collected

under cathode

Water content of the clay at the anode was < 13%. Even under during this experiment, where the electrodes not allowed for good electric contact, electroosmosis was obtained and there is basis for further development of an electrokinetic method for drying brick masonry. However, there are still many questions to be answered and also development of proper electrodes is needed. An optimization of the placement of the electrodes must also be made. In the present work the electrodes were placed vertically and this does not hinder water in continuing entering the wall from the soil. It may be a possibility to place the electrodes horizontally and close to the floor and by this hinder the transport of water further than the anode (placed above the cathode). This work is on-going. In some situations it may be advantageous to combine electroosmotic dewatering with isolation of the masonry from rising dampness by inserting a damp proof course in order to prevent the masonry continuously in receiving new water. In cases where there is a problem with hygroscopic moisture in the masonry, a damp proof course cannot solve the problem alone and in such a situation a combination of damp proof course and an applied electric field could also be advantageous. ACKNOWLEDGEMENT BoligfondenKuben is acknowledged for financial support for this project.

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ELECTROKINETIC SETTLING & SEDIMENTATION BEHAVIOUR OF COHESIVE SOIL IN DILUTE SUSPENSION

MyungHo Leea, Dae-Ho Kimb, Soo Sam Kimc aBK Research Associate, Dept. of Civil & Environ. Eng., Hanyang Univ., South Korea E-mail: [email protected] bGraduate Student, Dept. of Civil & Environ. Eng., Hanyang Univ., South Korea cProfessor, Dept. of Civil & Environ. Eng., Hanyang Univ., South Korea

ABSTRACT

Since the industrial revolution onwards, world wide pollution of groundwater resources with toxic metals has been significant threat and damage to human health and environment. Industrial wastewaters were discharged with into rivers without proper treatments, and the pollutants accumulated in aquatic sediments. Contaminated dredged soils contain large quantities of water and hence dewatering is frequently necessary after dredging in order to enable remediation treatment. Thus, the need has grown for developing cost effective and efficient techniques for in-situ remediation of large volumes of contaminated soil. This paper demonstrates settling and further consolidation behaviour of dredged clayey soil under the effects of electrokinetics.

Keywords: clayey soil, electrokinetics, heavy metal, pH, sedimentation

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Fig. 2. Surface settlement vs. time: (a) case1 – gravitational settling [iwc*: 500%, es*: distilled water], case2 – electrokinetic settling [iwc: 500%, es: distilled water], case3 – gravitational settling [iwc: 500%, es: 0.02M NaCl]; (b) case4 – gravitational settling [iwc: 2000%, es: tap water], case5 – electrokinetic settling [iwc: 2000%, es: tap water], case6 – gravitational settling [iwc: 2000%, es: 700 mg/L Zn]


[2] Bowden, R. K. (1988), “Compression behaviour and shear strength characteristics of a natural silty clay sedimented in the laboratory”, D.Phil. Thesis, Oxford University

[3] Lee, M. (2000), “An experimental and analytical study of electrokinetic consolidation”, M.Sc. Thesis, Oxford University.

[4] McRoberts, E. C. and Nixon, J. F. (1976), “A theory of soil sedimentation”, Can. Geotech. J., Elsevier, 13(3), pp. 294-305.

[5] Mitchell, J. K. (1993), “Fundamentals of soil behaviour”, Wiley Inter. Science [6] US Environmental Protection Agency (1997), “The incidence and severity of

sediment contamination in surface waters of the United States”, National Sediment Quality Survey, Vol. 1, EPA 823-R-97-006, Office of Water, Washington, DC.

[7] Yeung, A. T. (1994), “Electrokinetic flow processes in porous media and their applications”, Advances in porous media, Elsevier, 2, pp. 309-395.

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CORROSION REMEDIATION USING CHLORIDE EXTRACTION CONCURRENT WITH ELECTROKINETIC POZZOLAN

DEPOSITION IN CONCRETE

Henry E. Cardenasa, Kunal Kupwade-Patilb

aTrenchless Technology Center, Departments of Mechanical and Nanosystems Engineering at Louisiana Tech University, 600 W. Arizona St., Ruston LA, 71272 USA; bDepartment of Mechanical Engineering at Louisiana Tech University, 600 W. Arizona St., Ruston LA, 71272 E-mail: [email protected] This work examined the impact on corrosion when 20-nm pozzolanic nanoparticles are

driven into the capillary pores of relatively immature concrete. Two types of treatment

circuits were used, one driving the particles throughout the concrete specimen and the

other driving particles directly to the steel reinforcement. The specimens were initially

exposed to saltwater followed by Electrochemical Chloride Extraction (ECE) and

Electrokinetic Nanoparticle (EN) treatment. Scanning Electron Microscopy (SEM)

revealed a more densified microstructure due to EN treatment. It was found that the

reinforcement targeted treatments performed better than the specimen wide treatments.

Following 36 days of saltwater re-exposure, the control specimens exhibited severe

corrosion as compared to the reinforcement targeted treatment cases. The treatments

reduced porosity by 10% and increased tensile strengths by 25 % while causing the

conversion of 8 % of the available calcium hydroxide to a variant of C-S-H.

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Poster 12 6th Symposium on Electrokinetic Remediation EREM 2007

ELECTROKINETIC TREATMENT FOR FREEZING AND THAWING DAMAGE REMEDIATION WITHIN LIMESTONE

Henry E. Cardenasa, Pradeep Paturib

aTrenchless Technology Center, Departments of Mechanical and Nanosystems Engineering at Louisiana Tech University, 600 W. Arizona St., Ruston LA, 71272 USA; bDepartment of Mechanical Engineering at Louisiana Tech University, 600 W. Arizona St., Ruston LA, 71272 E-mail: [email protected]

ABSTRACT

Advances in sustainability can be achieved by extending durability. Freeze and thaw

damage is a major source of degradation in limestone structures that causes cracking

and increased porosity. The increase in porosity tends to compromise durability further.

Organic sealants used to curb the moisture intrusion are associated with ground level

ozone production. In addition, the limited penetration of these compounds tends to

cause freeze and thaw damage to occur deeper within the wall. This study investigated

the application of reactive electrokinetic treatment to improve the strength and

durability of limestone. The reactants in this case were sodium silicate and calcium

hydroxide. Treatments were applied to vertical surfaces using novel re-circulating flow

electrodes. A given treatment was applied for 12 days, during which sodium silicate

was driven deeply into the limestone block from one electrode and calcium hydroxide

from the other. The reactants met inside the stone and formed pore-blocking phases that

increased the strength while reducing porosity. Freeze and thaw damage was induced

within specimens in accordance with ASTM D 5312. The treatments prevented

deterioration of porosity and strength. In other cases, the treatments appeared to reverse

the effects of freeze and thaw damage. Some treatments yielded strength increases of

100% and higher.

118


REMEDIATION OF OIL-POLLUTED SOILS BY THE ELECTROCHEMICAL LIXIVIATION

V. A. Korolev & O.V. Romanyukha Russia, Moscow, Geological Faculty of MSU named M.V. Lomonosov E-mail: [email protected]

Oil and petroleum products are the extended environmental contaminants. Falling into the natural ecosystems, petroleum hydrocarbons disrupt the ecological state of soil covers and deform the structure of biocenoses. Currently, finding a solution of decontamination of soil cover from oil and petroleum products is a high priority. To date, not exist in the world efficient methods to remove of oil contaminants from soils. Therefore the development of the effective technologies of removal of petroleum pollution from soils, especially in the massifs, becomes of ever of more urgent. The electrokinetic method is one of the methods used to clean up the oil-contaminated soil in-situ. The application of this method will allow reducing the risk of contaminant impact on human beings and environment. Its utilization together with other decontamination methods will be helpful in eliminating oil spills on soil and significantly improve its sanitary state.

Our previous researches have showed that electrokinetic method improves efficiency of soil decontamination from 20% to 70% [1-4]. And yet, our experiments demonstrated that electrokinetic decontamination of oily soils is not capable of cleaning the sample completely. Hence, the experimental design should be different to enhance decontamination efficiency, particularly, under the flow conditions.

In the paper report are represented the results of study the possibility of using the method of electrochemical leaching for removal of petroleum pollution from soils, and also factors, which influence on its efficiency. In order to explore capabilities of the method and potential of its further improvement, we are continuing studies on the issue. The influence of composition and concentration of the lixiviating solution was investigated.

The study was conducted with model soil samples of soddy-podzolic soil, using the oil from the Usinsks field as a contaminant. To prepare of model samples, oil was added to the water-saturated soil with initial moisture corresponding to the upper plastic limit. Oil was added in the amount required to achieve the water-to-oil ratio of 1:0,6.

The laboratory study of electrochemical lixiviation soil decontamination from oil was performed in electro-osmotic cells flow conditions. The tube with soil sample was fixed at both ends by electrode chambers filled with washing solution and with platinum electrodes arranged inside but not too close to the soil. In the flowing regime in proportion to electricalosmosis cleaning washing solution from the lateral camera (anolyte) enters the model of soil and gradually washes it. For achievement of this into the lateral camera, with the positively charged electrode brought the capillary from the reservoir with the wash liquid. From the electrode camera with the negatively charged electrode, into which entered the escaping from model filtrate catholyte, solution entered the capacity- accumulator. In the course of experiment the current was applied to the soil sample during 6 hours. Then the collected filtrate was analyzed, and the sample was cut lengthwise in sections with subsequent moisture, pH and residual oil content determination for each section.

For investigating the possibility of applying the electrochemical lixiviation of soils as the lixiviating extractant was adapted the solutions of alkali - NaOH, and salts NaCl. In this case the concentration of the lixiviating solution must be such that, from one side,

119

would occur the most complete removal of oil from the soil, and from other side, the concentration must not exceed the critical value, with which occurs the sharp compression of dual electrical layer. In our studies washing solutions had the following concentrations NaOH - of 0,01, 0,05, 0,1 and 0,25 N and NaCl of 0,01 N.

The study results indicated that the oil remaining in the soil samples after decontamination, as under typical no-flow conditions, is redistributed, reflecting decrease of its concentration from the anode towards the cathode.

The estimation of a total quantity of oil remote of the sample confirms the noted by us tendencies in the previously carried out experiments under the non-flow conditions, that with an increase in the concentration of the washing solution NaOH occurs an increase in the effectiveness in the electrokinetic cleaning up to concentration NaOH of corresponding 0,1 N, with further increase in the concentration the effectiveness of cleaning is reduced.

Data analysis shows that the method of removal without the washing is considerably more effective in comparison with those previously examined by electrokinetic.

The conducted investigations made it possible to establish that the maximum effect of the removal of hydrocarbons from the sod-podzolic soil is achieved at concentration NaOH of 0,25 N and 0,1 N, and composes 81 and 93% respectively, while in the usual (non-lixiviation) regime with the same conditions the degree of cleaning it composed 70% and 82%. In this case in proportion to reduction in the concentration of alkaline washing solution to 0,01 N and 0,05 N the degree of cleaning is reduced and composes 70% and 79% respectively. In the experiments with neutral solution NaCl the degree of cleaning composed only 63%. Partial solubility of oil in alkali possibly promotes more efficient oil removal from the sample containing NaOH. Apparently, a part of hydrocarbon contaminant dissolves due to the electrokinetic inter-reaction with the alkali solution. The dissolution contributes to oil transfer from emulsion to solution. Then, oil fractions, dissolved in alkali, move towards the cathode with pore electro-osmotic solution and are more easily removed from the sample. It was found that higher alkalinity of the pore solution results in increase of decontamination efficiency as compared with sample containing NaCl neutral solution.

Thus, the application of an electrochemical leaching is more effective in comparison with the electrokinetic cleaning in the usual regime. Furthermore, according to obtained data it is possible to conclude that the use in this method of alkaline solutions as the extractant increases a quantity of moved away hydrocarbons. References [1] Korolev V.A. (2001). Laws of the electrochemical soils remediation from petroleum pollution. – EREM 2001. 3rd Symposium and Status Report on Electrokinetic Remediation / Schriftenreihe Angewandte Geologie Karlsruhe, 63, 19 (1-12) [2] Korolev V.A. (2001). The Cleaning of Soils from Pollution. – Moscow, MAIK/ Interperiodica publishing house, 365 pp. (in Russian) [3] Korolev V.A., Romanuha O.V. (2005). Research of Factors of the Electrokinetic Clearing Petropolluted Soil. - Mat-ls of VII Intern. Conf. “New Ideas in the Ground Sciences”, t 4, p. 21 (in Russian) [4] Korolev V.A., Romanuha O.V. (2006). The Electrokinetic clearing of soils from hydrocarbons as the factor of improvement of a resource quality of geological space of the urbanized territories. / Sergeev readings. Youth session. Materials of year session of Scientific advice of the RAS on problems of geoecology, engineering geology and hydrogeology , - Moscow, 8, pp. 128-131 (in Russian)

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ASSESSMENT OF ELECTROKINETIC METAL REMOVAL FROM BIOSOLIDS

Elektorowicz Maria1*, Hadhir Aboli1, Jan A. Oleszkiewicz2

1Department of Building, Civil, and Environmental Engineering, Concordia University, 1455 Blvd. de Maisonneuve West, Montreal, QC, Canada, H3G 1M8, [email protected] 2Department of Civil Engineering, University of Manitoba, 15 Gillson Street. Winnipeg, Canada R3V 1T9 Sludge is the end products of municipal wastewater treatment and contains many of the constituents removed from the influent wastewater. Wastewater treatment operations and processes produce sludge that typically contains from 0.25 to 12 percent solids by weight. Constituents of wastewater sludge include natural organics, nutrients, pathogens, metals, and anthropogenic organics. The sludge may undergo digestion or aerobic stabilization. During these processes, trace metals accumulate in the biosolids organic matter matrix and oxides of iron, aluminum or manganese, either through various phenomena (e.g. ion exchange, complexation). Concentrations of heavy metals in sewage sludge are one of the major issues of public concern when sludge is applied on land and may limit the sludge application rate and the useful life of the application site. Trace metals can accumulate in soils through repeated applications and become toxic to plants or lead to increased uptake of metals into the food chain. Recent regulations restrict disposal of biosolids. Thus, the removal of metals from biosolids is an essential and contemporary challenge for production of higher quality compost for agriculture and horticulture. In this study electrochemical methods were applied to metal removal from biosolids generated at wastewater treatment plant. The feasibility of using electrokinetic phenomena to metal removal was examined at lab scale with and without application of a conditioning liquid. The results showed that the effectiveness of metal removal was a function of the applied constant voltage, presence of conditioning liquid, and type of sludge. Thermodynamic software (Visual MINTEQ) was adapted to modeling of metals mobility in the sludge matrix. The modelling permitted to find the speciation and distribution of metals such as lead, zinc, nickel, cadmium, iron, and copper between electrodes for all applied conditions. The modelling helped define the best conditions for metal removal from sludge using electrokinetic phenomena. The results showed that application of the electrokinetic method of treatment could offer a unique, simple and reliable technology for upgrading biosolids to Excellent Quality product.

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ELECTROKINETIC REMOVAL OF BENTAZONE FROM SOILS: EXPERIMENTAL AND MODELING

A. B. Ribeiro1*, C. S. Abreu1, E. P. Mateus1, J. M. Rodríguez-Maroto2, M. D. R. Gomes da Silva3, H. K. Hansen4

1Departamento de Ciências e Engenharia do Ambiente, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, P-2829-516 Caparica, Portugal 2Departamento de Ingeniería Química, Facultat Ciencias, Universidad de Málaga, Campus de Teatinos, Málaga 29071, España 3 REQUIMTE, Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal 4Departamento de Procesos Químicos, Biotecnológicos y Ambientales, Universidad Técnica Federico Santa María, Av. España 1680, Valparaíso, Chile *Tel: (+351) 212 948 300 – Fax: (+351) 212 948 554 – E-mail: [email protected]

Abstract Rice crop fields are usually submitted to several pesticides during the rice cycle. One of them is the herbicide bentazone. The behaviour of bentazone in soils was studied when submitted to an electric field and the applicability of the electrokinetic process in bentazone soil remediation was evaluated. One soil, collected in the rice fields in central Portugal, was used. Since no old residues were detected from previous rice cycles, the soil was spiked with bentazone. Four electrokinetic experiments were carried out at a laboratory scale. Determination of bentazone residues were performed by HPLC. The results show that the electrokinetic process is able to remove bentazone in soil solution. A one-dimensional model was developed for simulating the electrokinetic treatment of a saturated soil containing bentazone. The movement of bentazone was modelized taking into account the diffusion transport resulting from bentazone concentration gradients and the eventual reversed electroosmotic flow at acidic soil pH. Keywords Electroremediation, herbicides, modeling, soil

122


ELECTROCHEMICAL DEGRADATION OF PAHs FROM WATER IN THE PRESENCE OF SURFACTANTS

T. Alcántara, J. Gómez, M. Pazos, S. Gouveia, C. Cameselle and M. A. Sanromán Department of Chemical Engineering. University of Vigo. 36310 Vigo. SPAIN E-mail: [email protected] Polycyclic aromatic hydrocarbons (PAHs) are widely distributed in the atmosphere. They are generally distributed from both natural (e.g. forest fires) and industrial sources. Many PAHs can have detrimental effect on the flora and fauna of affected habitats through uptake and accumulation in food chains, and in some instances, pose serious health problems and/or genetic defects in humans, so it is important to prevent the transport of these pollutants into the environment by remediation the source zones where high concentrations of PAHs exist. Toxic polycyclic aromatic hydrocarbons, such as Phenanthrene, Anthracene, and Pyrene, are persistent and difficult to remove from low permeability clayey soils because these contaminants have low aqueous solubility’s and a tendency to strongly bind with the clay minerals and organic matter present in these soils [1].

Many research efforts have been expended to find suitable method for remediation soil and water environments contaminated with PAHs. Among them, an environmentally friendly approach for PAHs degradation could be based on the use of electrochemical treatment, which is known to degrade a great variety of other polluted compounds such as dyes [2-3]. Liquid electrochemical oxidation is a versatile alternative that has the potential to replace or complete already existing processes. Nowadays, electrochemical technology is receiving more and more attention, for its success in degradation process without the production of a secondary pollutant and due to its convenience and simplicity. The exact mechanisms, which occur during the electrolysis, are complicated and not entirely clear. However, based on the intermediate products and radicals that can be determined in the electrolysis and other oxidants, it is postulated that organic pollutants could be oxidised directly or indirectly [4]. This treatment is compatible with the environment because the main reagent, the electron, is a clean one. Thus, the electrochemical oxidation is an environmental friendly and cost competitive alternative. Thus, electrochemical oxidation is a versatile alternative with a high potential to replace or improve existing processes.

A main problem on the treatment of PAHs in soil is their poor solubility in aqueous media. Therefore, the addition of different water miscible solvents such as surfactants must be considered as a previous step to enhance PAHs solubility. The PAHs are extracted with surfactants through a solid-liquid equilibrium extraction and the PAHs presents in the solution collected could be degraded by electrochemical treatment.

The objective of the present study is the evaluation of a system based on the sequence extraction-electrochemical treatment: extraction of PAHs from the spiked soil by an adequate surfactant followed by electrochemical degradation of PAH model compounds collected in the previous extraction stage. In first place, the selection of the most appropriate surfactants from a list of five (Brij 35, Tergitol, Tyloxapol, Tween 20, and Tween 80) was realized based on the extraction capacity for each PAH (Anthracene and Benzo[a]pyrene).

The electrochemical degradation of PAHs was studied using solutions of each PAH Anthracene or Benzo[a]pyrene at an initial concentration of 100µM, and Na2SO4 was

123

used like electrolyte for all of them with a concentration of 0.1M. Experiments were carried out in two electrochemical cells: A) Cubic Plexiglas cell with a working volume of 0.4 L, using graphite electrodes with an immersed area of 52 cm2, and an electrode gap of 8 cm. B) ECO-75 cell from Elchem GmbH has a working volume of 1.5 L, using titanium as cathode and titanium with special platinum coating as anode and surface of 560 cm2. In both cases a constant potential difference (5V) was applied with a power supply (HP model 3662) and the process was monitored with a multimeter (Fluke 175). Samples of reaction mixtures were taken from the electrochemical cells to be analyzed for pH and PAHs concentration. pH was measured with a Sentron pH meter (model 1001). The concentration of PAHs was achieved by using an Agilent 1100 HPLC equipped with a XDB-C8 reverse-phase column and using a diode array detector at 200 to 400 nm.

Initially, the PAHs desorption capacity to soil was evaluated. In Anthracene desorption studies have been determined that the highest level of removal for a concentration of 1 g L-1 was around 7.4 % for Tergitol. The desorbed value was increased up to 65.5 % when the concentration of this surfactant was augmented to 10 g L-1. However, the chromatograph obtained showed that the Anthracene peak was surrounded by numerous peaks that interfere in the measure of the concentration. Due to this, it must be chosen to subsequent experiments the surfactant Tyloxapol that showed a clear chromatograph and high removal level (47.5 %). In other hand, the levels of removal of Benzo[a]pyrene were near 84% and 80% when Brij 35 and Tween 80 (10 g L-1) were added, respectively. Thus, Brij 35 (10 g L-1) was selected as the better extracting agent.

The electrochemical treatment of PAHs-surfactant solutions obtained in the first stage were carried out in two electrochemical cells with different working volumes 0.4 or 1.5 L and electrode material (graphite or titanium). Time-course of treatment of Anthracene and Benzo[a]pyrene in solutions of Tyloxapol and Brij 35, respectively showed that in both cells similar profiles have been obtained. The kinetic studies of the degradation of the two PAHs fit well (regression 0.98-0.99) to exponential single with three parameters. On the other hand, it is widely recognized that the energy cost is the main drawback when it comes to applying electrochemical processes to the effluents treatment; therefore, the evaluation of both configuration showed a low cost with a medium value of electric power consumption around 0.27 Wh L-1 and 7.95 Wh L-1 to electrochemical treatment in cubic cell and ECO-75, respectively. Thus, the electrochemical oxidation of PAHs-surfactant solutions by electrochemical treatment is an environmental friendly and cost competitive alternative.

Acknowledgements: This research was financed by the Spanish Ministry of Science and Technology and European FEDER (Project CTM2004-01539/TECNO).

[1] Luthy, R. G., Aiken, G. R., Brusseau, M. L., Cunningham, S. D., Gschwend, P. M., Pignatello, P. M.,

Reinhard, M., Traina, S. J., Weber, W.J., Westall, J. C., 1997. Sequestration of hydrophobic organic contaminants by geosorbents. Environ. Sci. Technol. 31, 3341-3347.

[2] Sanroman, A., Pazos, M., Ricart, M. T., Cameselle, C., 2004. Electrochemical decolourisation of structurally different dyes. Chemosphere. 57, 233-239.

[3] Cameselle, C., Pazos, M., Sanroman, A., 2005. Selection of an electrolyte to enhance the electrochemical decolourisation of Indigo. Optimization and Scale-up. Chemosphere. 60, 1080-1086.

[4] Martínez-Huitle, C. A., Ferro, S., 2006. Electrochemical oxidation of organic pollutants for the wastewater treatment: Direct and indirect processes. Chemical Society Reviews. 35 (12): 1324-1340.

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ELECTROKINETIC REMEDIATION OF BENZO[a]PYRENE FROM CONTAMINATED KAOLINITE

J. Gómez, T. Alcántara, M. Pazos, C. Cameselle and M. A. Sanromán Department of Chemical Engineering. University of Vigo. 36310 Vigo. SPAIN E-mail: [email protected] Polycyclic aromatic hydrocarbons (PAHs) are pollutants of major concern in soils and sediments. These hydrocarbons are by-products of incomplete combustion or pyrolysis of organic materials with recalcitrance and strong mutagenic/carcinogenic properties [1]. Despite their very low solubility, once PAHs enter into soil, it is difficult to remediate by conventional treatment methods. Many research efforts have been expended to find suitable method for remediation soil and water environments contaminated with PAHs. Among them, an environmentally friendly approach for PAHs degradation could be based on the use of electrochemical treatment. Much effort is expended world-wide to develop new in-situ remediation methods or principles making remediation of contaminated soils faster and more effective. During the last few years, electrokinetic techniques have been applied successfully for the removal of organic contaminants [2].

In this work an in situ method that consists in the soil electrokinetic remediation had been evaluated in kaolinite spiked with PAHs. Toxic polycyclic aromatic hydrocarbons, such as Phenanthrene, Anthracene, and Pyrene, are persistent and difficult to remove from low permeability clayey soils because these contaminants have low aqueous solubility’s and a tendency to strongly bind with the clay minerals and organic matter present in these soils.

These compounds are electrically neutral, so they cannot be transported by electromigration, but they can be removed from the soil by electroosmosis. In order to increase the electroosmotic flow and desorption/solubilization of PAHs some surfactant or cosolvents could be added. The objective of the present study is to evaluate the potential of electro-remediation to remove a model PAHs (Benzo[a]pyrene) from a low permeability soil (such as kaolinite). In order to enhance desorption/solubilization of PAHs in soils mixed of cosolvent or surfactant (ethanol or Brij 35) and electrolyte Na2SO4 were evaluated.

The experiments were conducted in the electrokinetic cell (cylindrical glass) that contained a sample compartment of 100 mm length and 32 mm inner diameter. The two electrode chambers were placed at each end of the sample compartment isolated from this one by paper filter and porous stones. Graphite electrodes were used for both anode and cathode [3]. Three auxiliary electrodes allowed measuring the electric field distribution along the sample. Electrode chambers were filled with ethanol (40%) or Brij 35 (1%) and Na2SO4. Recirculation of liquid was applied by pumps to avoid concentration gradients. An electric field (3 V DC/cm) was applied across two inert electrodes of graphite, located at both sides of the soil sample. The soil was artificially contaminated (spiked) with Benzo[a]pyrene at a target concentration of 500 mg/kg (mass of PAHs/mass of dry soil).

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As can be seen in Figure 1, after thirty days, around 75.4% of initial Benzo[a]pyrene was removed from the soil using Brij 35 (1%) and Na2SO4 (0.1 M) as processing fluid (which enhanced the desorption of Benzo[a]pyrene from the kaolinite matrix) and operating with pH control at 4.5. Thus, the presence of Brij 35 and Na2SO4 increases the electric conductivity and favours the desorption of Benzo[a]pyrene from the clay particles. Moreover, the effect of the soil pH was demonstrated. It was very clear that the pH jump limited the current intensity and increased the electrical resistance of the system reducing the Benzo[a]pyrene transport.

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In view of the results obtained, it can be concluded that electrokinetic remediation appears to be a promising technique for the removal of PAHs from low permeability soils. However the operating conditions, especially the pH value into the soil sample, are decisive to achieve a full remediation.

Acknowledgements: This research was financed by the Spanish Ministry of Science and Technology and European FEDER (Project CTM2004-01539/TECNO).

[1] Joner, E.J., Johansen, A., Loibner, A.P., Cruz, M.A.D., Szolar, O.H.J., Portal, J.-M., Leyval, C.

Rhizosphere effects on microbial community structure and dissipation and toxicity of polycyclic aromatic hydrocarbons (PAHs) in spiked soil. (2001). Environmental Science and Technology, 35 (13): 2773-2777.

[2] Reddy, K.R., Ala, P.R., Sharma, S., Kumar, S.N. Enhanced electrokinetic remediation of contaminated manufactured gas plant soil. (2006) Engineering Geology, 85 (1-2): 132-146.

[3] Pazos, M., Sanromán, M.A., Cameselle, C. Improvement in electrokinetic remediation of heavy metal spiked kaolin with the polarity exchange technique. (2006). Chemosphere, 62 (5): 817-822.

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Figure 1. Electrokinetic treatment of Benzo-[a]pyrene contaminated kaolinite with/without pH control.

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ELECTROKINETIC REMEDIATION AND ELECTROCHEMICAL TREATMENT OF DYE POLLUTED KAOLINITE

M. Pazos, C. Cameselle and M. A. Sanromán Department of Chemical Engineering. University of Vigo. 36310 Vigo. SPAIN E-mail: [email protected] Dyes are organic colorants used in textile, pharmaceutical, cosmetic, food, and other industries for imparting different shades of colours. Dye manufacturers and users, particularly the textile industries, release wastewaters in massive quantities containing dye to the extent of 0.001-0.7% (w/v) [1].

Decolourisation of industrial textile effluents can be obtained by chemical, biological and physical methods. Each method has advantages and disadvantages. Biological processes show a limited colour removal due to the toxic nature of some dyes and the high salt concentration. Adsorption in activated carbon, membrane filtration, coagulation-flocculation and chemical oxidation with ozone have a considerable cost [2].

Sometimes, spilling and bad management of those effluents provoked the pollution of soils with this kind of organic pollutants. Biological, physical and chemical processes to remove organic pollutants have been considered for remediation of contaminated soils [3]. However, few reports about dye removal from polluted soils were found in the literature. Hence, there is a great interest in developing a soil remediation technology cost-effective and eco-friendly for those xenobiotic and recalcitrant organics.

In this work, it is proposed a novel technique that combined electrokinetic remediation and electrochemical treatment for the removal and degradation of textile dyes from polluted soils. The technique uses the electrokinetic remediation for the extraction of pollutants (dye) from soil. In a second stage, the electrochemical degradation is used to degrade the dye to simpler molecules, reaching even the total mineralization.

In order to test the feasibility of the combined purposed treatment, the electrokinetic remediation of kaolinite polluted with an acid diphenylnaphthylmethane dye Lissamine Green B (LGB) and the further electrochemical oxidation of the dye have been studied. The electrokinetic remediation was carried out in the electrokinetic cell (cylindrical glass) that contained a sample compartment of 100 mm length and 32 mm inner diameter. The two electrode chambers were placed at each end of the sample compartment isolated from this one by paper filter and porous stones. Graphite electrodes were used for both anode and cathode [2]. An electric field (3 V DC/cm) was applied across two inert electrodes of graphite, located at both sides of the soil sample. The soil was artificially contaminated (spiked) with LGB at a target concentration of 0.225 g dye kg-1 of dry matter, and its pH was around 4 in all the experiments. The moisture content was around 32%, expressed as weight of water per unit weight of wet kaolinite.

The unenhanced electrokinetic treatment did not result in any significant removal of LGB from the kaolinite sample. However, the use of Na2HPO4 as processing fluid increased the electro-osmotic flux, improved the desorption of dye from the surface of kaolinite particles and prevented the acidification of the medium. It resulted in the transportation of 94% of the dye towards the cathode chamber where it was

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accumulated (Figure 1). The use of K2SO4 in the processing fluid also improve the results compared to the unenhanded experiment but the removal of dye only reached

75% due to the lower electro-osmotic flux registered in this experiment.

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Once the dye was removed from kaolinite clay sample, the dye Lissamine Green B can be decolourized upon the electrodes. This process was studied at different dye concentrations (7.5 – 150 mg L-1) and with disodium hydrogen phosphate (0 – 0.01 M) as electrolyte. The presence of Na2HPO4 clearly improves the degradation rate reaching 90% of decolourization in 90 min.

Figure 1. Electrokinetic treatment of LGB spiked kaolinite with Na2HPO4 as processing fluid in the cathode and anode chamber. Normalized concentration (bar) and pH (line).

The results obtained in this work have clearly shown that by the used of this combined treatment, full remediation of dye polluted kaolinite at low cost without operational problems, can be achieved. Therefore, this technique may be an attractive option for treatment of industrial wastes (water and ground) contaminated with dyes. Moreover, the process was improved by addition of an adequate electrolyte such as disodium hydrogen phosphate. This electrolyte has a double utility as:

Processing fluid in electrokinetic treatment: its presence in the cathode and anode chambers favoured the electric conductivity and the desorption of LGB in the soil.

Electrolyte in electrochemical treatment: there is a relationship between the decolourization rate and electrolyte concentration. When the disodium hydrogen phosphate concentration is augmented, the dye decolourization rate increased.

Thus, operating at the optimized conditions determined in the present study an appropriated configuration was designed and the full remediation of polluted kaolin at low cost without operational problems can be achieved.

Acknowledgements: This research was funded by Xunta de Galicia (Project PGIDIT04TAM314003PR).

[1] Zollinger, H. Color Chemistry-Syntheses, Properties and Applications of Organic Dyes and Pigments.

3rd Ed. Wiley-VCH, 2003. [2] Pazos M, Ricart MT, Sanromán MA, Cameselle C. Enhanced electrokinetic remediation of polluted

kaolinite with an azo dye. Electrochimica Acta 2007; 52(10): 3393-3398. [3] Gong Z, Wilke BM, Alef K, Li P, Zhou Q. Removal of polycyclic aromatic hydrocarbons from

manufactured gas plant-contaminated soils using sunflower oil: Laboratory column experiments. Chemosphere 2006; 62(5):780-787.

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REMOVAL OF ORGANIC POLLUTANTS AND HEAVY METALS IN SOILS BY ELECTROKINETIC REMEDIATION

M.T. Ricart, M. Pazos, S. Gouveia, C. Cameselle and M.A. Sanromán Department of Chemical Engineering. University of Vigo. 36310 Vigo. SPAIN E-mail: [email protected] The wrong management of the industrial wastes in the past had dealt to the pollution of the surrounding areas of industrial sites. Often, the pollution includes inorganic salts, heavy metals, complex organic compounds, etc. Very few technologies (soil washing…) can be applied for the removal of heavy metals and organic pollutants from soil and solid wastes, and in many cases they do not success mainly due to the longer treatment time and the high cost involved.

Literature had proved that electrokinetic remediation has the potential to remove either heavy metals or organic compounds from soils, sediments and solid wastes. However, very few research groups deal with the simultaneous removal of organics and heavy metals [1-3]. The different nature of both types of pollutants and their possible interaction made difficult to optimize the operating conditions for their extraction and transportation out of the soil.

The aim of this work is to evaluate the feasibility of the electrokinetic treatment of solid matrixes polluted with organics and heavy metals. Tannery industry produces wastes with a high content of chromium and a complex organic pollution, mainly dyes. Chromium is a dangerous heavy metal found in the tannery industry wastes in high concentration. Moreover, about 15% of total world production of wastewater in textile dyeing/finishing and also in food, paper and cosmetic industries are lost in its effluents. The discharge of these highly coloured wastewaters into the ecosystem involves environmental problems. There are more than 10000 of chemically different dyes synthetic and pigments. Among them, azo dyes are a major class of synthetic, coloured organic compounds and account for about half of the textile dyestuffs used today [4].

The optimization of the electrokinetic treatment of this waste is rather difficult due to its complexity in composition and the possible interactions among its components. Therefore, the application of electrokinetics in this kind of wastes was firstly tested in model samples at bench scale. These model samples were prepared with kaolinite clay polluted with Cr and an azo dye such as Reactive Black 5 (RB5).

RB5 is a dye commonly used in the industry, its complex structure with several aromatic rings and two azo bonds, make it appropriate as a model organic pollutant. In previous paper, Pazos et al. [5] have determined that the electrokinetic treatment of the RB5 spiked kaolinite sample can result in a complete cleaning of the kaolinite matrix if the operating conditions are adjusted properly. The presence in the processing fluid of salts, which favour RB5 desorption from the kaolinite matrix, and the operation at alkaline pH (which favours the ionization of the molecule), enhanced the migration towards the anode, where the dye is accumulated.

On the other hand, the removal of heavy metals by electrokinetics can be achieved in acidic conditions, since low pH favours the solution of metals and they form cationic species that migrate towards the cathode. It is obvious that the optimum conditions for removal of Cr and RB5 do not mach up.

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In order to improve this electrokinetic process, it is necessary to add an electrolyte that increases the electric conductivity and favours the desorption of dye from the polluted clay sample. Potassium sulphate was found to have been very effective in the extraction of dye from the mineral matrix and its presence increases the electric conductivity and favours the desorption of RB5 from the clay particles. In these experiments potassium sulphate was selected as processing fluid, filling the anode and cathode chamber with 0.1 M potassium sulphate.

The operating conditions, especially the pH value into the soil sample, are decisive to achieve a full remediation. It was determined that near complete cleaning of the kaolinite matrix could be obtained when electrokinetic treatment was carried out with pH control on anode. When pH value was controlled at 7±0.2 on the anode chamber it avoided the formation of an acid environment at the anode side and favoured the advance of the basic front. So, the kaolin sample was alkalised reaching an almost flat pH profile (from 9.2 to 9.6). As can be seen in figure 1, 97% of the initial RB5 was removed from kaolinite by electromigration towards the anode, where the dye was oxidized upon the surface of the electrode by electrochemical oxidation. On the other hand, Cr was transported towards the cathode by electromigration as a cation but also by electroosmosis. About 96% of initial Cr was found in the cathode chamber as a precipitated due to the high pH in the cathodic solution. Only 4% of Cr remained in kaolinite.

From these results, it is supposed that the interaction among RB5 and Cr into the kaolinite sample avoid the usual premature precipitation of Cr into the soil and favors its migration and concentrate in the cathode chamber.

FFigure 1.- Electrokinetic treatment of RB5 and Chromium spiked

kaolinite with pH control in the anode

Soil Section (anode-cathode)

A B C D E0

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Acknowledgements: This research was funded by Xunta de Galicia (Project PGIDIT04TAM314003PR).

[1] Maturi K, Reddy KR. (2006) Simultaneous removal of organic compounds and heavy metals from

soils by electrokinetic remdiation with a modified cyclodextrin. Chemosphere 63 (6), 1022-1031. [2] Reddy KR, Karri MR. (2006) Effect of voltage gradient on integrated electrochemical remediation of

contaminant mixtures. Land Contamination and Reclamation 14 (3), 685-698. [3] Maini G, Sharman AK, Knowles CJ, Sunderland G, Jackman SA. (2000) Electrokinetic remediation

of metals and organics from historically contaminated soil. Journal Chemical Technology Biotechnology 75 (8), 657-664.

[4] Zollinger, H. (2003) Color Chemistry-Syntheses, Properties and Applications of Organic Dyes and Pigments. 3rd Ed. Wiley-VCH.

[5] Pazos M, Ricart MT, Sanromán MA, Cameselle C. (2007) Enhanced electrokinetic remediation of polluted kaolinite with an azo dye. Electrochimica Acta 52(10): 3393-3398.

Com

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ELECTROKINETIC DESORPTION PROCESSES OF SOFT SOIL CONTAMINATED WITH HEAVY METAL

MyungHo Leea, Jung-Geun Hanb and Jai-Young Leec aBK Research Associate, Dept. of Civil & Environ. Eng., Hanyang Univ., South Korea E-mail: [email protected] bAssociate Professor, Dept. of Civil & Environ. Eng., Chung-Ang Univ., South Korea cAssociate Professor, Dept. of Environ. Eng., Univ. of Seoul, South Korea

ABSTRACT

This paper presents several aspects of soft soil behaviour under the influence of electric field using kaolin clay. A number of batch equilibrium tests and electrokinetic column experiments were carried out with zinc spiked slurries in order to investigate the migration of heavy metal contaminants and their removal efficiency during the electrokinetic soil processing. Sorption and Desorption characteristics of zinc spiked soft soils have been examined and evaluated by comparison with the electrically induced desorption and precipitation occurring in the anode and cathode regions, respectively. The removal efficiency of zinc under the applied voltage gradient of about 300 V/m was found to be up to approximately 95 % in the anode region within 6 hours of the electrokinetic treatment.

Keywords: cohesive soil, desorption, electrokinetics, pH, removal efficiency

Fig. 1. Electrokinetic reactor in use

EOFlow

Effluent

VoltageProbe

Anode

Hydraulic Head Equalizer (HHE)

From HHE

Cathode

DCPower Supply


Poster 20

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Fig. 2. Sorbed zinc concentration after electrokinetic processes as a function of normalised distance from cathode

Fig. 3. Aqueous zinc concentration after electrokinetic processes as a function of normalised distance from cathode


[2] Hamed, J., Acar, Y. B. and Gale, R. J. (1991), “Pb(II) removal from kaolinite by electrokinetics”, J. Geotech. Eng., 117(2), pp. 241-271.

[3] Mitchell, J. K. (1993), “Fundamentals of soil behaviour”, Wiley Inter. Science [4] Pamukcu, S. and Wittle, J. K. (1992), “Electrokinetic removal of selected heavy

metals from soil”, Environmental Progress, 11, pp. 241-250. [5] Yeung, A. T. (1994), “Electrokinetic flow processes in porous media and their

applications”, Advances in porous media, Elsevier, 2, pp. 309-395.

0

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ELECTROKINETIC BLEACHING OF KAOLIN CLAY C. Cameselle, M. Pazos, I. Vazquez, F. Moscoso and M. A. Sanromán Department of Chemical Engineering. University of Vigo. 36310 Vigo. SPAIN E-mail: [email protected]

Kaolin is widely used as a raw material in the ceramic industry and as an additive in the pulp and paper industry. Both applications require a clear whiteness. Iron oxides reduce the whiteness index of kaolin giving a brown-yellow coloration depending on the concentration of contaminant iron. Under these conditions the kaolin is useless for industrial applications and it becomes necessary to apply a bleaching process [1].

Currently, different methods are used to remove mineral iron, so that the kaolin reaches an adequate whiteness index for industrial applications. Chemical methods [2] are based on the reduction of ferric iron to ferrous iron by reducing agents (sodium dithionite, sulphur dioxide, sodium acid sulphide) at low pH. A treatment with complexing agents prevents later reoxidation from ferrous to ferric iron, avoiding the undesirable colour formation. If the kaolin is used in the ceramic industry, the iron should be extracted because it will be oxidized to ferric iron during the kilning phase, appearing as ferruginous spots.

Chemical methods are suitable to achieve high yields of iron removal and high whiteness indices, but they are harsh for the environment. The quantity of chemical reagents used in the bleaching process may be minimized in order to obtain economical benefits because they are expansive and the price of kaolin is low [3].

The electrokinetic treatment could be a possible alternative for bleaching the kaolin. The application of an electric field to a sample of low grade kaolin polluted with iron (ferric oxides and hydroxides) could dissolve the ferric iron and transport the Fe3+ ions towards the cathode, removing them from the kaolin, so that, this clay would reach a high whiteness index, appropriate for its common applications, including high quality ceramics.

The direct application of the electric field to iron polluted kaolin shows a limited effectiveness since the acid front generated at the anode is not able to dissolve effectively some ferric oxides and the ferric hydroxides requires a very low pH to be dissolved completely. It is due to the low value of the formation equilibrium constant of Fe(III) hydroxide (pKs=37) and the stability of the hydroxide is from pH as low as 2 to 14. Furthermore, the basic front immobilized the iron in the region of sample close to the cathode.

The electrokinetic treatment of iron polluted kaolin can be improved controlling the pH in the cathode chamber. Thus, the acidification of the kaolin sample by the acid front will be effective dissolving the iron throughout the sample, reaching a very low pH value. In order to limit the electric consumption, the pH in the cathode was adjusted at 6. Lower pH results in higher electric power consumption and the overall process of kaolin bleaching could be non-profitable. The limitation in the pH value in the cathode does not affect negatively to the acidification of the kaolin sample that reaches a pH between 2 and 3.

The extraction and solubilisation of the iron can also be improved with the addition of complexing agents in the electrode chambers. These compounds will be transported towards the kaolin sample by electroosmosis and electromigration. Several compounds

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were tested for the extraction of iron from kaolin, mainly organic acids [4]. Among the organic acids tested (citric acid, gluconic acid,…) only oxalic acid shows a good activity releasing and dissolving the iron from kaolin. The best results were found at low pH and with high oxalic acid concentrations.

Oxalic acid dissolves iron from kaolin by direct attack of H+ ions to the minerals that contains iron. Once the iron is in solution as Fe3+, oxalic acid forms a soluble complex that stabilises the metal in solution and prevents its precipitation. It was found a ratio between the amount of oxalic acid used in the extractions and the amount of iron in solution. 3 mol of oxalic acid are needed for dissolving 1 mol of iron. It suggests the formula of the soluble complex (equation 1)

3 (C2O4)2- + Fe3+ ⎯⎯→ [Fe(C2O4)3]3- [eq 1]

In the this soluble complex, iron, as ferric ion Fe3+, is bonded to three oxalate ions by one of the oxygens corresponding to the acid groups. The complex has a yellow colour, the same as the supernatant after the leaching of kaolin. The oxalate ion in the complex is oxidized by the action of Fe3+ ion in a reaction catalyzed by light, resulting CO2 and ferrous oxalate, which forms a brown precipitate (equation 2). This explains the precipitate formation after the leaching process is completed. The complex is stable when maintained in darkness. The formation of a precipitate of ferrous oxalate removes the iron from the effluent from a leaching process, so avoiding environmental problems and simplifying effluent treatment.

[Fe(C2O4)3]3- C2O4Fe↓ + 4 CO2 [eq. 2] ⎯⎯→⎯light

The electrokinetic treatment of iron polluted kaolin was carried out with pH control at 6 in the cathode to suppress the acid front. The electrode chamber were filled oxalic acid 0.1M that acted as electrolyte favouring the electric conductiviy of the system and also favours the extraction and complexation of the iron. Most of the iron was recovered in the cathode assuring the formation of the negatively charged complex. Operating in these conditions the iron was removed from kaolin and its whiteness index increased up to 80% (measured as light reflexion using boric acid as reference for 100% of whiteness). This value is adequate for the main industrial applications of kaolin.

Acknowledgements: This research was financed by the Spanish Ministry of Environment (Project number: 294/2006/1-1.2).

[1] Ribeiro, F.R., Mussel, W.N., Fabris, J.D., Novais, R.F., Garg, V.K. Identification of Iron-Bearing Minerals in Solid Residues from Industrial Kaolin Processing. Hyperfine Interactions 148-149 (1-4): 47-52. [2] Vegliò, F., Passariello, B., Toro, L., Marabini, A.M. (1996). Development of a bleaching process for a kaolin of industrial interest by oxalic, ascorbic, and sulfuric acids: Preliminary study using statistical methods of experimental design. Industrial and Engineering Chemistry Research 35 (5), pp. 1680-1687 [4] C. Cameselle, M.J. Núñez, J.M. Lema. (1997). Leaching of kaolin iron-oxides with organic acids. Journal of Chemical Technology and Biotechnology 70 (4): 349-354. [3] Cameselle, C., Ricart, M.T., Núñez, M.J., Lema, J.M. (2003). Iron removal from kaolin. Comparison between "in situ" and "two-stage" bioleaching processes. Hydrometallurgy 68 (1-3): 97-105

134


ELECTROMIGRATION OF Mn, Fe, Cu AND Zn WITH CITRIC ACID IN POLLUTED CLAY

M. Pazos, A. Huerga, J. L. Prieto, S. Gouveia, M. A. Sanromán, C. Cameselle Department of Chemical Engineering. University of Vigo. 36310 Vigo. SPAIN E-mail: [email protected]

The metal reactivity, speciation and solubility have an important influence in the electroremediation efficiency. This work deals with the effect of solubility and transport competition among different metals (Mn, Fe, Cu and Zn) during their transport through contaminated clay. In order to avoid the negative effects of the basic front generated at the cathode, two different techniques were proposed and tested. Both techniques were based on the capability of citric acid to act as a complexing or neutralising agent.

Three experiments were carried out with a kaolin clay matrix contaminated with Fe, Mn, Cu and Zn. These metals were selected since they were found in several industrial wastes (Ricart et al., 2004). Citric acid was used to depolarise the cathodic reduction of water (Exp. 3) and was added to the soil matrix as a complexing agent (Exp. 2). The influence of citric acid in those experiments was compared with a control experiment (Exp. 1).

In the control experiment (Exp. 1) metals migrated towards the cathode showing different removal: 75.6% Mn, 68.5% Zn, 40.6% Cu and 14.8% Fe. The residual metal in soil remained mainly in the last section, close to the cathode, where it was found 35% of the initial Fe and Cu. The differences in the transportation and extraction from the soil were due to the formation of the corresponding metal hydroxides. Ferric hydroxide presents the lowest solubility product, so this is the first metal to precipitate due to the alkaline front that penetrates into the soil from the cathode. Opposite, Mn shows the highest solubility product and achieves the cathodic chamber more easily since its hydroxide is formed at higher pH. Cu and Zn showed elimination in accordance with their solubility product.

Further experiments were carried out with the addition of citric acid with the aim of suppress the negative effect of the alkaline front generated at the cathode. Citric acid was used to control de pH in the cathode (Exp. 3) and it was mixed with the soil sample to complex metals (Exp. 2).

In experiment 2, Cu, Zn and Mn were complete removed from the soil and were concentrated in the cathode chamber. Fe elimination was lower than the other metals, only 34% reached the cathode. However, there was a significant increase in the Fe elimination compared to the control experiment. The pH in the soil during the experiment is about 3. In this condition, Cu, Zn and Mn form positive or neutral complexes. These species were transported to the cathode side by electromigration and electroosmosis. Fe3+ forms a negative complex with citric acid (Fe2(OH)2L2

2-) under this pH condition. This complex would reach the anode if the only transport process were electromigration. Since the metal was concentrated on the cathode side, it can be concluded that electroosmosis was the primary transport mechanism and electromigration played a secondary role. It was confirmed by the large electro-osmotic flow detected during the experiment. A total volume of 124 ml flowed through the soil during the 7 days of treatment, which correspond with 4 times the volume of pore fluid. A negligible electroosmotic flow was detected in the control experiment. The increase of the electroosmotic flow is related to the presence of citric acid in the soil [1].

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Whereas the citric-Fe complex migrates towards the anode, the electroosmotic flow carries Fe to cathode chamber. Fe transportation will be slower than the other metals because of the electromigration in the opposite direction.

In experiment 3, citric acid was used to control de pH in the cathode chamber. So, citric acid acted as neutralising and complexing agent. When pH control was carried out with mineral acids (sulphuric or nitric acid) a precipitated of difficult handling was formed [2] because the metal undergoes further reactions on the electrode. Using citric acid, this precipitated is not created, because citric acid maintains the metal in its soluble form and protect them from further reactions on the electrode. It makes the subsequent handling and treatment easier. Nevertheless Cu was electroplated on the cathode what means that it was separated with a good quality and its recovery can be a possibility. As well as experiment 2, the elimination of Cu, Zn and Mn was complete using citric acid as depolarised agent. On the other hand, the elimination of Fe was poor, similar to that obtained in the control experiment. Fe3+ migrated in the direction of the cathode, while the citrate added to the cathode chamber migrates through the soil in direction to the anode. Citrate principally formed a complex with iron because of the high value of the formation constant. Under the pH conditions into the soil, the citrate-Fe(III) complex is negatively charged and tended to migrate to the anode, although it moved slowly due to its big size. After 7 days of treatment, citrate and iron were principally concentrated in the sections 4th and 5th (the closest to the cathode) as it can be seen in Figure 1.

No significant electroosmotic flow was observed in this experiment confirming that the primary transport mechanism was electromigration. When citric acid is added in the electrode chambers no electroosmotic flow change was observed, as it was also reported by Zhou et al. [3], this confirming that the citric concentration in the soil is an important factor to enhance the electroosmosis [1, 4].

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Acknowledgements: This research was financed by the Spanish Ministry of Environment (Project number: 294/2006/1-1.2).

[1] Popov, K.I., Shabanova, N.A., Artemeva, A.A., Urinovich, E.M. and Tulaeva, Y.V. (1997). Influence of Chelating Agents on the Electrokinetic Potential of the Clay Fraction of Soddy Podzolic Soils. Colloid J. 59 (2), 212-214. [2] Pazos, M. (2002). Remediación electrocinética de suelos contaminados con Mn en condiciones de pH controladas. Master Thesis. Department of Chemical Engineering, University of Vigo. [3] Zhou, D.M., Zorn, R. and Kurt, C. (2003). Electrochemical remediation of copper contaminated kaolinite by conditioning anolyte and catholyte pH simultaneously. J Environ. Sci.-China 15 (3), 396-400.

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ELECTRODIALYTIC REMEDIATION OF SUSPENDED MINE TAILINGS

Henrik K. Hansen1, Adrian Rojo1, Lisbeth M. Ottosen2, Alexandra Ribeiro3

1Departamento de Procesos Químicos, Biotecnológicos y Ambientales, Universidad Técnica Federico Santa María, Casilla 110-V, Valparaíso, Chile 2Department of Civil Engineering, Building 118, Technical University of Denmark, 2800 Lyngby, Denmark 3Departamento de Ciências e Engenharia do Ambiente, Faculdade de Cadencies e Technologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal E-mail: [email protected] Mining activities in Chile have generated large amounts of solid waste, which have been deposited in mine tailings impoundments. These impoundments cause concern to the communities due to dam failures or natural leaching to groundwater and rivers. The need for remediation or control of these wastes is obvious. Electrokinetic remediation has shown its potential for remediation of a great variety of solid waste materials. A possible mine tailings treament is based on the electrodialytic remediation principle [1], where the introduction of ion exchange membranes improves the electrokinetic remediation process. Electroremediation - both electrokinetic (EKR) or electrodialytic (EDR) - could also be promising with mine tailings. Furthermore, the recovery of metal from the mine tailings could mean a profitable solution. Hansen et al. [2] showed that copper could be removed from tailings using electrodialytic remediation but the process had to be enhanced by optimizing the treatment conditions. One of the most concerning parameters was the remediation time. Lately, Ferreira et al. [3] have shown that the remediation time can be decreased remarkably when treating the solid waste material in suspension. The idea was to have the solid suspended by mechanical stirring in an electrical conducting liquid – typically with a liquid-to-solid ratio between 5 and 10. The dissolution is rapid, and thereby the electromigration of dissolved heavy metals towards the electrodes too. The system is homogenous and no concentration and pH gradients are generated in the transport medium. No electroosmosis – as in the case of static electroremediation – will occur, only transport of ions. The results show that even if the solid material to be treated is occupying a fifth of the volume compared to static electroremediation, the remediation time is shortened by a factor of 20. This means that the overall remediation time for a certain mass to be treated is four times shorter in the suspended cell than with the static cell.

The present work suggests the use of neumatical stirring instead of mechanical stirring. The use of air as a stirrer to produce the suspension also provides an oxidizing condition for certain heavy metal species such as sulphides present in tailings. Figure 1 shows the principle in electrodialytic remediation, where the solid waste material is suspended in compartment III. The fine porous material in suspension is stirred by the air flow introduced at the bottom of the cell. The electric field is generated between the anode (comp. I) and cathode (comp. V), and the heavy metal cations, which are released fast to the solution, are transported across membrane c into compartment IV. Here heavy metal

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air

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cathode anode

Cu2+

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d c b a

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Figure 2. General principle of electrodialytic remediation in suspended cell. will continuously be removed from the solution by ion exchange resin, which on the other hand will release protons to neutralize OH- coming from compartment V (cathode reaction). This work shows the laboratory results of six electrodialytic remediation experiments on copper mine tailings. The results show that electric current could remove copper from watery tailings applying 42 mA during 7 days. The liquid-to-solid ratios used were 3, 6 and 9. With addition of sulphuric acid, the process was enhanced because the pH decreased to around 4, and the copper by this reason was released in the solution. The maximum copper removal was 53% with addition of sulphuric acid in 7 days experiment at 42 mA using approximately 137.5 g mine tailings on dry basis. The removal for a static (baseline) experiment only reached 12 % when passing approximately the same amount of charge through 130 g of mine tailings. The use of air bubbling (as stirring mechanism) increased the removal efficiency from 30 % to 53 % compared to no stirring maintaining other operation conditions the same.

[1] Hansen et al., Journal of Chemical Technology and Biotechnology 70 (1997) 67-73. [2] Hansen et al., Journal of Hazardous Materials 117 (2005) 179-183. [3] Ferreira et al., Engineering Geology 77 (2005), 339–347.

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ELECTRODIALYTIC REMEDIATION OF COPPER MINE TAILINGS USING BIPOLAR ELECTRODES.

Adrián Rojo1, Henrik K. Hansen1. 1Departamento de Procesos Químicos, Biotecnológicos y Ambientales, Universidad Técnica Federico Santa María, Casilla 110-V, Valparaíso, Chile E-mail: [email protected] The present work shows how an electrodialytic remediation (EDR) cell for the copper mine tailings improves the remediation action. In this cell bipolar stainless steel plates were used [1], and they were inserted inside the tailings dividing it in independent electrochemical cells, called sections. This work shows the laboratory results of seven electrodialytic remediation experiments on copper mine tailings. The use of bipolar plates was tested with:

• an electric field of 20[V] • a dry sample of 1.45 kg • a water content of 20% adjusted using distilled water and/or citric acid • an initial pH of 4 • a remediation time of 18 days (exception experiment 7 with 3 days)

Each tailing section was divided in three zones: anode, center and cathode, in order to evaluate copper removal. Table 1 shows a summary of the experiemental.

Table 1. Summary of experimental results. Exp. Pre-treatment/

Nº bipolar plates Removal

anode zone (%)

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(%)

Accumulation catho one de z

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Current effi ciency

Center zone (%)

Current e fficiencyCathode

zone (%)

1 Distilled water / 0 9.4 0.6 (10.0) 0.3 0.02 (0.3) 2 Citric acid / 0 9.9 1.5 (15.4) 0.2 0.1 (0.4) 3 Di 1 stilled water / 10.9 1.9 (12.3) 0.8 0.2 (1.0) 4 Citric acid / 1 13.0 2.6 (16.5) 0.7 0.1 (0.8) 5 Di 3 stilled water / 11.4 2.6 (16.8) 1.3 0.6 (1.9) 6 Citric acid / 3 15.8 5.2 (24.7) 1.3 0.4 (1.7) 7 Distilled water / 1 8.7 (1.4) (8.3) 5.3 (0.8) (4.5) Bipolar plates in electrodialytic remediation (EDR) of copper mine tailings improves the remediation action. This fact occurs even though the electric field is reduced when implementing bipolar electrodes, since some of the electric field is consumed by the electrochemical reactions on the plates. Basically three aspects that improved the process were found: i) reduction of the pathways of ionic migration, ii) increase of the electrode surface and iii) in-situ generation of protons (H+) and hydroxyls (OH-). The citric acid addition together with 1 or 3 bipolar electrodes improved even more the remediation action, reaching copper removal in the anode and center zone up to nine times better, compared to conventional experiences EDR without any plates or addition of citric acid [2,3].

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Removal obtained in the anode zone as in the center zone could be improved increasing the the remediation time further than 18 days. This is due to the fact that there would still exist a margin to continue removing copper from tailing. These major times of EDR would furthermore be useful to increase the removal in the tailing’s center zone and, for this reason, to get finally a major amount of remedied material. In addition, the acid and alkaline fronts which are generated when using bipolar plates should reduce the tailing neutralization time’s posteriors for having a minor migration pathway.

[1] Hansen, H.K., Rojo, A., Ottosen, L.M., Electrochimica Acta, 52 (2007) 3355-3359. [2] Hansen, H.K., Rojo, A., Ottosen, L.M., Journal of Hazardous Materials 117 (2005) 179. [3] Rojo, A., Hansen, H.K., Separation Science and Technology 40(9) (2005) 1947.

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ENHANCED ELECTROKINETIC SOIL REMEDIATION OF HEAVY METALS

Ayten Genca, George Chaseb

aDepartment of Environmental Engineering, Zonguldak Karaelmas University, 67100 Zonguldak, Turkey; bDepartment of Chemical and Biomoleculer Engineering, The University of Akron, Akron, Ohio 44325-3906 E-mail: [email protected] Abstract

The removal of manganese, copper, zinc, and lead from naturally polluted sediments were investigated by performing electrokinetic remediation experiments. The pH in both electrode cells was controlled by using 0.1 M acetic acid solution during the electrokinetic remediation experiments. It was observed that the transport of metals in the sediment by the application electric field were different. Manganese accumulated in closer areas to cathode. For copper, zinc and lead, however, the accumulation was mostly observed in the middle section of the sediment, i.e., areas away from both electrodes. It is postulated that having alkaline sediment and reverse electroosmotic flow could be the reasons for the accumulation of metal ions in the middle section.

1. Introduction

Electrokinetic remediation is a process that separates and extracts heavy metals, radionuclides, and organic contaminants from saturated or unsaturated clay-rich soils, sludges, and sediments under the influence of an applied electric field. Experiments have shown its applicability to a variety of organic, inorganic and radioactive wastes ([1], [2], [3] and [4]). Electrokinetic remediation involves applying a low direct current or a low potential gradient to a pair of electrodes that are inserted into the soil. Due to water electrolysis at the electrodes, hydrogen and hydroxyl ions form. When these ions enter the soil and move by the electric field, a sudden pH change appears in the soil, which can cause metal ions to precipitate. In order to solve this problem, various enhancement techniques have been proposed and implemented in the literature. In this study, the control of pH in anode and cathode electrode cells was studied as an enhancement technique in the electrokinetic remediation in order to remove manganese, copper, zinc and lead from river sediment, which were obtained from the Cuyahoga River, Ohio. The sediment was alkaline and had 20% clay, which was mainly illite. The organic content of the sediment was 13.4% and the initial concentrations of manganese, copper, zinc and lead in the sediment were 355, 190, 92 and 43 mg/kg, respectively. The experimental apparatus consisted of an electrokinetic cell, anode and cathode tanks, pumps and a power supply (0-600V, 0-1.7A). In the middle section of the electrokinetic cell, the soil was inserted in a tube made of Lexan (ID: 6.36cm and L: 20cm). The volume capacities of the electrode cells were 50ml and were placed at both ends of the electrokinetic cell. Two graphite discs, 7.62cm in diameter and 0.635cm in thickness, were used as anode and cathode electrodes. The liquids in both electrode cells were circulated from the electrode cells to the corresponding electrode tank by using 1/55-hp magnetic drive pumps. The circulation flow rates at both tanks were controlled in the

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range of 10-15 ml/s. The anode and cathode tanks had the volume capacity of 2 liters each and 1500ml of liquid was always present in the tanks during the experiments. In the first electrokinetic remediation experiment, pH values in anode and cathode electrode cells were kept constant at 4. In the anode cell, pH was adjusted to 4 by acetic acid at the start of the experiment and tap water was added when a decrease in pH was observed. On the other hand, the control of pH in the cathode cell was adjusted by circulating 0.1 M acetic acid solution. After the adjustment of pH in both electrode cells a constant current of 50 mA was applied to the sediment specimen. In the second electroremediation experiment, only the applied current was changed and increased to 70 mA. 2. Results

The residual manganese, zinc, copper and lead concentrations in the sediment with recpect to the distance from anode were evaluated by using atomic absorption spectrometer measurements. The lowest amount of manganese (38.6 mg/kg) was observed close to the anode. In addition, close to the cathode the residual manganese concentration (480 mg/kg) was higher than the amount present in the original sediment (355 mg/kg). These observations clearly indicate manganese ions are transported toward to cathode. For copper, zinc and lead, however, the accumulation was observed in the middle section of the sediment. Because of having alkaline sediment, it might take additional time to observe desorption of the metals due to the acidity of the soil, especially in the middle section of the sediment sample. In addition, the reverse electroosmotic flow were observed during the experiments and its direction changed periodically. Therefore, having alkaline sediment, controlling pH at both ends and reverse electroosmotic flow could be some of the reasons for the accumulation of metal ions in the middle. It is also concluded that manganese is mainly present in the form of metal acetates (MnAc+) in the pore fluid and therefore, they only move toward the cathode. When the applied current to the sediment specimen was increased from 50 mA to 70 mA in addition to pH control at electrode cells, no increase in the removal efficiency of metals was observed. Therefore, increasing electric field strength does not necessarily mean an increase in the removal efficiency. The calculated removal efficiencies of manganese, copper, lead and zinc were 18%, 20%, 12%, and almost zero, respectively. On the other hand, depending on the experimental results, the control of pH at both electrode cells can decrease the electrical potential difference across the electrodes in comparison to un-enhanced electrokinetic remediation, and this can result in energy saving. [1] Y.B. Acar and A.N., and A.N. Alshawabkeh, Principles of Elektrokinetic Remediation”, Environmental Science and Technology 27 (1993) 2638-2647. [2] S. O. Kim, K.W. Kim, D. Stuben, Evaluation of Electrokinetic Removal of Heavy Metals, Journal of Environmental Engineering 28 (2002)705-715 [3] D. Turer, A. Genc, Assessing effects of electrode configuration on the efficiency of electrokinetic remediation by sequential extraction analysis, Journal of Hazardous Materials B119 (2005) 167-174. [4] A. Giannis, E. Gidarakos, Washing enhanced electrokinetic remediation for removal cadmium from real contaminated soil, Journal of Hazardous Materials B123 (2005) 165-175.

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PRELIMINARY TREATMENT OF MSW FLY ASH AS A WAY OF IMPROVING ELECTRODIALYTIC REMEDIATION

Célia Ferreira a,b, Lisbeth Ottosen b, Alexandra Ribeiro c, aCERNAS, Escola Superior Agrária, 3040-316 Coimbra, Portugal; bDepartment of Civil Engineering, Technical University of Denmark, DK-2800 Lyngby, Denmark; cDep. de Ciências e Engenharia do Ambiente, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus de Caparica, 2829-516 Caparica, Portugal. E-mail: [email protected] In the current work electrodialytic remediation (EDR) was applied to remove heavy metals from municipal solid waste fly ash, a hazardous waste collected during flue gas treatment. According to the concept of sustainable development fly ash residues should be reused or recycled as much as possible. However, the presence in fly ash of heavy metals is one of the major environmental constrains regarding its reuse, since potential leaching might result in groundwater and soil contamination [1].

The main objective of the present work is to improve EDR efficiencies by pre-washing the fly ash to remove soluble salts. Another objective is to assess the impact of EDR in reducing the environmental risk posed by fly ash.

Three different washed samples were prepared by introducing different amounts of flyash, water and nitric acid in plastic bottles and shaking for 18 hours. Analysis of the washing liquid shows that the pre-treatment is successful in removing major constituents, such as K, Na and Ca. However, in some cases it also removes high amounts of lead (as high as 59%), and some zinc. To avoid treatment of the liquid phase (for instance to remove metals by co-precipitation) the preliminary treatment in which the release of metals was minimum was selected.

The washed fly ash was then further treated by EDR. During EDR an electric field is applied to the waste, forcing-out soluble contaminants through a set of selective ion-exchange membranes (the fundamentals of the technique have been described in detail by Ottosen et al. [2]). The laboratory cell used consists of a Plexiglas cylinder (4 cm in diameter) divided transversely into 5 compartments separated by ion-exchange membranes. Two inert electrodes (diameter 3 mm) were placed at either end of the cell. Fly ash was introduced in the central chamber together with sodium gluconate and distilled water. NaNO3 (0.01M) was used as electrolyte in remaining chambers. A constant current of 38mA was applied for 14 days, using gluconate as a solubilisation enhancement agent. Conductivity, voltage drop and pH were monitored and electrolyte samples were collected every 4 days to evaluate metal release over time. Electrolytes’ pH was adjusted to 2 on the cathode side and kept above 1 on the anode side. At the end of the experiment the cell was dismantled and electrolytes and sample were collected. Membranes and electrodes were put in nitric acid (5M) overnight and the solutions analyzed for the interest heavy metals. The solid fraction of the sample (after filtration) was dried at 105ºC and analyzed for total heavy metal content.

The amount of metal deposited on the membranes was used as an indicator of membrane fouling: less than 3% were found at the membranes, as opposed to a similar experiment without preliminary washing [3], where this parameter reached 45%. Another indicator on remediation efficiency is the amount of metal present in the solution inside central compartment. In the experience without preliminary washing this parameter was 48% while with pre-washing it was less than 1%. This indicates that

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the preliminary treatment is effective in reducing membrane-fouling and in increasing metal removal. The preliminary washing also means that less energy was wasted in the transport of soluble salts.

To assess the possible impact of EDR in reducing the environmental risk posed by fly ash it is necessary to evaluate how metals are bond to the ash: more important than the total amount left in the ash after treament is the amount of the easily soluble fraction, since this last fraction poses the highest environmental risk.

To evaluate this parameter a sequential extraction was performed to the sample before and after EDR. The procedure is an adaptation of the schemes presented in [4-5] and allows the identification of 6 different fractions, which were further grouped in 3 main categories: “readily soluble”, “strongly bonded” and “residual”. It was seen that after EDR metals in the fly ash are mainly found in the strongly bonded and residual phases, thus indicating that the treatment has been successful in reducing the environmental risk posed by this waste.

The treatment by EDR aims at removing the readily soluble fraction, which causes the major impacts on the environment due to its leaching potential. EDR does not intend to remove the more strongly bound fractions since they are not of environmental concern for the current available disposal/reuse options. The efficiency of the remediation was therefore calculated as the percentage of metal from the easily soluble fraction which was removed during treatment. Results show that almost all Zn (88%) and Cd (92%) present in the easily soluble forms were extracted, indicating that treatment was successful for these metals. For lead and copper the results are 31% and 13% respectively. A comparison with a similar experiment [3] without preliminary washing shows that efficiencies, while similar for lead, were higher for the other metals, even though remediation time was 1/3 (14 days instead of 40).

The main conclusions of this work are firstly, that the preliminary treatment is successful in reducing fouling of the ion-exchange membranes during EDR of fly ash and increases performance and, secondly, that metals in the EDR-treated fly ash are mainly found in the strongly bonded and residual phases, thus indicating that the treatment has been successful in reducing the environmental risk posed by fly ash. [1] Ferreira, C., Ribeiro, A., Ottosen, L. Possible applications for municipal solid waste fly ash. J Hazard Mater, 2003, B96, 201-216. [1] Ottosen, L.M., Hansen, H.K., Laursen, S., Villumsen, A. Electrodialytic remediation of soil polluted with copper from wood preservation industry. Environ. Sci. Technol, 1997, 31, 1711-1715. [3] Ferreira, C., Ribeiro, A., Ottosen, L. Treatment of MSW fly ashes using the electrodialytic remediation technique, in: Brebbia, C.A, Kungolos, S., Popov, V., Itoh, H. (Eds.), Waste Management and the Environment II. Wit Press, 2004, UK. [4] Wunsch, P., Greilinger, C., Bieniek, D., Kettrup, A. Investigation of the binding of heavy-metals in thermally treated residues from waste incineration. Chemosphere, 1996, 32, 2211-2218. [5] VanHerck, P., VanderBruggen, B., Vogels, G., Vandecasteele, C.,. Application of computer modelling to predict the leaching behavior of heavy metals from MSWI fly ash and comparison with a sequential extraction method. Waste Manag, 2000, 20, 203-210.

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AN ENHANCED ELECTROKINETIC REMEDIATION FOR LEAD REMOVAL FROM SOILS POLLUTED FROM A ZINC

PRODUCTION PLANT Ahmet Altina, Mustafa Degirmencib

aDept. of Environmental Eng., Z. Karaelmas University, 67100-Zonguldak-TURKEY; bDept. of Environmental Engineering, Cumhuriyet University, 58140-Sivas-TURKEY E-mail: [email protected] ABSTRACT The effectiveness of the electrokinetic remediation enhanced with acetic acid (AcH) in sandy soils polluted from a zinc production plant was investigated. Best removal efficiencies were obtained by using 3 molar AcH in the cathode chamber and applying 20 volt constant potential. For these conditions, lead (II) removal efficiencies for sandy soils were varied between 65% and 85% up to 0.6 of normalized distance from anode.

Key Words: Electrokinetic remediation, Sandy soil, Lead (II), Zinc production plant INTRODUCTION During the electrokinetic remediation experiments, numerous electrochemical reactions and soil-contaminant interactions can take place, simultaneously [1]. Especially, the precipitation reactions closed to cathode area affect the effectiveness of the remediation, negatively. These reactions can be hindered by using purging solutions (AcH, citric acid, HCl etc.) [2]. The aim of this study is to investigate the treatability of lead (II) from a sandy soil, polluted with solid/gas emissions of a zinc production plant, by electrokinetic remediation process. In order to increase of the removal efficiency, the different concentrations of acetic acid (AcH) were applied as purging solution into the cathode chamber. MATERIALS AND METHODS In this study, samples taken from near by the zinc production plant in Kayseri City (Turkey) were used. For the determination of mineralogical properties of the samples, XRD whole-rock analyses were conducted. According to the results, the soil samples contain significant amounts of quartz (45%) and feldspar (47%) minerals, and contain low amounts of clinoptilolite (6%) and simectite (2%) minerals. The samples can be classified as sandy soil, evaluating grain size distribution of the sample. The lead sorption capacity and the average lead concentration of the samples are 4.7 meq/100g.soil and 2650 mg/L, respectively. Electrokinetic remediation apparatus, adapted from [3], is consisted of an extraction cell, fluid-gas volume measurement devices, a DC power supply and a multimeter. In our experimental works, the anode and the cathode compartments were filled with distilled water and AcH (0.5 and 3.0 M) as purging solution, respectively. The remediation experiments were run under a constant potential (7.5 and 10 volt) during the treatment time of 272 hour. At the end of the each test, the soil samples sliced into six sections, and the values of pH and lead (II) concentration were measured in each slice. RESULTS AND DISCUSSION Puppala et al. [2] determined that pH value less than 6 would be sufficient to dissolve and remove the lead (II) in the soil and aid in lead (II) transport to cathode. Virkutyte et al. [4] also reported that precipitation reactions could be minimized at pH value less

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than 4.5. As seen in Fig.1a, it is possible to reach these pH values by using the purging solutions. The best removal efficiencies were obtained at the test conditions using 3 M AcH and by applying 20 volt constant potential (Fig.1b). In these test conditions, the lead (II) removal efficiencies were varied between 65 and 85% up to 0.6 of normalized distance. Similarly, Sah and Chen [5] pointed out that this efficiency for sandy soil was 70% up to 0.7 of normalized distance at the end of seventh day by using 0.1 M HCl as purging solution. In another study, Vengris et al. [6] also obtained 70% lead (II) removal up to 0.5 of normalized distance at 220th hours. Another result shown in Fig.1b reveals that the efficiencies increase with the increment of applied current. However, it is also taken into consideration by applicants that the energy expenditure of the process increases proportionally for high voltages [7].

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a) b)

Fig.1. The pH (a) and lead (II) (b) profiles for different test conditions [8]. CONCLUSION Conclusions derived from experimental studies are summarized as follows: • In order to removal lead (II) from sandy soils, electrokinetic remediation process

enhanced with AcH can be used effectively. • The precipitation reactions taken place closed to cathode area may be hindered by

using 0.5 M AcH. However, lead (II) removal efficiencies of the tests using 3 M AcH are better than that using 0.5 M.

• The energy consumption of the process increases significantly, whereas applying high potential affects the effectiveness of the remediation, positively.

[1] Chung, H.I., Kang, B.H., 1999. Lead Removal from Contaminated Marine Clay by Electrokinetic

Soil Decontamination, Engineering Geology, 53, 139-150. [2] Puppala, S.K., Alshawabkeh, A.N., Acar, Y.B., Gale, R.J., Bricka, M., 1997. Enhanced

Electrokinetic Remediation of High Sorption Capacity Soil, J. of Hazardous Materials, 55, 203-220. [3] Hsu, C.N., 1997. Electrokinetic Remediation of Heavy Metal Contaminated Soils, PhD Dissertation,

Texas A & M University, Texas, 285 p. [4] Virkutyte, J., Sillanpaa, M., Latostenmaa, P., 2002. Elektrokinetic Soil Remediation: Critical

Overview, The Science of the Total Environment, 289, 97-121. [5] Sah, J.G., Chen, J.Y., 1998. Study of the Electrokinetic Process on Cd and Pb Spiked Soils, J. of

Hazardous Materials, 58, 301-315. [6] Vengris, T., Binkiene, R., Sveikauskaite, A., 2001. Electrokinetic Remediation of Lead, Zinc and

Cadmium Contaminated Soil, J. of Chemical Technology and Biotechnology, 76, 1165-1170. [7] Azzam, R., Oey, W., 2001. The Utilization of Electrokinetics in Geotechnical and Environmental

Engineering, Transport in Porous Media, 42, 293-314. [8] Altin, A., Altin, S., Atmaca, E., Degirmenci, M., (2004), Lead (II) Removal from Natural Sandy

Soils By Enhanced Electrokinetic Remediation, B. of Environmental Contamination and Toxicology 73(3), 551-560.

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ELECTROLYTE CONDITIONING FOR ELECTROKINETIC REMEDIAITON OF ARSENIC FROM MINE TAILING

Do-Hyung Kima, Byung-Gon Ryua, Sung-Woo Parka, Jung-Seok Yang,b, Kitae Baeka

aDepartment of Environmental Engineering, Kumoh National Institute of Technology, 1 Yangho-dong, Gumi, Gyeongbuk 730-701, Republic of Korea bKIST Gangneung Institute, Gangneung Techno Valley, 290 Daejeon-dong, Gangneung, Gangwon-do, 210-340, Republic of Korea E-mail: [email protected] 1. Introduction In Korea, mine tailing has been a serious environmental issue because of high concentration of heavy metals including arsenic, cadmium, copper, zinc and nickel. The site used in this study was iron mining area located in the south-eastern part of Seoul, Korea, approximately 450 km. The iron mine has been exploited and yielded manly iron from 1906 to 1993 and partially serpentine rock from 1966 till quite recently. The site will be a hilly district on a plain with a resident apartment complex [1]. Arsenic concentration of the mine tailing was 83 mg/kg. In Korea, the arsenic regulation level is 6 mg/kg in soil. Sequential soil washing with strong alkaline and acid technology has been investigated to remove arsenic from the mine tailing, however, the residual concentration of arsenic was higher than 6 mg/kg [1,2].

Arsenic is present in the environment in two common oxidized forms, arsenite and arsenate. Arsenite is known to be more toxic and 25-60 times more mobile than arsenate. Arsenite and arsenate are oxyanion, they have negative charge in wide pH range. Electromigration and electroosmotic flow(EOF) are major removal mechanisms in electrokinetic removal of arsenic. The direction of electromigration of arsenic is from cathode to anode, however, that for EOF can be changed by zeta potential of mine tailing surface.

In this study, the feasibility of electrolyte conditioning on electrokinetic removal of arsenic from mine tailing was investigated in the laboratory scale.

2. Materials and Methods The mine tailing used in this study was sampled from the site described previously. The mine tailing was dried, sieved using mesh 10 and mine tailing with < 2.0 mm was used in electrokinetic experiments. Table 1 shows experimental conditions. To enhance extraction of arsenic from mine tailing, anolyte or catholyte was conditioned by circulating alkaline or acid solution. The solution was changed to fresh electrolyte everyday. Electrokinetic treatment was executed at a constant current density of 2 mA/cm2. After 28 days, the mine tailing was sliced into 10 sections, and arsenic concentration, pH and water content of each section were analysed. Arsenic concentration was analyzed by Korean standard test method for soil: 10 g of mine tailing was mixed 50 ml of 1.0 N HCl, and agitated during 1 hour. The supernatant was analyzed using ICP (Varian 3700).

3. Results and Discussion Figure 1 shows pH distribution of mine tailing after experiments. Except Exp. 3, pH of mine tailing was alkaline conditions. In Exp. 3, the pH of mine tailing was 8.5, which value was similar to initial pH of mine tailing. In Exp. 1, pH of mine tailing increased

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compared to initial pH (8.47) because the concentration of calcium oxide contained in the mine tailing was high and calcium oxide was dissolved by acid front. This result means that the mine tailing has large buffering capacity to acid. Generally, extraction of arsenic from soil was enhanced by alkaline condition. We can expect high removal efficiency of arsenic. However, mine tailing used in this study contains a lot of CaO (57 wt %). The material caused high pH of mine tailing, and the tailing has high buffering capacity against acidic circulation.

Figure 2 shows arsenic distribution in mine tailing after experiment. Overall removal efficiency of arsenic was 59%, 44%, 37% and 37% for Exp. 1, Exp. 2, Exp. 3 and Exp. 4, respectively. In Exp. 1 (electrolyte only) and Exp. 3(circulation with acid), arsenic concentration in anode region was higher than middle section and cathode region. Especially, direction of electroosmotic flow was changed toward anode from cathode after 5 days operation in Exp. 3. Anolyte circulating with alkaline solution was not effective (Exp. 2 and Exp. 4). On the contrary higher concentration of alkaline solution decreased the removal of arsenic. In Exp. 2 and Exp. 4, arsenic concentration in cathode region was slightly higher than anode region because high pH caused more electro-osmotic flow. Anolyte circulation with acidic solution was enhanced arsenic removal compared to control experiment.

Table 1. Composition of electrolyte for electrokinetic experiments. Circulating solution for Anolyte Circulating solution for Catholyte

Exp. 1 MgSO4 1.0 M

Exp. 2 NaOH 0.5 M

Exp. 3 MgSO4 1.0 M HNO3 0.1 M

Exp. 4 NaOH 0.1 M

[1] I. Ko, Y.-Y. Chang, C.-H. Lee, K.-W. Kim, Asessement of pilot-scale acid washing of soil contaminated with As, Zn and Ni using BCR three-step sequential extraction, J. Hazad. Mater. A127 (2005) 1-13 [2] M. Jang, J.S. Hwang, S.I. Choi, J.K. Park, Remediation of arsenic-contaminated s oils and washing effluent, Chemosphere 60 (2005) 344-354.

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0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.07

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Fig. 1. pH distribution in soil section

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ANOLYTE CONDITIONING-ENHANCED ELECTROKINETIC REMEDIATION OF FLUORINE-CONTAMINATED SOIL

Do-Hyung Kima, Kitae Baeka, Sung-Hwan Kob

aDepartment of Environmental Engineering, Kumoh National Institute of Technology, 1 Yangho-dong, Gumi, Kyeongbuk 730-701, Republic of Korea bEcophile Inc., Yongin, Kyunggi, Republic of Korea E-mail: [email protected] 1. Introduction Fluorine is accumulated by drinking water in the human body. Other environmental problem is a long term accumulation of fluorine in the soil through major industrial and agricultural sources[1]. It has been reported that fluorine caused fluorosis to damage a bone and nerve system when it intake a long period. Therefore, it needs to restore the fluorine-contaminated soil and ground water. In this study, feasibility on electrokinetic remediation of fluorine-contaminated soil was investigated by conditioning anolyte with alkaline solution and in the points of removal efficiency and power consumption.

2. Materials and methods

Initial concentration of fluorine in soil sample was 414 mg/kg. Initial pH and water content of soil were 8.91 and 15%, respectively. The soil was sampled from contaminated area, dried, and sieved to pass a 10 mesh screen and soil with < 2.0 mm was used for electrokinetic experiments. The experimental apparatus consisted of four major compartments: the soil cell (4 x 4 x 20) cm3, the electrode compartments (4 x 4 x 1) cm3, the electrolyte solution reservoirs, and the power supply. It is important to control pH for the electrokinetic remediation. So we used sodium hydroxide as electrolyte to control pH in the anode compartments. Electrolyte solution was circulated in anode electrode compartments using peristaltic pump to control pH of electrolyte, and changed with fresh NaOH solution everyday. The electrical current density was 2-5 mA/cm2. Experimental conditions were summarized in Table 1.

Table 1. Experimental Conditions for Electrokinetic Remediation Exp. No. Anolyte Current density (mA/cm2) Duration(day)

Exp. 1 NaOH (0.1 M) 2 14

Exp. 2 NaOH (0.1 M) 5 14

Exp. 3 NaOH (0.5 M) 2 14

Exp. 4 NaOH (0.5 M) 3 14

The experiments of Exp. 1 and Exp. 2 were carried out to evaluate the effect of current density on the removal of fluorine. The experiments of Exp. 1 and Exp. 3 were executed to study the effect of anolyte concentration on removal of fluorine. Removal efficiency of fluorine increased as sodium hydroxide concentration and current density increased. After 14 days, the soil was sliced into 10 sections. Fluorine of soil sample from each slice was extracted using Korean Standard Test Method, and the extractants was reacted with zirconium, and the complex were analyzed using UV/VIS spectrophoto-meter(HS3300, Humas, Korea).

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3. Results and Discussion Figure 1 shows pH distribution of soil sections after experiments. pH of soil sections was ranged from 11 to 12.5 and even anode section was strong alkaline conditions. As concentration of circulating solution(NaOH) increased, the pH in soil section increased compared to lower concentration of the solution. It is well known that the extraction of fluorine from soil was enhanced by alkaline condition[2, 3] because hydroxide(OH-) could be exchanged into fluoride(F-). Figure 2 shows fluorine distribution in soil sections after experiment. Average removal efficiency of fluorine was 51.8%, 67.1%, 64.4% and 75.6% for Exp. 1, Exp. 2, Exp. 3 and Exp. 4, respectively. Electromigration and electroosmosis are major removal mechanisms in electrokinetic removal of fluorine. Electroosmotic flow is enhanced by alkaline condition of soil [4, 5]. Fluorine concentration in soil was homogeneously distributed compared to other electrokinetic experiments because enhanced osmotic flow moved fluoride from anode to cathode and fluoride was transferred from cathode to anode by electromigration.

4. Conclusions Even though anolyte circulation with alkaline solution caused increase of soil pH upto 12.0, this high soil pH enhanced fluoride desorption from soil. Anolyte circulation with alkaline solution in electrokinetic remediation was one of most effective for fluorine removal.

Fig. 1. pH distribution in the soil sections

Normalized distance from anode0.0 0.2 0.4 0.6 0.8 1.0

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Acknowledgement This research was supported by a grant from Korea Foundation of Science and Technology via National Research Laboratory Program. [1] M. A. Elrashidi, W. L. Lindsay, Chemical equilibria of fluorine in soils: A Theoretical development, Soil Sci. 141 (1986) 274-280. [2] N. Costarramone, S. Tellier, B. Grano, D. Lecomte, M. Astruc, Effect of selected conditions on fluorine recovery from a soil, using electrokinetics, Environ. Technol. 21 (2000) 789-798. [3] Walter W. Wenzel, Winfried E. H. Blum, Fluorine speciation and mobility in F-contaminated soils, Soil Sci. 153 (1992) 357-364. [4] Andrew P. Shapiro, Roland F. Probstein, Removal of Contaminants from Saturated Clay by Electroosmosis, Environ. Sci. Technol. 27 (1993) 283-291. [5] Jihad T. Hamed, Ashish Bhadra, Influence of current density and pH on electrokinetic, J. Hazard.Mater. 55 (1997) 279-294.

Fig. 2. Fluorine distribution in the soil sections Normalized distance from anode

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ELECTROKINETIC REMEDIATION OF Ni AND Zn CONTAMINATED SOIL: CATHOLYTE CONDITIONING

Do-Hyung Kima, Hyun-Duck Choia, Min-Chul Shina, Chil-Sung Jeona, Kitae Baeka

a Department of Environmental Engineering, Kumoh National Institute of Technology, 1 Yangho-dong, Gumi, Gyeongbuk 730-701, Republic of Korea E-mail: [email protected] 1. Introdcution Several technologies including soil washing, solidification/stabilization and electrokinetic have been applied to clean-up metal-contaminated soils. Electrokinetic treatment is an innovative method to extract metal from contaminated soil[1]. In the case of multi-metal contamination, enhancement methods are devised for specific contaminants and conditions[1]. Common enhancement method is control of pH in soil section using circulation of anolyte or catholyte with strong acid, strong base or organic acid[1,2]. In this study, the feasibility of electrokinetic remediation on nickel and zinc-contaminated soil was investigated in the laboratory scale with field soil using catholyte conditioning with strong acid and pre-treatment of soil with acid.

2. Material and Methods The soil used in this study was contaminated by soot, which contains high concentration of Ni and Zn, in power plant. Initial concentration of Ni and Zn were 1,324 and 1,632 mg/kg, respectively. The soil was sampled in the field and sieved using mesh 10. Soil with < 2 mm was used in electrokinetic experiments. The experimental apparatus consisted of four principle compartments: the soil cell (4cm x 4cm x 20cm), the electrode compartments fitted with graphite carbon electrode (4 x 4 x 0.8 cm), the electrolyte solution reservoirs, and the power supply. Electrolyte solution was circulated in both electrode compartments using peristaltic pump to adjust pH of electrolyte, and the solution changed with fresh catholyte or anolyte everyday. The electrical gradient was 2 V/cm. Experimental conditions were summarized in Table 1.

3. Results and Discussion Fig. 1 shows the performance of electrokinetic remediation for the contaminated soil. Even though nickel and zinc were moved from anode to cathode section, the overall removal efficiency was less than 10%. The movement of zinc was faster than nickel. In Exp. 3, movement of zinc was more than other experiments because the catholyte pH was adjusted with acetate buffer solution. Soil washing technique was tested to evaluate the pH effect on removal of nickel and zinc from the soil. Except pH 1.0 solution, the removal of nickel and zinc from soil was negligible because the equilibrium pH was greater than pH 4.0. To decrease soil pH, the soil sample was pre-treated with nitric acid (0.1 M) and catholyte was circulated with various concentration of nitric acid in Exp 5 – Exp.8.

Overall removal efficiencies of zinc were 23%, 33%, 28%, and 41% for Exp. 5, Exp. 6, Exp. 7, and Exp. 8, respectively. For Ni, removal efficiencies were 20%, 31%, 24%, and 40% for Exp. 5, Exp. 6, Exp. 7, and Exp. 8, respectively. The removal of nickel and zinc in Exp. 5 increased dramatically compared to Exp. 1. This result means that pre-treatment of soil sample with acidic solution enhanced the removal of nickel and zinc. Theoretically, higher concentration of acid for circulating catholyte makes more acidic condition in soil, and then the removal of nickel and zinc increased. However, low pH of soil changes the net zeta

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potential of soil from negative to positive due to sorption of hydrogen ion onto soil surface. In the soil with positive surface charge, the direction of electroosmotic flow changes from cathode to anode. Lower pH of soil enhances the desorption of nickel and zinc from soil to pore fluid. However the overall removal of metal ion was not enhanced significantly because the direction of electromigration and electroosmotic flow was opposite. Acidic pre-treatment of soil and catholyte conditioning with acidic solution enhance the performance of electrokinetic remediation of nickel and zinc, however there is optimum concentration of acidic solution for catholyte conditioning.

Fig. 1. Distribution of Zn and Ni after application of electrokinetic remediation Table 1. Experimental conditions for electrokinetic remediation

Exp. No. Anolyte Catholyte

Pre-treatment

of soil

Exp. 1 MgSO4 (0.05 M)

Exp. 2 Acetic acid (0.1 M) + MgSO4 (0.05 M)

Exp. 3 MgSO4 (0.05 M) Acetic acid (0.1 M) + Sodium Acetate (0.1 M) at pH 4.0

Exp. 4 EDTA (0.1M) + MgSO4 (0.05M)

Exp. 5 MgSO4 (0.1 M) HNO3 (0.1 M)

Exp. 6 MgSO4 (0.1 M) HNO3 (0.1M) HNO3 (0.1 M)



[1] D.M. Zhou, C.-F. Deng, L.Cang, A.K. Alshawabkeh, Chemosphere 61(4), 519-527 (2006) [2] H.K. Hansen, A. Rojo, L.M. Ottosen, J. Hazard. Mater. B117, 179-183 (2005)

Normalized distance from anode0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

C/C

0, N

iExp-01Exp-02Exp-03Exp-04


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

C/C

0, Zn

Exp-01Exp-02Exp-03Exp-04


C/C

0, Z

n

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6Exp-05Exp-06Exp-07Exp-08


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6Exp.-05Exp.-06Exp.-07Exp.-08

C/C

0, N

i

152


STRAW ASH – ELECTRODIALYTIC REMOVAL OF CD IN A PILOT SCALE

A. T. Limaa *; Ottosen, L.M.b; Ribeiro, A.B.a; H.K. Hansenc

aDepartamento de Ciências e Engenharia do Ambiente, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal; bDepartment of Civil Engineering, Brovej, Building 118, DTU, DK-2800 Lyngby, Denmark; c Departamento de Procesos Químicos, Biotecnológicos y Ambientales, Universidad Técnica Federico Santa Maria, Casilla 110-V, Avenida España 1680, Valparaíso, Chile E-mail: [email protected] Straw is a valuable raw material in a growing industry of combustion of biomass from agricultural fields, especially in agricultural countries. Biomass combustion is an alternative source of energy with growing potentiality. Danish regulations define the application of fly ashes from the combustion of straw to agricultural fields up to 5 mg Cd kg-1 in 0.5 ton/5 yrs [4, 7]. Cadmium is a heavy metal that comes from both natural and man-made sources. Phosphate fertilizer and sludge applications in agriculture may be the contamination source of straw, through indirect adsorption (adapted from [2]). Most often Cd concentration exceeds regulations in straw ashes. The electrodialytic process (EP) is a remediation technique, with verified success, since it was first described for heavy metal contaminated soil [3, 5, 6]. The process is based on the principle of electrodialysis, i.e., it combines the electric field effect with ionic-exchange membranes. Basically, the electric field transports electrically charged ions to the electrodes and the ion-exchange membranes select which ions pass from contaminated media to the electrode compartments.

Figure 1 – Ultimate target for the remediation of straw ashes

Reuse as fertilizer

Straw Ash

Water

Residual Solid fraction: • Low Cd content

Liquid fraction: • High Cd content

Pre-wash Solution exceeding: • High KCl content

+ – Electrodialytic Treatment

Agricultural fields

Treatment to reduce Cd

Figure 1 schematizes the ultimate goal of the electrodialytic method for straw ash and its sustainable ideal. The contaminated fly ash is combined with an assisting solution and EP is carried out. The outputs of the process would be a solid fraction with low

153

heavy metal content and a liquid fraction containing the heavy metals. At the end both fractions could be reintroduced in the market. The straw ash solid fraction is added directly to agricultural fields and the liquid fraction is used in the production of fertilizer (K is of interest here) after precipitation of Cd (Figure 1). The scale up of EP has been carried out before by Christensen et al., in a 2 m3 pilot plant for wood waste [1]. In the present study, the application of the EP to fly ashes from the combustion of straw in a medium size prototype scale was preformed. The migration of Cd was studied throughout the remediation time and removal rates were compared. Overall, straw ashes are quite suitable for the removal of Cd through electrodialytic remediation since Cd is readily desorbed. Experiments suggest an evaporable Cd fraction, which may be enhanced by the acidic conditions of the ash suspension at room temperature. The final straw ash achieved a low Cd content, though further adjustments need to be carried out in order to optimize Cd removal rate. EP ultimate target is to remove heavy metals from the central compartment into electrolyte compartments. Due to the continuous electrolyte flow into the central compartment, probably due to high concentrations of salts, Cd removal may have been slowed down. The straw ash after electrodialytic remediation has a low pH (2), low Cd (6.8 mg Cd/kg) content and high K residue. Application to land should be moderate, with special emphasis on the application to neutral/alkaline soils. To achieve the sustainability principle Cd concentration in the solutions should be lowered for further reuse in fertilizers. This could be accomplished through alkalinisation of the solutions. Bottom line, Figure 1 represents the ultimate resource for the remediation of straw ashes. Once Cd is removed from the central compartment/ash and isolated in electrolyte units, the ashes may be considered isolated from the metal. These ashes are of great value in agricultural fields, since its potassium content is high (probably in the form of KCl). The residual solutions from EP might be introduced in the original industry, in this case fertilizers industry. The liquid fraction from pre-wash procedure may also be reused in fertilizer industry. [1] Christensen IV, Pedersen AJ, Ottosen LM, Ribeiro AB (2006). Electrodialytic remediation of CCA-treated waste wood in a 2 m3 pilot plant. Science of the Total Environment 364:45-54. [2] European Commission DG ENV E3 (2002). Heavy Metals in Waste – Final Report, Project ENV.E.3/ETU/2000/0058. [3] Hansen HK, Ottosen LM, Kliem BK, Villumsen A (1997). Electrokinetic Remediation of Soils Polluted with Cu, Cr, Hg, Pb and Zn. J. Chem. Tech. Biotech, 70:67-73. [4] Miljø-og Energiministeriet: Bekendtgørelse om anvendelse af aske fra forgasning og forbrænding af biomasse og biomasseaffald til jordbrugsformål. BEK no. 39, 20/02/2000 (in Danish). [5] Ottosen LM, Hansen HK (1992). Electrokinetic cleaning of heavy metals polluted soil. Internal Report,Fysisk-Kemisk Institut for Geologi og Geoteknik, Technical University of Denmark, Denmark, 9pp. [6] Ottosen LM, Hansen HK, Laursen S, Villumsen A (1997). Electrodialytic Remediation of Soil Polluted with Copper from Wood Preservation Industry, Environmental Science & Technology, 31:1711-1715 [7] Pedersen AJ (2003). Characterization and electrodialytic treatment of wood combustion fly ash for the removal of cadmium. Biomass Bioenergy 25:447–58.

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ELECTROKINETIC REMEDIATION OF METAL AND SURFACTANT FROM SEWAGE SLUDGE

Violetta Ferria, Sergio Ferroa, Claudio Anzaloneb, Achille De Battistia

a Chemistry Department, Ferrara University, via L. Borsari 46, 44100 Ferrara, Italy b HERA SpA, Divisione Reti R&D - via Balzella 24, 47100 Forlì, Italy E-mail: [email protected] Introduction The disposal of sewage sludge from urban wastewater treatment plants is a growing problem worldwide. The European Community1 has developed the draft of “Working document on sludge” with the aim to update the regulatory system for the (re)use of sewage sludge. In Italy, sewage sludge could be disposed on agricultural lands but, in last years, this use has been limited by Italian legislation to avoid the contamination by and the accumulation of both heavy metals and organic compounds in the soils. Analogous regional regulations have decreased the maximum attainable limit for these pollutants. In order to increase the recycling of sludge on agricultural lands, thus avoiding their accumulation, we need a powerful treatment as electroremediation2. The present work reports on a laboratory investigation on the use of an electrokinetic method for the removal of anionic surfactants like linear alkylbenzenesulphonate (LAS) and heavy metals from wastewater sludge. Experimental section The sewage sludge was obtained from the HERA urban wastewater treatment plants located in Emilia Romagna. The basic cell for electrokinetic sludge remediation is shown in Fig. 1. The experimental apparatus consisted of the following parts: a sludge bed, two electrode compartments and a power supply. Each end of the sludge bed was equipped with holes (diameter: 1mm) and a paper membrane (2) to enhance uniform electro-osmotic flow. A titanium plate cathode (3) and a titanium coated platinum anode (1) were used. To find the optimal operating conditions, variable current intensities for different times were applied. To gain information about the process, pH, potential, conductivity and temperature were measured before and after each treatment, in both electrolyte compartments. After treatment, the sludge was dried and analysed to determine the concentration of heavy metals, by atomic absorption spectroscopy, and organic fraction, by extraction and NMR analysis.

3 2 1

1 3 2

In a second experimental session, we focused our attention on the possible removal of surfactants. In the various experiments, current densities of 2, 3, 4 and 5 mA/cm2 have been applied to the electrokinetic cell for 8, 16, 24 and 48 hours, respectively.

155

Table 1 Table 2

1 concentration of metals before treatment, 2 cathode side, 3 anode side Experimental conditions: test 3 - time 3 h, current density 4 mA/cm2; test 4 - time 8 h, current density 2.4 mA/cm2; test 6 - time 16 h, current density 2.4 mA/cm2; test 7 - time 48 h, current density 4 mA/cm2.

Removal efficiencies (%)

[M]1

(mg/ Kg) Test 3 Test 4 Test 6 Test 72 Test 73

As 19 -5% -21% -21% -64.9% -47.6%Cd 4.03 -% -8% -3% -10.2% 16.7%Co 12 -8% -23% -8% -71.9% -78.4%total Cr 88 -5% -20% -19% -36.3% -30.2%

Cu 563 - -10% -18% -40.4% -21.1%Ni 61 -13% -25% -25% -56.7% -54.1%Pb 139 12% -12% -16% -44.5% -13.0%V 70 -6% -17% -13% -25.4% -34.9%Zn 1147 -1% -3% -14% -27.7% -21.0%Fe 14000 -5% -14% -12% -5.1% -44.1%Mn 387 -8% -16% -14% 15.3% -99.4%

t: time treatment, j: current density

Test t (h)

j (mA/cm2)

LAS Removal efficiencies

(%) 13 24 3 17,3 14 24 4 18,0 15 24 5 19,7 16 24 6 43,2 17 16 3 27,3 18 16 4 28,8 19 16 5 28,3 20 16 6 22,2 21 8 3 22,4 22 8 4 41,7 23 8 5 31,9 24 8 6 24,7 25 48 3 29,1 26 48 4 22,6 27 48 5 18,7 28 48 6 31,2

Results and discussion The concentration of heavy metals in the sludge provided by HERA was below the limit set by the Italian legislation; however, it is interesting to observe that all metal contents could be reduced by the electrokinetic treatment. Values collected in table 1 show that removal efficiencies increase both by prolonging the application time and raising the current density. Also the concentration of surfactants in the sludge was below the limit set by the Italian legislation but, in consideration of their widespread use (household detergents, personal care), their increasing concentration could become a problem in the near future. Looking at the related experimental session, good results were obtained, i.e. LAS removal efficiencies between 18% and 43%. No substantial gain in removal efficiency could be obtained by prolonging the application time to more than 16 hour. The lack of a clear trend for data in table 2 could be due to problems in sample homogeneity and analytical determinations; therefore, the above data must be taken as preliminary results and inspected cautiously. Future work will be focused on scale-up of the electrokinetic process optimization of parameters for increasing the LAS removal efficiency optimization of LAS extraction procedure and their quantification by NMR.

This work was financially supported by HERA Group [1] Working document on sludge, 3rd draft 2000 [2] a) M.T. Ricart, H.K. Hansen, C. Cameselle, J.M. Lema, Sep. Sci. Technol. 2005, 39(15), 3679-3689; b) M. Elektorowicz, S. Habibi, Can. J. Civ. Eng. 2005, 32, 164-169; c) S.O. Kim, S.H. Moon, K.W. Kim, S.T. Yun, Wat. Res. 2002, 36, 4765-4774; d) G.J. Zagury, Y. Dartiguenave, J.C. Setier, J. Envi. Eng. 1999, 972-978; e) M.R. Jakobsen, J. Fritt-Rasmussen, S. Nielsen, L.M. Ottosen, J. Haz. Mat. 2004, 106, 127-132; f) J. Virkutyte, E. van Hullebusch, M. Sillanpa, P. Lens, Envi. Poll. 2005, 138, 517-528.

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DIALYTIC AND ELECTRODIALYTIC REMOVAL OF HEAVY METALS FROM MSW FLY ASH: EXPERIMENTAL AND

MODELING A. T. Limaa*, A. B. Ribeiroa, J. M. Rodríguez-Marotob, A. Varela-Castroc, L. M. Ottosend

aDepartment of Sciences and Environmental Engineering, Faculty of Sciences and Technology, New University of Lisbon, 2829-516 Caparica, Portugal; bDepartment of Chemical Engineering, University of Málaga, Campus de Teatinos, 29071-Málaga, Spain; c National Agricultural Station, Soil Science Department, Av. República, 2784-505 Oeiras, Portugal; d Department of Civil Engineering, Brovej, Building 118, Technical University of Denmark E-mail: [email protected]

Fly ash from municipal solid waste incinerators (MSWI) are considered hazardous waste, being their high concentration of heavy metals a major problem. In Portugal, MSWI fly ash are expected to increase over time which poses a growing concern about the waste management issue they represent. Various ways of valorizing them have been reported. The electrodialytic process (ED) removes heavy metals from fly ash, which eventually enables their further valorisation and the recovery of heavy metals for further reuse.

In the present work, the effect of applying a direct current as the “cleaning agent” for the heavy metals presented MSWI fly ash was investigated. Focus was given to a comparison between performances of dialytic vs. electrodialytic experiments, respectively with ion-exchange membranes as the main driving forces for gradient concentration of heavy metals, and electrodialytic experiments, in which an electric field was applied in order to accelerate heavy metal removal from the central cell compartment. The purpose was to differentiate the transport of heavy metals induced by chemical gradients and potential gradients.

Six electrodialytic experiments were carried out differing in several parameters, according to what is presented in Table 1. The time length of the experiments was maintained constant in 14 days. Two assisting agents were studied (0,25M ammonium citrate in 1,25% NH3 and distilled water. The experimental setup also varied according to Figure 1 (without and with stirring).

From the heavy metals studied, Cd, Cu and Pb, the best removal rates were obtained for Cd, with 0,25M ammonium citrate in 1,25% ammonia as the assisting agent, presenting the setup design no relevance. For Pb, the electrodialytic experiment with distilled water as saturation media achieved the best results.

A one-dimensional model was developed for simulating the electrodialytic and dialytic treatment of a saturated bed of MSW fly ash containing Cd, Pb, Cu and Al. The chemical equilibria precipitation –solubilization and the movement of individual ions Cd, Pb, Cu, etc and their complexes, Cd(OH)3

-, Pb(OH)3-, etc. was mathematically

modeled taking into account the diffusion transport resulting from their concentration gradients and from the electromigration of their ionic, simple and complex species during the operation.

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Table 1 – Experimental conditions

Exp. Setup design Assisting Agent Current

(mA) Anolyte L/S

1 A 0,25M Ammonium Citrate in 1,25% Ammonia

40 0,25M Ammonium Citrate in 1,25% Ammonia

1,66

2 A 0,25M Ammonium Citrate in 1,25% Ammonia


1,66

3 B Distilled Water 40 0,01M NaNO3 at pH=2 4 4 B Distilled Water 0 0,01M NaNO3 at pH=2 4 5 B 0,25M Ammonium

Citrate in 1,25% Ammonia


4

6 B 0,25M Ammonium Citrate in 1,25% Ammonia


4

Figure 1 – Setup design for the studied expeCAT – cation exchange membrane; I – anodIII – cathode compartment; A – unstirred ash;

riments. AN – anion exchange membrane; e compartment; II – central compartment; B – stirred ash suspension.

+ –fly ashes + assisting agent

L = 3 cm A

I II III

AN CAT

+ –L = 10 cm

fly ashes + assisting agent

Stirring device

I III II

AN CAT B

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ELECTROCHEMICAL RE-IMPREGNATION OF WOOD WITH COPPER

Iben V. Christensen, Lisbeth M. Ottosen, Simon R. Jensen; Morten B. Jacobsen Department of Civil Engineering, Building 118, Technical University of Denmark, 2800 Lyngby, Denmark E-mail: [email protected] Introduction

When wood in structures starts to decay, the only choices today are to surface treat the wood or to replace the damaged wood with new wood. Replacement is not an option in every case, e.g. in heritage buildings or in constructions where this action is very costly due to the placement of the wood in the structure. Surface treatment suffers from not offering a fast protection against the decay. Such treatment is based on diffusion of the wood preservative into the wood and this transport is often in the range of few mm per month and if the decay reaches deeper into the wood, this treatment is insufficient. Methods where holes are drilled in the wood and the wood preservative is supplied into these holes have been developed to protect the wood in depth, but still the diffusion rate is very limited and the decay is not efficiently stopped. Boron and/or copper based preservatives are most often used for surface treatment. In the present work it was investigated whether it is possible to increase the rate of Cu transport into the wood by applying an electric DC field compared to diffusion.

Materials and methods The experimental setup used is shown in Figure 1. The wood (cylindrical, length 10 cm, diameter 5 cm) was wrapped tight in plastic to avoid evaporation. At the anode side of the wood a supply compartment was placed containing Celcure AC800 which is a copper-amine preservative from Osmose. At the cathode side was placed a compartment with NaNO3 to ensure good electrical contact. The electrodes were placed in carbonate rich clay to prevent the acidic front in reaching the supply compartment and possible also the alkaline front in reaching the wood. The wood was chosen carefully so both sapwood and hard wood was present at almost equal volume. The wood was water saturated by soaking (water content > 28%).

Figure 1: Experimental setup

After the experiments the wood was cut into two halves in longitudinal direction. Chromazurol S was sprayed on one halve (a colour indicator showing Cu in blue) and

Nr. Description 1 Tube Pump 2 Beaker with wood preservative 3 Tubes for circulation 4 Anode 5 Anode compartment (clay) 6 Supply compartment 7 Wood 8 Collection compartment 9 Catode compartment (clay)

10 Catode 11 Beaker 12 Power supply

159

the other half was cut into 10 slices (that were further separated into hard wood, sap wood and a mixture of these) for chemical analysis. Five experiments were conducted with constant current. The experimental parameters varied were the applied current and the duration: (A) 0 mA, 22 days. (B) 1.5 mA, 29 days, (C) 2.5 mA, 29 days, (D) 3.5 mA, 9 days and (E) 2.5 mA, 16 days. In experiments (A) to (D) a 0.16% Celcure AC800 was supplied and in experiment (E) the concentration was increased to 3.2%.

Results and discussion Figure 2 shows the distribution of Cu in the wood after electrokinetic treatment (B-D) and in the reference experiment (A).

A C

B D

Figure 2: Experiments (A) to (D). Distribution of Cu in the wood after treatment (sapwood up, Hardwood down).

Compared to the reference experiment it is seen that the transport of Cu into the wood is significantly increased by the applied current in the three electrokinetic experiments. The visual distribution found with chromazurol (Figure 2) was confirmed with chemical analysis. The charge transfer in the eletrokinetic experiments was (B) 3800 C, (C) 6300 C and (D) 2700 C and this corresponds well to the depth of which Cu was transported into the wood.

Figure 3: Distribution of Cu in exp. (E).

By increasing the concentration of the supply solution from 0.16% to 3.2% most of the sapwood was impregnated during 16 days and Cu was measured in the first 4 cm in the hardwood. The Cu concentration was more than 3380 mg/kg in all sapwood and in exp. (C) the highest concentration measured in the first slice only was 1650 mg/kg.

It was clearly shown that re-impregnation can be improved by applying an electric field since Cu is distributed much faster into the wood. Due to these encouraging results optimisation of process parameters as well as development of electrode units are done.

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TRANSPORT OF BORON IN WOOD - AN ELECTROKINETIC ACCELERATED WOOD IMPREGNATION PROCESS

Iben V. Christensen*, Lisbeth M. Ottosen, Inge Rörig-dalsgaard BYG.DTU – department of Civil Engineering. Technical University of Denmark. Brovej building 118, DK-2800 Lyngby, Denmark. *Tel. (+45) 45 25 23 97, Fax: (+45) 45 88 32 82, [email protected] Introduction When wood already in construction is in need of re-impregnation, surface treatment with boron compounds are often used. Boron is a well known wood protection chemical, used in wood preservation world wide and generally accepted as a environmentally safe wood preservative [1]. When boron is used for surface treatment, the ingress of boron, and thereby impregnation of the total wood volume, is based on diffusion. Impregnation based on diffusion is a relatively slow process with ingress in the order of mm or few cm even several months after treatment ( Morrell et al. 1994). To speed up this process electrokinetic transport of boron is proposed.

Experimental section Samples of pine sap wood (26 mm radial,50 mm tangential, 50 mm longitudal) was cut from a board and water-saturated after vacuum treatment. The samples were then slowly dried out at room temperature to the desired moisture content (determined by weighing) and subsequently sealed by coating four of the six surfaces with plastic, leaving the end grain surfaces untouched. These surfaces were used in the experiments. The wood samples were then carefully wrapped in cling film and plastic bags until the electrokinetic experiments were initiated (1-2 weeks).

Boron, as boric-tartaric acid complexes, was applied (by brush) to one of the non-sealed surfaces. Electrodes in the form of iron mesh was attached to the radial surfaces after placing it in clay to obtain good contact between the electrodes and the wood and to ensure even distribution of the electric field on the surface. During the experiments the clay was covered with plastic (gaffa tape) to minimise evaporation.

Experiments were made with wood moisture contents of 30% and 35%. In all experiments the current was kept constant. Reference experiment was made for each series. Here the setup was identical to the electrokinetic experiments, but no electric field was applied. The duration was 1-3 days. After the experiments were ended, each sample was split in two and the one half was used for visual inspection of the ingress using curcumin reagent. The other half was used to determine the moisture content in the wood.

Results and discussion As seen in figure 1 it was possible to significantly increase the penetration of boron in wood with the use of an electric field. The red colour indicates the presence of boron. By decreasing the initial water content from 35% to 30% it was possible to apply twice the amount of boron, due to the drier wood surface.

For both series it seems obvious that the ingress of boron has been accelerated by the electric field. At 30% moisture content, the magnitude of the electric field was investigated and in the range tested here (0.25-1 mA) there is no significant dfference.

161

Figure 1: Boron penetration in wood.. Boron applied to (-) surface. Red colour indicate presence of boron.

Conclusion It is possible to accelerate the ingress of boron in wood by the use of an electric field, compared to ingress based on diffusion. The optimisation of the process is ongoing to investigate the limitations of the method (e.g. moisture content, boron concentration)

If the optimisation processs is successful, elelctrokietic accelerated boron ingress may prove to be a suitable alternative to existing methods for reimpregnation of wood. The metod seems especially suited for situations where replacement of wood should be avoided, e.g. cultural heritage buildings.

Acknowledgments This work was funded by the Danish Forest and Nature Agency (Skov- og Naturstyrelsen).

[1] Lloyd, J.D. (1997) International Status of Borate Preservative Systems. 2nd international conference on wood protection with diffusible preservatives. pp 45-54

[2] Morrell, J.J.; Forsyth, P.G.; Newbill, M.A. (1994) Distribution of biocides in Douglas-fir poles 42 months after application of groundline preservative systems. Forest Products Journal Vol. 44(6) pp.24-26

162


REMEDIATION OF A CHROMIUM (VI) CONTAMINATED SOIL BY ELECTRODIALYSIS

Ana M. Nieto Castilloa, Juan J. Sorianoa, Rafael A. García-Delgadoa

aInstituto Geológico y Minero de España (IGME) Dirección de Recursos Minerales y Geoambiente C/ Rios Rosas, 23. 28003-Madrid (SPAIN) E-mail: [email protected] A laboratory study has been carried out to determine the feasibility of in situ remediation of a clayey soil contaminated with chromium (VI) using electrodialysis in relation with its speciation in soil.

Remediation tests were carried out under constant voltage conditions for periods of 7-14 days and the evolution of applied current to the cell, pH and conductivity of the electrolytes was periodically recorded.

Speciation of chromium has been determined on soil samples before and after the remediation process using a standardized four step sequential extraction procedure (SEP). Results show that chromium is mobilized from the most labile phases (soluble/exchangeable/carbonatic) but also that changes in the total chromium distribution occur during the treatment and some of it is transferred to other soil phases which are more difficult to mobilize.

MATERIALS AND METHODS

A clayey soil has been prepared for use in the experiments by mixing fine sand and bentonite clay in the ratio 5:1 and has been characterized before being contaminated by mixing it with a solution of potassium dichromate for several days. The resulting soil presents a porosity of 0.4, a permeability of 6.60 10-7 cm/s and an initial Cr (VI) content of 4056 ± 95 mg/kg.

Treatment tests were carried out in an acrylic laboratory cell consisting of a 20 cm length central soil compartment of 230 cm3 and two 50 cm3 electrode compartments located at both ends of the column. Dimensionally stable titanium electrodes of 10 cm2 coated with mixed metal oxides were placed in the electrode compartments. 0.05M KNO3 electrolytes were recirculated through them from two 1 litre deposits using a peristaltic pump. The spent electrolytes were replaced after 7 days. Two commercial ion exchange membranes (Ionics Iberica CR67-HMR-402 (cationic) and AR204-SZRA-412 (anionic)) separated the anolyte and catholyte compartments from the soil. A 180 W programmable DC power supply was connected to the electrodes and a computer for data acquisition.

The study consisted of several runs under constant voltage conditions (15 - 30 V). Typical test duration was 7 or 14 days. Evolution of applied current to the cell as well as pH and conductivity of the electrolytes were periodically recorded. Electrolytes were also sampled for Cr content determination. At the end of the treatment period, soil cores of ca. 2g were taken at different positions in the cell for total Cr content and speciation analyses.

Speciation of chromium has been determined on soil samples before and after the remediation process using a standardized four step sequential extraction procedure [1]

163

using acetic acid, hydroxylamine, hydrogen peroxide and aqua regia solutions prepared from analytical grade reagents. Chemical analysis of digested soil samples, electrolytes and extracting solutions were carried by spectroscopy methods (AAS and ICP).

RESULTS

In every test, pH decreases at the anode and increases at the cathode as a consequence of the water electrolysis reactions that take place according to the expressions:

2 H2O – 4 e- → O2 (gas) + 4 H+ Eo = - 1.229 (anode) (1)

2 H2O + 2 e- → H2 (gas) + 2 OH- Eo = - 0.828 (cathode) (2)

where Eo is the Standard electrochemical reduction potential.

The magnitude of the variation depends on the applied current and can reach values below 2 and above 12 at the anode and cathode respectively. As the treatment proceeds, and the ions concentrate in the anolyte and catholyte, their conductivity increases and the colour of the anolyte turns yellowish because of the Cr (VI). Accumulation of chromium in the anode chamber shows that electromigration is the predominant driving force for the transport of ions. Removals of chromium of 27% at 15V and 57% at 30V have been achieved in one week treatments. Higher voltages yield higher initial removals rates and higher amounts of chromium at the cost of being more energy inefficient.

Initially most of the chromium in the soil is located in the most mobile fraction (81%) and similar amounts in the other 2 (7% and 10%) with little chromium in the residual fraction. As the electrodialysis treatment proceeds, the more labile phase (soluble + exchangeable + carbonatic) is depleted first and the amount of chromium in it decreases drastically to less than 7% as it is being removed from the soil into the anolyte solution. Results also show that changes in the total chromium distribution occur due to the treatment. Some of it is being transferred to the oxides and sulphides fractions which first increase and then decrease slowly.

ACKNOWLEDGEMENTS

This work is part of an R+D project co-financed by Spain’s Ministry of Environment.

[1] Rauret, G., Lopez-Sanchez, J.F., Sahuquillo, A., Rubio, R., Davidson, C., Ure, A. & Quevauviller, Ph. (1999). Improvement of the BCR three step sequential extraction procedure prior to the certification of new sediment and soil reference materials” J. Environ. Monit., 1, 57-61.

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A SIMPLE COMPUTER MODEL FOR THE ELECTRODIALYTIC REMEDIATION OF A CHROMIUM (VI) CONTAMINATED SOIL

Rafael A. García-Delgadoa ,Ana M. Nieto Castilloa, Juan J. Sorianoa aInstituto Geológico y Minero de España (IGME) Dirección de Recursos Minerales y Geoambiente C/ Rios Rosas, 23. 28003-Madrid (SPAIN) E-mail: [email protected] A one-dimensional computer model has been developed to simulate the electrodialytic treatment of a water saturated clayey soil containing chromium (VI). Model calibration has been carried out using previous laboratory tests. Additionally, the influence of different operation parameters and their effects on remediation time and energy use have been explored.

MATERIALS AND METHODS

A simple one dimensional computer model has been developed for simulating the electroremediation treatment. The model has been coded in FORTRAN. The main objective of this model is to supply an adequate qualitative and quantitative description of the behaviour of the pollutant-soil system and to become a useful predictive tool in improving the system’s performance by modifying the operation parameters.

In the model formulation the electroremediation system is divided into N+2 compartments corresponding to the soil and the two electrode chambers. The number of soil compartments (N) is selected high enough so to permit the study of electrical transport and diffusion effects in the soil with low numerical dispersion [1].

The model operates in two steps: first simulates species transport by integrating forward in time the one dimensional transport equation, then chemical equilibrium among the transported species is re-established. An iterative process between the two steps is carried out until a convergence criterion is achieved.

Four transport phenomena can be considered in the system: electromigration, electro-osmotic transport, diffusive transport and advection, and two kinds of reactions, electrochemical and chemical ones.

The electromigration includes the movement of ions from the soil and from the electrolyte towards the electrodes of opposite charge as well as of the protons and the hydroxyl generated ions.

Electroosmotic flow is calculated using the average drop potential through the soil compartment nad the electroosmotic permeability [2]. Direct and reverse electroosmotic flows can be switched depending on soil pH.

Diffusive transport of ionic species is negligible when compared to electromigration.

Advective transport is only specifically present in the electrode compartments where electrolyte is renovated but not within the soil because of no head difference between the two electrode compartments.

The electrochemical reactions considered are the reduction and oxidation of water on the electrodes that take place according to the expressions:

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2 H2O – 4 e- → O2 (gas) + 4 H+ Eo = - 1.229 (anode) (1)

2 H2O + 2 e- → H2 (gas) + 2 OH- Eo = - 0.828 (cathode) (2)

where Eo is the Standard electrochemical reduction potential.

No chemical reactions are considered for Cr (VI) but sorption which is taken as linear and pH dependent.

pH adjustments at the electrodes can be accounted for in the model by changing the concentration of H+ / OH- and increasing the concentration of nitrate or sodium ions accordingly.

As an internal consistency check, the program verifies that the electrical neutrality condition is met in every volume element at every time step [3].

RESULTS

The model has been calibrated using the results from several laboratory tests on a chromium (VI) contaminated soil [4].

The modelled system is a 20 cm length soil compartment. Base case conditions are: Chromium (VI) content in the soil: 4000 mg/kg, electrolyte composition 0.05M KNO3, constant voltage operation (15 - 30 V) and remediation time 7 days.

The effects of changing voltage, electrolyte ionic strength and pH have been explored and will be presented.

ACKNOWLEDGEMENTS

This work is part of an R+D project co-financed by Spain’s Ministry of Environment.

[1] Wilson, D.J., Rodríguez-Maroto, J.M., Gómez-Lahoz, C., (1995). Electrokinetic remediation. I. Modeling of simple systems. Sep. Sci. Technol. 30, 2937-2961. [2] Schultz, D.S., (1997). Electroosmosis technology for soil remediation: Laboratory results, field trial, and economic modelling. J. Haz. Mat. 55, 81-91. [3] Vereda-Alonso,C., Rodríguez-Maroto, J.M., García-Delgado, R.A., Gómez-Lahoz, C., Gracía-Herruzo, F., (2004). Two-dimensional model for soil electrokinetic remediation of heavy metals. Application to a copper spiked kaolin. Chemosphere 54, 895-903. [4] Nieto Castillo, A.M., Soriano, J. J., García-Delgado, R.A. (2006). Changes in chromium distribution during the electrodyalitic remediation of a chromium VI contaminated soil. In “Bioavailability of Pollutants and Soil Remediation”. Conference Proceedings pag 137.

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IMPLEMENTATION OF A IODIDE ENHANCED EKR TO A MERCURY CONTAMINATED SOIL

A. García-Rubio1, J. M. Rodríguez-Maroto1, F. García-Herruzo1, C. Vereda-Alonso1, C. Gómez-Lahoz1, J. M. Esbrí2 and P. Higueras2. 1Dpto. de Ingeniería Química, Universidad de Málaga. Málaga (Spain). [email protected] 2Departamento de Ingeniería Geológica y Minera, Escuela Universitaria Politécnica de Almadén, Universidad de Castilla-La Mancha, 13400 Almadén (Ciudad Real), Spain. The Almadén mining district constitutes one of the major concentrations of mercury on Earth. Located in south-central Spain is estimated to contain about a third of the known global mercury resources before mining (250000 t) (1). The mining activities began about 2000 years ago, and as expected the soils of the Almadén district are highly contaminated, with some zones displaying values well above 1000 ppm Hg. Higueras et al. (2) indicated that mercury has been introduced in the soils of the Almaden district via: a) geological dispersion, i.e., cinnabar particulate derived from the erosion of the mineral deposits and b) anthropogenic dispersion generated by the mining activity (transport and stockpiling, and metallurgical activities). High concentrations of Hg in aquatic organisms commonly used in biomonitoring programs of metal pollution have been detected and preliminary studies have revealed high levels of mercury absorption by plants (2). These facts put forward the need of soil decontamination. The remediation of mercury contaminated soil is difficult because of the low solubility of mercury and its compounds. Therefore, in order to enhance the electroremediation of this Hg contaminated soil, the use of a chelating agent is studied and iodide was chosen because it showed a 35 % extraction ratio in previous batch experiments. The electrokinetic experiments were performed in two different scales: large columns (50 cm2 cross section and 20 cm length) containing about 2 kg of water-saturated soil, and small columns (3.2 cm2 cross section and 2 cm length) with about 15.5 g of the same soil. The large scale experiments aim to provide results concerning to the Hg concentration profile along the column. Such results do not need to attain a complete remediation of the soil, which would require long-term experiments at this scale. Instead, the small scale experiments allow to achieve a complete remediation of the soil within a reasonable period of time. The later results can provide some theoretical bases for the optimal operation and design of the large-scale systems. All the experiments were performed at a constant current density of 1 mA·cm–2 and the pH of the electrolyte solutions were held to their respective constant values via a pH-control system of our own design and manufacture that allow on-line control of the pH values at the electrode compartments and monitoring of the rate of addition of reagent. The pH control was mainly used for two reasons: First, the supply of iodide ions to the soil can be easily regulated at the cathode by the addition of hydriodic acid (0.1 M); as a result the basic front is exchanged by an iodide front. Second, the addition of sodium hydroxide at the anode avoid the generation of the acid front, protons with a very high molar conductivity value are replaced by sodium ions that present a lower one, and therefore the fraction of electrical current carried out by iodide across the soil increases because its relatively contribution to the conductivity of the pore water increases too. The pH-control system in each electrode compartment consists of a graduated 100 ml burette that makes available the necessary volume of either hydriodic acid solution at the cathode or sodium hydroxide solution at the anode when the pH increases above or decreases below their respective target pH-values.

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At the end of the large scale experiments the soil columns were divided into 10 cross slices in which the total mercury content was measured. In addition, the BCR sequential extraction procedure (3) was performed for each of these slices in order to evaluate the mobility and availability of the mercury in the soil after the remediation. Likewise, the same procedure was performed at the end of the small scale experiment, but in this case the soil was not divided into slices. As an example, the figure shows the consumption of hydriodic acid (as mmol of iodide) at the cathode and sodium hydroxide (as mmol sodium) at the anode, for one of the small scale assays. The acid consumption rate (mol [HI] s–1) was equal within 2 % to the current intensity (mol [e–] s–1), whereas the NaOH consumption was slightly smaller, in agreement with the alkaline characteristics of the original soil. The figure also shows the Hg recovered at the anode (mercury was not significantly recovered at the cathode). The percentage of Hg recovered (below 37%) would suggest that the iodide enhanced electrokinetic treatment is not successful. Nevertheless, a comparison of the BCR results obtained before and after the treatments indicates that after the remediation, the mercury was effectively removed from the fraction of Hg associated to the reducible matter, whereas the one associated to the oxidizable matter was not. This oxidizable fraction together with the residual one are probably associated to cinnabar, which is naturally found at the Almadén district. In addition, the large scale experiments indicate that if the treatment is not completely accomplished, the mobility of mercury in the contaminated soil would increase, as can be concluded from the relative increase of Hg associated to the weak acid soluble fraction that we have obtained in the BCR speciation. Similar results have been found earlier (4).

0

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Acknowledgements: This research was funded by Grant PPQ2003-01902 (Spanish Ministry of Education and Science) and Project 148/2004/3 (Ministry for Environment). CGL and CVA acknowledge the economic support from the Junta de Andalucía through the program “Medidas de Impulso de la Sociedad del Conocimiento en Andalucia”. References: (1). A. Hernández, M. Jébrak; P. Higueras, R. Oyarzun, D. Morata and J. Munha. Mineralium Deposita 34, 539-548 (1999) (2). P. Higueras, R. Oyarzun, J. Lillo, J.C. Sánchez-Hernández, J.A. Molina, J.M. Esbrí and S. Lorenzo. Science of the Total Environment 356: 112– 124 (2006) (3) A.M. Ure, P. Quevauviller, H. Muntau and B. Griepink. Int. J. of Environ. and Anal. Chem. 51 (1-4) 135-51 (1993). (4) A.B. Ribeiro and J. M. Rodriguez-Maroto. “Electroremediation of heavy metal contaminated soils. Processes and application” Chap. 18 in Trace elements in the environment CRC Press (2006)

168


ELECTROKINETIC REMEDIATION OF A RADIONUCLID- CONTAMINATED SOILS

V. A. Korolev1, Y.E. Barkhatova1, E.V. Shevtsova2

Russia, Moscow, Geological Faculty of MSU named M.V. Lomonosov1 and NPO “Radon”2

E-mail: [email protected]

A lot of serious problems connected to pollution by radioactive substances of separate territories arise during the activity of the nuclear industry enterprises. The top layer of soils absorbs about 95 % of radioactive pollution. The results of the polluted territories researches and the experience of rehabilitation measures saved for 10 years after the failure on Chernobyl nuclear station, has shown, that soils are the basic collectors of radioactive substances. The majority of developed technologies soils decontamination is based on their washing by various reagents. They include the lixiviation processes and selective extraction of radioactive pollutants. The electrokinetic method is a new and perspective method of radioactive soil clearing. The opportunity of its application for soil clearing with the low ability filtration on a place of local pollution (in situ) there is it’s the main advantage.

In the given report the results of research of the factors influencing electrochemical clearing soils from Cs-137 and strontium are stated.

The experimental researches of the major electrochemical lixiviation factors as applied to a task of development of the industrial clearing soils technologies from pollutions are a basis of this work.

The following tasks were decided during our researches: 1. The development of an electrochemical lixiviation technique on a laboratory

and industrial installations. 2. The choice and substantiation of ecological-spare lixiviation on reagents for

the most effective translation of an element-pollutant in the mobile form. 3. The choice of perspective selective reagents for the translation Cs-137 in the

ionic form. 4. The development of ways intensification of electrochemical process at its

various stages. Samples of a soils whose selected in NPO "Radon", undergone by the man-

caused pollution Cs-137, as a result of a strait liquid radioactive waste were the object of research. The soil was submitted by the loam of glacial genesis, middle Quaternary of age (gIIms) with specific activity Cs-137 from 80 kBk/kgs up to 200 kBk/kgs. Also we studied the average loam and medium-grained sand fixed by the silica-alumina gel. It is used in places of storage of the radioactive waste as a shield. In these soils the known quantity of strontium or cesium in the form of ammonium salts simulating radionuclides, are contained. Their concentration in soils after the clearing was determined by the atomic absorptive analyzer.

The technique of experimental researches of electrochemical clearing of soils from the radionuclides consists of a several stages. At the first stage we studied properties of the polluted soils, prepared it for experiment, determined the Cs-137 activity in the polluted soils. At the second stage we selected the most suitable reagent for the lixiviation of Cs-137 from soils. At the third stage we spent electrochemical tests on laboratory installations with the use chosen reagents. At the following stage of researches we determined the quantities of macrocomponents and the residual quantity of cesium, taking place in a sample of soils, after the electrokinetic remediation.

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The experiments on clearing soils from salts of strontium and cesium were made in a single-chamber electrokinetic cell of an open type. The experiences have shown, that in a field of a constant electrical current the redistribution of these ions is carried out from the anode to the cathode both in a loam, and in the modified sand-gel soils. This result allows applying the given method to clearing from the radionuclide of protective sorption screens in the places of warehousing liquid radioactive wastes.

In experiments on clearing soils from Cs-137 we used of three-chamber electrokinetic installation. In them the anodic and cathodic chamber were separated from the central, filled by the polluted soils, neutral diaphragms and by the drainage from a polymeric material. The plates from the corrosion-proof steel (cathodes) and platinized titanium (anodes) were used as electrodes.

The prepared paste of soils was located in the central chamber of electrokinetic installation. During all experiment we entered into the anodi chamber desorbent reagents (NH4NO3 or KNO3) with the concentration 1 mole/l. For neutralization of alkali, which is formed in a catholite at the electrolyze of water, in the cathodic chambers we created pH< 1 at submission of the concentrated nitric acid. The extraction of Cs-137, acting in the cathodic chamber, we carried out by the replacement of catholite.

In the other series of experiments we wanted to increase the efficiency of electrochemical clearing from Cs-137 by the selection of the best reagent for the transforming radionuclide in the mobile form. Simultaneously we achieved reduction of the acidity soils, and revealed more sparing, and the ecologically safe conditions of decontamination. It will allow to lower the charges on the subsequent neutralization acidity, i.e. on more complete rehabilitation of the polluted territories from radioactive infection. On the basis of the data received at research of lixiviation Cs-137 from soils, we carried out experiments in comparison of efficiency of application nitric acid and phosphate electrolytes for the electrokinetic clearing of soils. As a result of preliminary researches we have decided to use as the electrolyte the mixed one-mole solutions of acids and them ammonium salts of the following structure: 1M H3PO4 + 1M NH4H2PO4 and 1M HNO3 + 1M NH4NO3.

The received results of a laboratory experiments have shown, that at clearing a radioactive soils as an ion-desorbent cation NH4

+ is more effective, than cation K+. The extraction Cs-137 with the use of solutions NH4NO3 almost twice is higher, than with use KNO3. The general degree of extraction Cs-137 in this case has made about 50 % and 30 % for the ammonium nitrate and potassium nitrate accordingly. These meanings almost in 5 and 3 times are higher, than without application of the specified salts.

As a result of the spent experiments we was established, that the highest parameters of clearing are formed at use complex reagents solution: 1-1,5 M H3PO4 + 1M NH4H2PO4. On the basis of these researches we propose the phosphate leaching solutions in quality of most perspective.

References [1] Shevtsova E.V. The research and development of physical-chemical bases of

electrokinetic clearing technology of soils from radionuclides. - Moscow, 2003, GUP MosNPO “Radon" (in Russian).

[2] Korolev V.A. 2001. The cleaning of soils from pollution. - 365 pp. MAIK/ Interperiodica Publ., Moscow (in Russian)

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ELECTROKINETIC REMEDIATION OF A SOIL CONTAMINATED

WITH HEAVY METALS IN A SCALE PILOT EXPERIMENT.

Lobo, M.Ca, Martinez-Iñigoa, M.J, Pérez-Sanza, A, Plaza, Aa, Alonso, Ja, Perucha, Cb. aInstituto Madrileño de Investigación y Desarrollo Rural Agrario y Alimentario. IMIDRA. Finca “El Encin” A-2. Km 38,2 Alcalá de Henares 28800 (Madrid). Spain. E-mail: [email protected] b AG Ambiental, S.L. C/ Isabel Colbrand, 10 - Local 57 28050 Madrid Spain.

Soil degradation due to contamination represents an increasing hazard that requires the

development of methods for soil remediation. The process of regeneration must

guarantee the permanence of the solution adopted, giving precedence whenever possible

to in situ treatments that would avoid the generation, transport and elimination of waste

products [1]. In the last decades, different authors have demonstrated the efficiency of

the application of a electric field to the soil in order to mobilize charged species that

migrates in the direction of the opposite charged electrodes [2,3,4,5,6] Electrokinetic

technology seems to be an adequate way to reduce heavy metals in the soil to safe

pollutant levels or enabling them to be removed by biological technologies [7].

In this work, it has been developed a pilot scale experiment with 1 tons of a clayed-

sandy soil treated with Pb, Cd, Zn and Cr.

The soils were artificially contaminated with heavy metal soluble salts in different

remediation assays: A: ZnCl2, B: Pb(NO3)2 + Cd (NO3)2 . 4H20 C: Pb(NO3)2 + Cd

(NO3)2 4H20 +K2 Cr2O7. . Heavy metal concentration was calculated as five times the

limit value according to European legislation in relation to sewage sludge agriculture

application [8].

Remediation experiments were carried out using graphite electrodes for both anode and

cathode and applying 100 volts direct current. Citric acid was used as purging solution.

Pumping was discontinuous to avoid that soil gets dried and a working pressure of 80

psi. was used.

A good mobility of the cationic contaminants was produced in the soil, however

the mobility of anion (chromium) was lower in the same conditions.

In soils with several pollutants (B and C), migration and removal of heavy

metals were depended on their initial concentration.

171

In general, short assays (less than 20 days) and low intensity of direct current

were enough to obtain good contaminants mobility in this type of soil. Nevertheless,

the total remove of soil pollutant were not achieved in this conditions. The residual

content was more difficult to remove being necessary to increase the current intensity

and the process time or the use of other complementary technologies.

Acknowledgments

This research was financed by Projects 094/2006/2-1.2 (Ministerio de Medio Ambiente)

and EIADES Program S-0505/AMB/0296 (Consejería de Educación. Comunidad de

Madrid).

References

[1]Comission of the European Comnuties 2006. Com (2006) 232. Proposal for a Directive for Soil Protection. http://ec.europa.eu/environment/soil/ [2] Acar, Y.B and Alshawabkeh, A.N., 1993. Principles of Electrokinetic Remediation. Enviornmental Science and Technology. Vol 27. Nº 13, 2638-2647. [3]Page, M.M., and Page, C.L, 2002. Electroremediation of contaminated soils. J, Environ. Eng. 128, 208-219 [4] Reddy, K.R. 1999 Journal of the Air & Waste Management Association 49 (823-830), [5] Reddy, K.R, Xu, Ch. Y and Chinthamreddy S. 2001. Assessment of electrokinetic removal of heavy metals form soils by sequential extraction analysis. Journal of hazardous materials. B84, 279-296. [6]Reddy, K.R, Saichek, R.E, Maturi, K and Ala, P, 2002. Effects of soil moisture and heavy metals concentrations on electrokinetic remediation. Indian Geotechnical Journal. 32 (2). [7] Lobo, M.C., Martínez- Iñigo, M.J , Alonso, J. Perucha, C., De Fresno, A , Laguna, J. 2003. Application of electrokinetic remediation to soil contaminated with heavy metals and organic compounds. Procc. 4th European Congress of Chemical Engineering. Granada (Spain) [8] Council of the European Communities.(1986): Directive concerning sludge amendments. Off. J. June, 12, L181/6

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ELECTROKINETIC REMEDIATION OF METAL-CONTAMINATED SOIL

Larisa L.Lysenko, Nataliya A.Mishchuk Institute of Colloid Chemistry and Water Chemistry of National Academy of Sciences of Ukraine, pr.Vernadskogo, 42, Kiev-142, Ukraine, 03680, [email protected]

Electroremediation of industrial contaminated soils from heavy metals is a very

important and complicated problem. One of the decontamination methods is based on a

mass transfer of polluting substances under action of an external electrical field with

their subsequent extraction from a cathode chamber. Transfer of components of soil

occurs by well-known phenomena, i.e. electrophoresis, electro-osmosis and diffusion

and depends on different accompanied factors. However, in spite of many years of

investigations the achievements in this area are not too promising, since the rate and

efficacy of remediation strongly depend on the chemical characteristics of soil and can

be very low.

Most important and effective process that causes the electrokinetic purification

of soil from charged pollutants is their electromigration (electrophoresis). To provide

the mobility of pollutants in an electric field, they should be not only desorbed from

complexes with soil components, but also during the whole process of soil remediation

should preserve their water-soluble form. However, due to a generation of hydroxyl

ions on a cathode and, correspondingly, by an alkalinity of water in the cathode

chamber and in the soil adjacent to it, the considerably part of metallic pollutants loses

their solubility and therefore decreases or loses their mobility in an electric field. The

value of pH also affects the process of pollutant adsorption and their mobility in soil,

i.e. the rate of soil decontamination Therefore the careful optimization of the known

methods of pH regulation or the development of new ways of pH regulation is one of

the most important problem of soil remediation that worthy of special attention.

The conducted theoretical analysis of all processes during soil remediation and

experimental investigations gave an opportunity to develop an original scheme of pH

regulation, which allowed us to accelerate and to enhance the soil decontamination. The

received experimental data concerning the purification of a sod-podzol soil, polluted

with nickel, cadmium and other compounds, have shown that the high degree of

remediation (more than 99%) during relatively short treatment is reached.

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ELECTROKINETIC REMEDIATION OF COPPER CONTAMINATED CLAY SOILS

Nataliya Mishchuk, Larysa Lysenko, Boris KornilovichA.V.Dumansky Institute of Colloid and Water Chemistry, Ukrainian Academy of Sciences, pr. Vernadskogo 42, 03680 Kyiv, Ukraine, [email protected]

To a large extent, effectiveness of electrokinetic techniques for decontamination

of metal polluted slurries and soils is determined by the chemical form of contaminants

in the environment. The easiest decontamination by electric field is can be reached for

the admixtures that exist in a free ionic state. At the same time, if there are rather strong

adsorption bonds between contaminating ions and active centres of the solid phase, their

removing will be extremely complicated.

Among the most important natural minerals are clays that are highly dispersed

and therefore, substantially determine colloid properties of soils. It is typical for clay

minerals to form strong surface complexes with heavy metals and other pollutants. In

contrast to the classic theory of specific adsorption in Stern’s electrical double layer

(EDL) according to a generalized model EDL that includes the idea of the features of

surface complex formation, metal ions that are part of these complexes complete the

crystal structure of solid phases, thus determining their potential Ψо. Rather mobile

outer-sphere complexes form Stern’s layer up to the outer Helmholz plane and the

diffusion part of an EDL.

The application of external electric field affects both the mobility of

charged admixtures and their complexation in a soil. Therefore, the findings of

traditional sorption experiments (in static and dynamic conditions) cannot be

completely ascribed to sorption processes that occur during electrokinetic soil

remediation.

The new way to look at the kinetics of metals removing in disperse systems is

developed in view of sorption-desorption processes in layers adjacent to the surface of

the mineral particles. The experimental results, which were received on model kaolinite

systems contaminated with copper, show good agreement with theoretically calculated

values, but in more complicated cases as real natural soils the agreement is not so good

and further development of proposed approach is needed.

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FUNDAMENTAL PROBLEMS OF SOIL AND SLUDGE DECONTAMINATION BY APPLICATION OF AN ELECTRIC FIELD

Nataliya A. Mishchuk Institute of Colloid Chemistry and Water Chemistry of National Academy of Sciences of Ukraine, pr.Vernadskogo, 42, Kiev-142, Ukraine, 03680, [email protected]

Remediation of industrial soils contaminated from radionuclides, heavy metals and other pollutants is a very important and complicated problem. Special attention deserves the process of soil recovering by application of an electric field. The method is based on the mass transfer of polluting substances under the action of the external electrical field, together with their subsequent extraction from the cathode chamber. Transfer of soil components can be achieved by electrophoresis, electro-osmosis and diffusion, osmotic and convective movement of liquid, and depends on many factors: soil chemistry and structure, desorption, ion exchange, polarization of soil particles and electrodes, electrokinetic mobility of pollutants etc., which affect the efficacy of the decontamination processes. Thus, a comprehensive approach to the detailed analysis of all proceeding processes and the development of new technological ideas is a matter of paramount importance.

Unfortunately, according to numerous investigations, the application of an

electric field in a wide range of voltage or current density shows rather low efficiency and/or rate of decontamination. It is astonishing that the strongest negative factor of soil remediation in an electric field is an electric field itself. An electrical current is always accompanied by the electrolysis of water on electrodes, which leads to the change of soil pH, creation of inhomogeneous local surface potential and conductivity of soil, inhomogeneous local solubility, as well as desoprtion and mobility of pollutants due to the field. The most negative role is played by alkalinity of soil near the cathode, where a considerable fraction of contaminating ions lose their solubility.

Prevention of the negative influence of soil alkalinity can be achieved in a few

ways: introduction of complexing agents, wetting of the soil by acid solutions, use of ion-exchange membranes, and conditioning of the catholyte pH. Each of these methods has some disadvantages. Introduction of complexing agents very often successfully averts the negative influence of an alkalinity, but the created complexes have lower mobility in the electric field in comparison with that of the contaminating ions. The wetting of soil by acids and the conditioning of catholyte pH, as well as the use of complexing agents need rather high amount of reagents and in fact bring about a secondary pollution of soil. Allocation of soil between cation- and anion-exchange membranes prevents the movement of hydroxyl ions into the soil. However, water splitting caused by polarization of membranes and/or creation of a bipolar contact between membranes and soil create ion fluxes similar to those produced on the electrodes. Therefore, the careful optimization of the known methods and the development of new ways of pH regulation is one of the most important problems of soil remediation worthy of special attention.

The conducted theoretical analysis of all processes during soil remediation under

theoretical investigations gave an opportunity to develop the scheme of pH, ion flux and electrokinetic potential regulation, leading to an acceleration and enhancement of soil

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decontamination from charged and non-charged pollutants. Theoretical results are compared with experimental data [1, 2, 3].

1. Коrnilovich B., Mishchuk N., Abbruzzese K., Pshinko G., Кlishchenko R., Colloids and Surfaces, A 265 (2005) 114–123

2. Mishchuk N., Коrnilovich B., Кlishchenko R., J. Colloid Interface Science. (in press)

3. Mishchuk N., Lysenko L. Chemistry and Technology of Water, Ukraine (in press)

176


REMEDIATION OF CADMIUM CONTAMINATED PADDY SOILS BY WASHING WITH CALCIUM CHLORIDE IN PINDI-BHATIAN

(PUNJAB) PAKISTAN Tahir Mehmooda, Syed Tasawar Abbasb, Kashif Shahbazb and Muhammad Bashirc

acDepartment of Soil Science, University College of Agriculture, Rawalakot, Azad Jammu & Kashmir University, AJK (Pakistan), Phone: 00923216220602; E-mail: [email protected] bROYAL CROP SCIENCE (Pvt.) Ltd. Multan, Pakistan. INTRODUCTION The soil in many Pakistani paddy fields (especially Faisalabad Division) has been affected by Cd derived from sludge of different chemical manufacturing industries. To ensure the safety of foods, the concentrations of Cd in staple crops should be below a standard value; this applies particularly to rice because 34–50% of the Cd intake by Pakistani people has derived from rice. Therefore, development of remediation methods for Cd-contaminated soil has become an urgent task to ensure food safety. OBJECTIVES 1. Identification of wash chemicals with minimal environmental impact on the paddy field and its surrounding environment, but with high Cd-removal efficiency. 2. Development of a cost-effective and environmentally sound soil-wash and on-site wastewater-treatment system that purifies the heavy metal-contaminated wastewater generated by the washing process. 3. Preservation of soil fertility and plant growth after the wash treatment. MATERIALS AND METHODS It includes the following; 1- Performance evaluation of chelating resin 2- On-site soil washing 3 Chemical washing 4. Water washing The CaCl2 (437 kg) (collected from Sitara Chemicals Industries LTD., Sheikhupura Road, Faisalabad, Pakistan was applied to the bounded experimental field, followed by 11.6 kL of canal water, creating a soil-solution ratio and a CaCl2 concentration of 1:1.5 and 0.1 mol L−1, respectively. Following the water addition, the initial water level of the experimental field was 32 cm above the subsurface impervious layer, providing total 29.74 kL of water in the filed. The soil solution was mixed by a 13-metric-hp cultivator for 1 h until it turned into slurry; the slurry was allowed to rest for 1 h and then mixed again for 1 h. After the second mixing, the slurry was allowed to rest again for 2 h, and then the supernatant of the slurry was drained off as wastewater. The experimental field was then filled with canal water until the water level reached the initial point following the reapplication of CaCl2 (147 kg) to the field. The resulting concentration of CaCl2 in the paddy field was 0.1 mol L−1. The slurry was then mixed, allowed to rest, and drained.

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RESULTS AND DISCUSSION Table 1. Effects of washing treatment on the concentrations of various chemical forms of Cd in soils

Sampling plot Soil Cd (mg kg−1 dry soil)

Exchangeable Weakly acid soluble Acid soluble Total

Before washing

Unwashed a 0.021 0.05 0.67 0.71

Washed b 0.020 0.27 0.68 0.71

After washing

Unwashed 0.022 0.26 0.67 0.71

Washed 0.010** 0.17** 0.57*** 0.59*** Significant at the **0.01 and ***0.001 probability levels. a Washed without CaCl2. b Washed with CaCl2.

Table 2. Effects of the washing treatment on yields and Cd concentration of two rice varieties

Rice variety Plot Yield (kg ha−1) Cd concentration (mg kg−1)

Shoot Paddy Shoot Paddy

Shaheen Basmati Unwashed 1025 385 1.118 0.250

Washed 999 394 0.235** 0.083*

Super Basmati Unwashed 622 NY a 1.281 0.438

Washed 641 NY 0.421* 0.126** Significant at the *0.05 and **0.01 probability levels. a No yield

CONCLUSION The soil-wash experiment revealed the effectiveness of in situ soil Cd removal, especially exchangeable fraction, with on-site wastewater treatment. However, the washing had no effect on rice yield, although it changed soil fertility properties, and the Cd concentrations in soil and paddy yield were lower in the washed plot than in the unwashed plot, confirming the wash effects.

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COMPARATIVE LEACHING REAGENT EFFECTS IN THE COURSE OF AN ELECTROREMEDIATION OF A SOIL

CONTAMINATED BY LEAD. S. Amrate1, B. Hamdi2, D. E. Akretche1,*, M. Pazos3, C. Cameselle3 and C. Innocent4

1 Laboratory of Hydrometallurgy and Molecular Inorganic Chemistry, Faculty of Chemistry, University of Science and Technology Houari Boumediene (USTHB), B.P. 32 El – Alia, 16111 Bab – Ezzouar, Algeria 2 Laboratory of Environmental Applied Materials, University of Science and Technology Houari Boumediene (USTHB), B.P. 32 El – Alia, 16111 Bab – Ezzouar, Algeria 3Laborator of Bioprocesses, Dept of Chemical Engineering, University of Vigo, Spain 4European Institute of Membranes (IEM), Place Eugène Bataillon, 34090 Montpellier, France * Nato Project n°98080 (2006)

ABSTRACT Soil contamination became a concerned problem giving rise to many laboratory studies in recent years. It is due to the fact that various phenomena and numerous factors can intervene as pollutants provoking serious dangers to the human health. Heavy metals are generated from the factors which are the most difficult to eliminate. Despite the fact that processes adapted to organic compounds are varied, those that treat heavy metals are underdeveloped.

Electrokinetic soil remediation is one of in situ process that has been recently developed. It is also called either electrodialytic or electroosmosis, and it combines the technique of electrodialysis with electromigration of ions in the contaminated soil. However, the physico-chemical soil–contaminant interactions that occur simultaneously during the process may limit the efficiency of contaminant transport. In effect, in many cases, the water dissociation near the electrodes produces both H+ and OH- ions. The increase of hydroxyl production can give rise to hydroxides precipitates in some cases. To prevent this phenomenon and enhance the decontamination acids can be added near the cathode to neutralize the OH- produced by water dissociation and complexing agent as EDTA can also be used to facilitate the metal desorption from the contaminated soil.

In this work, the electrokinetic remediation of an Algerian soil contaminated by lead is studied. The contaminant results from a battery manufactory located at 12 km in the east of Algiers near an agricultural area. Through collaboration between three laboratories, comparative studies have been performed. To enhance the electrokinetic process, the use of acetic acid, nitric acid, citric acid, oxalic acid and disodium salt of ethylendiaminetetraacetic acid has been examined. All results have shown that this soil presents a high buffering capacity, so it is necessary the addition of complexing agents to metal extraction. Either EDTA concentration tested obtained around 80% of metal extraction. Nevertheless, the extraction with citric acid only obtained 80% of extraction in one tested concentration (0.5M pH 1.5). Furthermore, this acid provokes white precipitate in some concentrations tested, especially at lower values. Oxalic acid or nitric acid were not able to extract significant metal quantities and acetic acid allows to extract until 37% of lead. It has been also noticed that the behaviour of the electric field gives rise to an explanation of the phenomena which take place inside the cell used.

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Thus, Both Voltage and electric current measurements are performed to show the electric field strength variation inside the soil for each case studied. Electrokinetic tests were carried out in a cylindrical cell (Teflon and Glass).

*Corresponding author. Tel.: (213) 21.24.72.98 , email : [email protected]

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FROM ELECTROREMEDIATION TO METAL VALORISATION

N. Sabba and D. E. Akretche Laboratory of hydrometallurgy and Inorganic molecular chemistry, Department of chemistry and physics of inorganic materials, Faculty of Chemistry, U.S.T.H.B BP32, El - Alia, 16111 Bab-Ezzouar, Algiers, Algeria Fax : 213-21247298, email : [email protected] ABSTRACT

Electrokinetic processes have been tested for soil remediation since 1990. Many experiments have been performed at a laboratory scale varying many parameters to improve the process and to treat each case according to the nature of soil. Recently, the new developments of the electromembrane processes in the solid matrix treatment, particularly in the soil remediation field allow expecting a new alternative in the metal extraction from ores. An in situ technique which combines the principle of electrodialysis with electromigration of ions in the solid can be envisaged. This fact has induced us to test it for the metal extraction from ores.

In this work, we discuss about electroleaching experiments with membranes similar to electrodialyses which have been carried out using typical samples of a Copper ore from Ougarta, a locality sited in the South West of Algeria. This ore contains copper (average percentage 6.5%) in various mineralogical forms where malachite (Cu2CO3(OH)2) is the predominant. The electromembrane process has been studied through the optimisation of some parameters such current density and liquid-solid ratio and the direct electrodeposition of copper has examined too.

All electrokinetic experiments have been performed using a five compartment Plexiglas cell with a working membrane area of 16 cm2. The two extreme compartments are composed of graphite electrodes immersed in a rinsing solution of molar H2SO4. The central compartment contains the ore immersed in an appropriate solution of a leaching reagent where the pH is fixed. On both sides of this compartment, two circuits are located and they contain 250 ml of sulphuric acid 0.1M. The membranes are disposed alternatively as in a classical electrodialysis, but the anion exchange membrane near the cathode is retired to allow the electrodeposition study.

Results have shown yields of 97% and the combination of electrolysis to the

process gives rise to a promising method where the number of units operation is reduced. It has been shown that a new development of electrokinetic technique can be envisaged.

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