| 013 | sari vilhunen | sari vilhunen uvc irradiation ...fi-50100 mikkeli, finland e-mail:...

Publications of the University of Eastern FinlandDissertations in Forestry and Natural Sciences

Publications of the University of Eastern Finland

Dissertations in Forestry and Natural Sciences

isbn 978-�952-�61-�0183�-�5

Sari Vilhunen

UVC Irradiation Based Water TreatmentA Study of UV Light Emitting Diodes, Atomic

Layer Deposited TiO2 and Novel Applications

UVC irradiation based water treat-

ment techniques presented in this

doctoral dissertation belong to a

wide group of Advanced Oxidation

Processes (AOPs). Even though AOPs

are extensively used and studied for

decades, novel approaches appear

constantly. The increasing need for

water treatment caused by e.g. the

rapidly broadening industrializa-

tion, population growth and the

awareness of the disadvantages of

many pollutants have urged for the

development of energy efficient and

environmentally sustainable water

treatment techniques. This doctoral

dissertation introduces the latest

material and methods in the field of

UV irradiation based AOPs.

dissertatio

ns | 013 | S

ar

i Vilh

un

en | U

VC

Irrad

iatio

n B

ased

Wa

ter Trea

tmen

t - A S

tud

y of UV

Ligh

t Em

itting D

iod

es...

Sari VilhunenUVC Irradiation Based

Water TreatmentA Study of UV Light Emitting Diodes, Atomic


SARI VILHUNEN

UVC irradiation based

water treatment

A study of UV light emitting diodes, atomic

layer deposited TiO2 and novel applications



13

Academic Dissertation

To be presented by permission of the Faculty of Sciences and Forestry for public

examination in the Auditorium in MUC, Mikkeli University Consortium, Mikkeli, on

October, 15, 2010, at 12 o’clock noon.

Department of Environmental Science

Kopijyvä

Kuopio, 2010

Editors: Prof. Pertti Pasanen,

Prof. Tarja Lehto, Prof. Kai Peiponen

Distribution:

Eastern Finland University Library / Sales of publications

P.O. Box 107, FI-80101 Joensuu, Finland

tel. +358-50-3058396

http://www.uef.fi/kirjasto

ISBN 978-952-61-0183-5 (Paperback); ISSNL 1798-5668; ISSN 1798-5668

ISBN 978-952-61-0184-2 (PDF); ISSNL 1798-5668; ISSN 1798-5676

Author’s address: University of Eastern Finland

Department of Environmental Science

Laboratory of Applied Environmental Chemistry

Patteristonkatu 1

FI-50100 Mikkeli, Finland

E-mail: [email protected]

Supervisors: Professor Mika Sillanpää, Dr. Tech.

University of Eastern Finland

Laboratory of Applied Environmental Chemistry

Mikkeli, Finland


Dr. Jurate Virkutyte, Ph.D.

U.S. Environmental Protection Agency

Cincinnati, Ohio, USA


Professor Juhani Ruuskanen, Ph.D.

University of Eastern Finland, Kuopio Campus

Kuopio, Finland


Reviewers: Associate Professor Marina Trapido, Ph.D.

Tallinn University of Technology

Tallinn, Estonia


Dr. Jukka Jokela, Ph.D

Technology Centre Ketek LTD

Kokkola, Finland


Opponent: Professor Riitta Keiski, Dr. Tech.

University of Oulu

Oulu, Finland


ABSTRACT

Advanced oxidation processes (AOPs) have widely been used in water and

wastewater treatment. The AOPs are constantly improved with the aim of

producing more energy efficient and environmentally friendly technology for

the growing need of the water treatment. In photochemical and photocatalytic

AOPs the sources of external radiation and novel photocatalytic materials are

constantly developed. In addition, new applications and combinations of

treatment processes emerge frequently.

Within this thesis, novel UV light emitting diodes (LEDs; 255, 269 and 276

nm) and atomic layer deposited (ALD) TiO2 was tested in aqueous phenol and

salicylic acid treatment. UV LEDs were also used in studying the inactivation

of Escherichia coli (E. coli). In addition, novel applications, i.e. water matrices,

for selected AOP was examined. Limited number of studies exist using AOPs

in treatment of the pre-coagulated surface waters, creosote contaminated

groundwater and 1,2-dichloroethane (1,2-DCE) containing water (washing

water from the plant manufacturing ion exchange resins). Therefore,

conventional UV/H2O2 system was employed in the treatment of the kind of

water matrices.

UV LEDs (with H2O2) were found to be feasible but need further

development due to the rather low radiation power. The applicability in E. coli

deactivation was, however, considered to be competitive in comparison to

other UV radiation sources. The TiO2 films prepared by ALD were discovered

to be useful in photocatalytic water treatment. Crystallinity affected to the

photocatalytic properties of the TiO2 films, i.e. the mixture of anatase and rutile

was the most efficient in salicylic acid destruction. The UV/H2O2 treatment of

different water matrices was successful in terms of TOC removal when pre-

coagulated waters and groundwater was used. TOC removal from washing

water was inefficient but the target pollutant 1,2-DCE was more readily

decomposed. Altogether, the novel materials and UV light sources tested were

considered to be feasible alternatives for the conventional ones and the

applications studied were mostly suitable for the selected AOP.

Universal Decimal Classification: 52-74, 546.215, 549.514.6, 621.384.4, 628.16.08,

628.16.094.3, 628.166

CAB Thesaurus: water treatment; polluted water; water pollution; pollutants;

oxidation; ultraviolet radiation; light emitting diodes; hydrogen peroxide;

radicals; titanium dioxide; catalytic activity; degradation; organic matter;

phenol; salicylic acid; Escherichia coli; inactivation; disinfection

Yleinen suomalainen asiasanasto: vedenkäsittely; jätevesi - - käsittely; saasteet

- - poisto; epäpuhtaudet - - poisto; hapetus; ultraviolettisäteily; ledit;

vetyperoksidi; titaanidioksidi; katalyysi; hajoaminen; orgaaninen aines; fenolit;

kolibakteerit; desinfiointi

Acknowledgements

The research work for this thesis was carried out at the

Laboratory of Applied Environmental Chemistry (University of

Kuopio, i.e. University of Eastern Finland since January 2010), in

Mikkeli during January 2007 – March 2010.

I am highly grateful for my supervisor Professor Mika

Sillanpää for giving me the chance to carry out all the studies

and for the guidance and encouragement during the entire era. I

am also grateful for my other supervisors Dr. Jurate Virkutyte,

for all the support she gave to me and for the excellent guidance

and criticism, and Professor Juhani Ruuskanen for the

advisements with the thesis. I gratefully acknowledge the

financial support from Environmental Science and Technology

Graduate School (EnSTe), city of Mikkeli, Mikkeli University

Consortium (MUC) and EU.

I express my gratitude to Associate Professor Marina Trapido

and Dr. Jukka Jokela, the reviewers of the thesis, for their

encouraging and constructive comments.

I am very thankful for my co-authors especially Ph.Lic. Miia

Vilve, M.Sc. Mikko Vepsäläinen and M.Sc. Heikki Särkkä for the

support and company. Also Professor David Cameron, M.Sc.

Marja-Leena Kääriäinen and M.Sc. Markus Bosund are thanked

for their contribution. I want to thank all the co-workers in the

LAEC of whom I have learned so many things. I especially

thank for Taija Holm for the assistant and excellent work done

in the lab, M.Sc. Eveliina Repo for the help with my work, M.Sc.

Heikki Isotalus for the comprehensive understanding and Dr.

Jaroslaw Puton for teaching me of the world of photochemistry.

I am also grateful to my friends along the years, especially

M.Sc. Salla Takala and our small group of chemists which I got

known to in the beginning of our studies eventually leading to

this point.

My sincere gratitude goes to my dear parents for always

supporting me and letting me do things in my way. Thank you

for everything you have done for me and for always being there

for me. I am also thankful for my dear sister Jossu for always

being my closest friend.

The most grateful I am for my beloved becoming husband

Sami for being extremely encouraging and persistent with me.

Thank you for supporting and loving me!

Lahti, Finland, September 2010

Sari Vilhunen

ABBREVIATIONS

ALD Atomic layer deposition

AOP Advanced oxidation process

CFU Colony forming unit

CN Cyanide

DBD Dielectric barrier discharge

DBP Disinfection by-product

DCE Dichloroethane

DOC Dissolved organic carbon

E. coli Escherichia coli

EDL Electrodeless discharge lamp

FID Flame ionization detector

GC Gas chromatography

LED Light emitting diode

LP Low pressure

MP Medium pressure

MS Mass spectrometry

MW Microwave

NOM Natural organic matter

PAH Polycyclic aromatic hydrocarbon

PUV Pulsed ultraviolet

RF Radio frequency

SD Surface discharge

TOC Total organic carbon

UV Ultraviolet

VOC Volatile organic carbon

XRD X-ray diffraction

XRR X-ray reflectivity

LIST OF ORIGINAL PUBLICATIONS

The thesis consists of a summary and the five original papers

which are referred to by Roman numbers (Papers I-V) in the

text.

I. Vilhunen S., Sillanpää M. (2009): Ultraviolet light emitting

diodes and hydrogen peroxide in the photodegradation of

aqueous phenol. J. Hazard. Mater., 161, 1530-1534.

II. Vilhunen S., Särkkä H., Sillanpää M. (2009): Ultraviolet light

emitting diodes in disinfection of water. Environ. Sci. Pollut.

Res., 16, 439-442.

III. Vilhunen S., Bosund M., Kääriäinen M.-L., Cameron D.,

Sillanpää M. (2009): Atomic layer deposited TiO2 films in

photodegradation of aqueous salicylic acid. Sep. Purif. Technol.,

66, 130-134.

IV. Vilhunen S., Sillanpää M. (2009): Atomic layer deposited

(ALD) TiO2 and TiO2-x-Nx thin film photocatalysts in salicylic

acid decomposition. Water Sci. Technol., 60, 2471-2475.

V. Vilhunen S, Vilve M, Vepsäläinen M, Sillanpää M (2010):

Removal of organic matter from a variety of water matrices by

UV photolysis and UV/H2O2 method. J. Hazard. Mater., In Press.

Author’s contribution:

Sari Vilhunen did all the experimental work and at least 90% of

the writing for the Papers I-V.

Contents

1 Introduction ................................................................................... 12

2 Aims of the study .......................................................................... 14

3 Background: Advanced oxidation processes ........................... 15

3.1 Chemical and photochemical oxidation .................................. 16

3.2 Photocatalytic oxidation ............................................................ 17

3.3 Non-UV based oxidation methods ........................................... 18

4 Recent developments in AOPs ................................................... 19

4.1 UV radiation sources .................................................................. 19

4.1.1 Pulsed UV lamps ........................................................................ 19

4.1.2 Excimer UV lamps ...................................................................... 20

4.1.3 Microwave electrodeless discharge lamps ................................... 21

4.1.4 Ultraviolet light emitting diodes ................................................ 22

4.2 Alternatives for UV radiation ................................................... 23

4.3 Photocatalysis .............................................................................. 24

4.3.1 Photocatalyst materials ............................................................... 24

4.3.2 Photocatalytic thin film preparation techniques ......................... 25

4.3.3 TiO2 modifications ...................................................................... 26

4.4 Enhancements for conventional AOPs .................................... 27

4.5 Novel applications and integrated treatment methods......... 29

5 Materials and methods ................................................................ 31

5.1 Characteristics of UV LEDs ....................................................... 31

5.2 Characteristics of atomic layer deposited photocatalytic thin

films .................................................................................................... 31

5.3 Treated water matrices ............................................................... 32

5.3.1 Synthetic model waters ............................................................... 32

5.3.2 Natural and wastewater samples ................................................ 33

5.4 Reactor designs and experimental procedures ....................... 33

6 Results and discussion ................................................................. 35

6.1 Experiments with UV LEDs ...................................................... 35

6.1.1 Phenol oxidation ......................................................................... 35

6.1.2 Disinfection study ...................................................................... 36

6.2 Atomic layer deposited TiO2 in salicylic acid degradation ... 37

6.3 Treatment of natural and wastewater samples with

conventional UV/H2O2 ..................................................................... 41

7 Conclusions and future perspectives ........................................ 44

8 References ...................................................................................... 46

12

1 Introduction

The extensive amount of pollutants in environmental waters,

ground and surface waters is caused by the rapidly broadening

industrialization and population growth. In certain areas the

load of contaminants exceeds the capacity of the receiving

aquatic environment causing not only severe environmental

problems but also serious impacts on human health. Fortunately

the awareness of the effects of many abundant harmful organic

substances and microorganisms has increased. Water

purification is the removal of contaminants, such as suspended

solids, bacteria, natural iron and chemical pollutants, from the

untreated water. Even though the follow-up of the environment

and especially drinking water has amended lately, the practices

in water treatment especially in many developing countries

need major improvements.

There are numbers of available techniques for the treatment

of contaminated soils and waters. However, the most important

step is to prevent the release of the contaminants into the nature

for example by wastewater treatment, especially, if the use of

environmentally persistent chemicals is extensive. For

minimizing the chemical load the unnecessary use of chemicals

should be avoided and when the chemicals are necessary they

should have desired function with a minimum toxicity (Anastas

and Warner 1998), thus the processes used need to be efficient

and optimized. In addition, the chemical products should be

designed so that at the end of their function they break down

into environmentally harmless products. Because of the

increasing industrial activities and the growth of population not

to mention of the limited water resources and the additional

challenge posed by climate change, the importance of the

wastewater treatment in coming decades is growing up.

Several photochemical, biological, physical and

electrochemical methods are used to treat different wastewaters

contaminated with organic compounds (Legrini et al. 1993;

13

Alnaizy and Akgerman 2000; Amor et al. 2005; Li et al. 2005).

Feasibility of the methods highly depends on the wastewater

content. Advanced oxidation processes (AOPs) consist of a wide

group of methods that have successfully been used in water and

wastewater treatment over the past decades (Legrini et al. 1993).

The advantages of the AOPs are rather fast reaction rate and the

non-selective nature allowing the treatment of multiple

contaminants at the same time. They also have the potential to

reduce the toxicity of the contaminants and even completely

mineralize the target compounds. In addition, the majority of

AOPs does not produce solid waste nor concentrate the waste

with the subsequent requirement for the further treatment.

Though AOPs have received extensive interest among scientific

community, their advantages are indisputable and it is still

worthwhile to further study and develop the methods and

explore new applications for these processes.

14

2 Aims of the study

Even though there are multiple AOPs already including various

combinations and modifications of the processes, the

development of these processes and urge for higher efficiencies

is still ongoing. The common intention is to develop a method

which is practical, suitable for different matrices, energy

efficient and enables significant cost savings. The aim of the

thesis was to assess novel materials and methods in AOPs and

evaluate the practical potential of some recent developments.

The specified aims were:

To evaluate the potential of ultraviolet (UV; 255, 265 and

276 nm) light emitting diodes (LEDs) as a radiation source in

aqueous phenol oxidation by UV/H2O2 method and in

disinfection of water i.e. for Escherichia coli (E. coli) destruction

(Papers I, II).

To assess the feasibility of atomic layer deposited (ALD)

photocatalytic thin TiO2 films with UV radiation in aqueous

salicylic acid decomposition (Papers III, IV). The model

substances phenol and salicylic acid were chosen since they are

aromatic compounds present in the natural waters and have

similar structure with many other pollutants.

To study natural and wastewater matrices as potential

applications for conventional UV/H2O2 method (Paper V). The

studied water matrices were pre-coagulated surface water,

groundwater contaminated with creosote wood preservatives

and industrial water containing 1,2-dichloroethane (1,2-DCE).

15

3 Background: Advanced

oxidation processes

AOPs have been used in various applications such as

decomposition of hazardous organic compounds and natural

organic matter (NOM) (Martínez et al. 2005; Goslan et al. 2006).

Some of the organic compounds present in the water may have

many undesired effects on the environment and human health

such as direct toxic effects (e.g. phenol) or they could disrupt the

physiological function of hormones (endocrine disrupting

chemicals, EDC) (Rosenfeldt and Linden 2004; Martínez et al.

2005). NOM is a mixture of organic compounds occurring in

surface water and groundwater. The removal of NOM from

drinking water by AOPs has recently been reviewed (Matilainen

and Sillanpää 2010). The presence of NOM in drinking water

has many undesired effects such as unpleasant odour, colour

and taste of water (Yildiz et al. 2007; Koparal et al. 2008). It also

reacts with chlorine, the most used oxidant in disinfection,

forming chlorinated disinfection by-products (DBP). In addition,

the NOM stimulate the growth of the micro-organisms in water

distribution pipelines. In order to avoid these adverse effects of

NOM present, it is necessary to apply different methods to

reduce the NOM content in the water.

It is well documented that during the AOP processes the

main reactive species, typically hydroxyl radical (HO•),

effectively degrades many refractory organic pollutants with

high reaction rates (Chang et al. 2007; Goldstein et al. 2007).

Common AOPs can be broadly classified into groups.

Photochemical and photocatalytic AOPs use UV radiation as an

external source of energy and among these groups there are UV

and hydrogen peroxide (UV/H2O2) (Poupopoulos et al. 2006),

photo-Fenton’s reaction (Kusic et al. 2006b), UV and ozone

(UV/O3) (Vilve et al. 2007) and UV and titanium dioxide

16

(UV/TiO2) (Chiou et al. 2008). As a combination to

aforementioned methods, a simultaneous application of

microwave (MW) power and UV radiation is found to enhance

the efficiency of photochemical processes (Ferrari et al. 2009). In

addition, there are chemical processes, e.g. Fenton (Kusic et al.

2006b) and O3/H2O2 method (Kusic et al. 2006a), mechanical, e.g.

ultrasonic (Mahamuni and Adewuyi 2009) and electrical

methods (Dhaouadi et al. 2009) available for oxidative water

treatment. In fact, electrochemical AOPs constitute their own

group of efficient water treatment methods.

3.1 CHEMICAL AND PHOTOCHEMICAL OXIDATION

In UV/H2O2 process, HO• is formed mainly when H2O2 is

photo-dissociated by UV radiation in the range on 280 – 200 nm

(Tchobanoglous et al. 2005). HO• can attack organic molecules

in a non-selective way by radical addition, hydrogen abstraction or

electron transfer. Attack by hydrogen abstraction causes removal

of hydrogen atom and results in a chain reaction where the

developed radical organic compound reacts with oxygen

producing a peroxyl radical (RO2•, R describes organic

compound). Two radicals can also combine to form a stable

product by radical combination which is a termination reaction.

The photo-Fenton type reaction employs ferrous (Fe2+) or

ferric (Fe3+) salts, H2O2 and UV light, and the role of the Fe2+ and

Fe3+ is to catalyse H2O2 in the radical production (Momani et al.

2004). The Fenton’s reaction occurs similarly but without UV

radiation producing HO• and HO2• radicals (Vilve et al. 2010).

In the photo-Fenton’s and Fenton’s oxidation the proposed

mechanism for the decomposition of hydrogen peroxide in

acidic solution mainly consists of the sequence of reactions

(Walling 1975). Acidic conditions are required for the reactions

to happen, which might limit the feasibility of the method in

many applications.

In O3/UV process the photolysis of ozone dissolved in water

leads to production of H2O2, which further decomposes to HO•

by direct photolysis or by dissolving in water to form highly

17

reactive hydroperoxide anion (HO2-) (Vilve et al. 2007). Then the

formed HO2- reacts with O3 producing HO•. During combined

O3/H2O2 process, H2O2 dissolves in water to form HO2- which

again reacts with O3.

UV treatment is also extensively used in water disinfection

since it is efficient and is not expected to cause any undesired

disinfection by-products in contrast to for example conventional

chlorination (Nurizzo et al. 2005). Efficiency of UV systems in

disinfection are based on the DNA molecule absorbing UV light

(maxima at 260 and 190 nm) which leads to the breakage of

DNA and further to fast destruction of bacteria (Soloshenko et al.

2006).

3.2 PHOTOCATALYTIC OXIDATION

The most researched semiconductor photocatalyst TiO2 is

utilized as a powder or as thin films (Epling and Lin 2002; Yu et

al. 2002; Karunakaran and Senthilvelan 2005). Also other

semiconductors have been used (e.g. ZnO and Al2O3) but to a

much lesser extent. TiO2 is n-type semiconductor which is

relatively inexpensive and chemically highly stable (Fujishima et

al. 2000). The photocatalysis with a semiconductor is initiated by

the absorption of a photon producing electron-hole pairs (e-/h+)

(Al-Rasheed 2005). The energy of the photon has to be equal or

greater than the band gap of the semiconductor. Generally

photogenerated electrons (conduction band) and holes (valence

band) on TiO2 surface produce various active oxygen species,

such as O2-•, HO•, HO2• and O• (Houas et al. 2001; Kemell et al.

2007). The radical species produced have the ability to

completely mineralize various organic compounds. In addition,

photocatalytic TiO2 has successfully been employed in water

splitting and in disinfection of water contaminated with several

pathogenic micro-organisms, although the efficiencies have

been rather low (McCullagh et al. 2007; Hernández-Alonzo et al.

2009). Especially interesting property of TiO2 is the

photoinduced superhydrophilicity i.e. the contact angle of water

is less than 10° under irradiation with UV, which promotes the

18

self cleaning function of the TiO2 surface (Langlet et al. 2006;

Pore et al. 2006).

3.3 NON-UV BASED OXIDATION METHODS

In aqueous solution ultrasound irradiation generates nucleation,

growth and implosion of the cavities leading to extremely high

local conditions of pressure and temperature allowing the

formation of reactive radicals, e.g. H•, HO• and O2-•, as well as

direct decomposition of organic material present (Segura et al.

2009). In electrochemical AOPs HO• is generated via direct

water oxidation on the anode or indirect electro-oxidation

involving in situ electrogeneration of Fe2+ and H2O2 through the

two-electron reduction of oxygen either separately or

simultaneously (Dhaouadi et al. 2009). The latter system is

usually employed in electro-Fenton system.

Even though the varieties of AOPs are wide, novel methods

and applications appear constantly. Some of the recent

developments are presented in this thesis.

19

4 Recent developments in

AOPs

4.1 UV RADIATION SOURCES

Within photochemical and photocatalytic AOP and UV water

disinfection, conventional technology is based on continuous

wave mercury vapor lamps. Both, monochromatic low pressure

(LP) lamps emitting radiation at 253.7 nm and/or polychromatic

medium pressure (MP) lamps (emitted light at the range of 700 –

200 nm) have been used commonly in water treatment.

However, the environmental concern of the mercury content

and the high energy demand of the mercury vapor lamps have

driven the search for other alternatives for UV radiation.

4.1.1 Pulsed UV lamps

Pulsed UV (PUV) lamp technology is a relatively new non-

mercury alternative. It is used especially in inactivation of

bacteria and viruses (Schaefer et al. 2007; Bohrerova et al. 2008;

Daryany et al. 2009). PUV produces polychromatic light

(intensity maxima at ~ 550 – 400 nm and 300 – 200 nm) at high

radiation levels by a high power electrical pulse discharged in

microsecond bursts creating an intense light pulse. The

discharge is in non-toxic rare gas, e.g. xenon or krypton. PUV

lamp can be either a flashlamp or a surface discharge (SD) lamp

type. A great benefit for PUV lamps is that they are instant-on

lamps, i.e. there is no need for warm-up time which is necessary

for mercury vapor lamps. In addition, the efficiency (energy

converted to light) is greater in comparison to MP and LP lamps.

However, the lifetime of flashlamp type PUV lamp has been less

than that of MP lamp, yet the SD type lamp is expected to have

longer lifetime (Schaefer et al. 2007).

20

For instance, PUV lamps showed much higher treatment

efficiency in E. coli deactivation than MP and LP lamps

(Bohrerova et al. 2008). LP and MP lamps were more or less

equal in E. coli deactivation but the efficiency of PUV was

approximately 2.4 times more than the efficiency of LP and MP

lamps at the same UV dose. Similar phenomenon, but with

smaller difference between the PUV and conventional lamps,

was observed with treatment of coliphages T4 and T7. Thus,

PUV lamps seem to be very promising alternative to

conventional continuous light sources, at least in disinfection.

4.1.2 Excimer UV lamps

Narrowband dielectric barrier discharge (DBD) excimer UV

lamps essentially produce monochromatic light from vacuum

UV (200 – 100 nm) to UVA (400 – 315 nm) depending on the gas

used (Asano et al. 2006; Li et al. 2006; Afzal et al. 2010). The

alternative gases used in excimer lamps are Xe, XeCl, Kr and

KrCl. The excimer lamps are robust and inexpensive system,

ecologically beneficial, free of mercury and the lamp lifetime is

long (Li et al. 2006; Zhang and Boyd 2000).

Excimer UV lamps have successfully been used in oxidation

of aqueous organic compounds (Baum and Oppenländer 1995;

Ikematsu et al. 2004; Oppenländer et al. 2005). Also the efficiency

of microbial inactivation has been studied (Naunovic et al. 2008).

Short emitted wavelength (172 nm) promotes the formation of

HO• directly from the water molecule and no additional

chemicals such as H2O2 are needed (Oppenländer et al. 2005).

However, as bubbling of the treated water with air or molecular

oxygen enhanced the treatment efficiency significantly, the

mineralization rate of model substances (1-heptanol, benzoic

acid and potassium hydrogen phthalate) was found to be

dependent of dissolved oxygen. The additional H2O2 (28.5 mM),

however, enhanced the treatment efficiency drastically when

nitrobenzene (4.1 mM) was used as a model substance (Li et al.

2006). In 20 min the nitrobenzene removal was over five times

higher than without H2O2 addition. Also TOC removal was

enhanced by 5-fold. The high efficiency of UV/H2O2 system

when short wavelength eximer lamps are used might be a

21

consequence of the high H2O2 absorption, which increases at

shorter wavelengths. However, it should be noted, that since the

absorption coefficient of water at 172 nm is high, the intensity of

the UV light will decrease almost 90% in 5 mm thickness of

water. Thus, the water path penetrated by the 172 nm UV light

is very short. Decomposition efficiency of anatoxin-a was

studied in different water matrices (Afzal et al. 2010). The initial

anatoxin-a concentration, pH or temperature did not have an

effect on treatment efficiency but the matrix decreased the

decomposition rate remarkably.

4.1.3 Microwave electrodeless discharge lamps

MW powered electrodeless discharge lamps (EDL) have widely

been used in recent years (Hong et al. 2007; Ferrari et al. 2009).

Electrodeless discharge lamps can generate light covering the

wide range of spectrum from infrared region to vacuum UV

when irradiated by electromagnetic field. Because the lamp does

not include electrode, longer lifetimes are expected (Asano et al.

2006). In MWEDL systems the lamps containing mercury have

been used. However, environmental risk-free gases (such as

xenon, nitrogen, helium, oxygen, hydrogen and argon, in

mixture or alone) are also feasible (Horikoshi et al. 2007).

The MWEDL systems have been studied thoroughly in

decomposition of dyes (Horikoshi et al. 2002a; Horikoshi et al.

2002b; Hong et al. 2007; Ferrari et al. 2009) and a herbicide 2,4-

dichlorophenoxyacetic acid (Horikoshi et al. 2003; Horikoshi et al.

2004; Horikoshi et al. 2007). The system has proven to have high

treatment efficiency even though the wide emitted wavelength

range may cause some of the radiation energy to get wasted.

The MWEDL has been used with TiO2 and H2O2 in laboratory

scale (Horikoshi et al. 2007; Ferrari et al. 2009). In addition the

system was found to be feasible in direct photolysis although

with a much lesser extend. 2,4-dichlorophenoxyacetic acid (0.1

mM) was treated in TiO2/H2O dispersion, with electrodeless

UV/MW system and with UV irradiation (with electrode Hg

lamp) alone (Horikoshi et al. 2003). The treatment efficiency of

UV/MW system was significantly higher. In the identical

conditions the decomposition rate of 50% was achieved with

22

UV/MW system and 33% with UV irradiation. The loss of initial

TOC (10 mg/l) was 33% and 20% for UV/MW and UV system in

30 min treatment time, respectively. Depending on a reactor

structure, MWEDL is expected to be feasible also in industrial

scale.

4.1.4 Ultraviolet light emitting diodes

Light emitting diode (LED) is a semiconductor p-n junction

device which emits light in a narrow spectrum, produced by a

form of electroluminescence (Crawford et al. 2005; Hu et al. 2006;

Khan 2006). LEDs are prepared by non-toxic materials and

consume less energy than traditional lamps, as they transform

greater amount of energy into light and waste little energy as

heat. Moreover, LEDs are mechanically durable and emit only

desirable wavelength. In addition, a compact size of a LED

might be a benefit in some applications.

Recently developed UV LEDs may provide a viable

alternative as a UV source in water treatment. The UV LEDs

utilized as a radiation sources in oxidation processes have

emitted the radiation at the longest UV wavelength range (UVA)

partly at visible light region 410 – 375 nm (Chen et al. 2005;

Wang and Ku 2006; Chen et al. 2007; Shie et al. 2008). TiO2 and

TiO2/Ag powder and TiO2 film have been used as photocatalysts

at the treatments. The studies showed the feasibility and

potential of UV LEDs in photocatalytic water treatment. Besides,

UV LEDs have been found to be suitable in disinfection even

though the long wavelength used (365 nm) (Hamamoto et al.

2007). The developed UV LEDs emitting short UV wavelengths

(even 210 nm) have appeared just recently (Taniyasu et al. 2006).

Since it is now possible to manufacture UV LEDs emitting UVC

radiation (280 – 100 nm), the chances in the field of AOPs and

water treatment are expected.

The special characteristics of the UV radiation sources

presented above are collected to the Table 1 for the comparison.

The UV sources have many advantages but also some

drawbacks. In polychromatic lamps (PUV and EDL) part of the

energy might get wasted, if the radiation is not completely in the

effective wavelength range. All the light sources presented can

23

be manufactured so that they contain no harmful materials and

are expected to have long lifetime when compared to

conventional LP and MP mercury vapor lamps. Also the energy

efficiency of the novel UV radiation sources is expected to be

mainly better than that of the conventional UV lamps.

Table 1. Comparison of different UV sources presented above PUV Excimer EDL LED

Radiation Polychrom. Monochrom., 354 - 126 nm

Polychromatic (infrared to vacuum)

Monochrom.

Energy Efficiency

Good Good n.a. Good

Lifetime Moderate to

long Long

Long (no electrode)

Long

Harmful Content

No No Hg,

alternatives exist

No

Draw-backs

Possible energy loss

in “inefficient” wavelengths

n.a.

Possible energy loss in “inefficient”

wavelengths, external

energy (MW) needed

Deep UV LEDs under

development (prices high

but efficiencies still low)

Special benefits

Instant on Robust Electric wires not needed ->

practicality

Robust, small size,

wavelength can be

selected

Used in Disinfection AOPs,

disinfection AOPs

AOPs, disinfection

n.a. - Information not available

4.2 ALTERNATIVES FOR UV RADIATION

MW irradiation has successfully been used with H2O2 to

produce HO• (Prasannakumar et al. 2009). The formation of

HO• in MW/H2O2 system occurs similarly to UV/H2O2, so that

the MW irradiation splits the H2O2 molecule into two radicals.

24

However, radicals can be generated by MW from alternative

sources. MW activated persulfate oxidation, with or without the

aid of activated carbon, has been found to be a feasible new

AOP. The efficiency is based on sulfate radical (SO4•-) formation.

The formation of SO4•- may initiate a series of radical

propagation and termination chain reactions similarly to HO•.

Radio frequency (RF) plasmas, also called microwave

plasmas, in water are interesting novel system for AOPs

(Maehara et al. 2008). When RF power is injected to water by the

electrode, the plasma is generated, surrounded by bubbles and

maintained locally on the electrode. Once again the main active

species is expected to be HO• formed in the plasma. In addition

for the radical generation, the formation of H2O2 through radical

recombination reactions has also been reported. The main

advantage of the process is that for the radical formation no

chemical addition is needed (Maehara et al. 2010).

4.3 PHOTOCATALYSIS

In photocatalysis, novel approaches appear frequently. The

development in photocatalytic materials, forms of catalysts (e.g.

particles and thin films) and preparation techniques of the

catalytic materials, for example thin films, is ongoing and fast.

However, the TiO2 is still the mostly used material in

photocatalytic systems.

4.3.1 Photocatalyst materials

The majority of the photocatalysts used are metal oxides

(Diebold 2003). The form of crystallinity of the photocatalyst is

significant in the photocatalytic applications. TiO2 has

amorphous and three crystalline phases: anatase, rutile and

brookite. Other metal oxides with the rutile structure are for

example SnO2, RuO2, CrO2, MnO2 and VO2. In case of TiO2,

anatase is mostly favored in AOPs but a minor proportion of

rutile has been observed to enhance the activity, such as in

commercial titanium photocatalyst Degussa P25 (anatase : rutile,

3 : 1) (Ohno et al. 2001; Hurum et al. 2003). Degussa P25 is a

25

standard material and consists of TiO2 nanoparticles. In addition

for the earlier mentioned photocatalyst materials, e.g. ZnO,

Al2O3, ZrO2, Fe2O3 and CdO have been used (Karunakaran and

Senthilvelan 2005; Kansal et al. 2007). Also the photocatalytic

efficiency of sulfides (ZnS and CdS) has been studied (Kansal et

al. 2007).

The photocatalytic nanoparticles have widely been used in

heterogeneous oxidation of aqueous organic compounds

because of their high photocatalytic activity and chemical

stability (Houas et al. 2001; Chiou et al. 2008). The exquisite

benefit explaining the high efficiency of nanoparticles is the

great surface area of the material per mass unit. However, the

difficulties in separation, recovery and reuse of the

nanoparticles due to their small particle size pose a challenge for

practical applications. Thus, the development of other catalyst

forms, i.e. thin photocatalyst films, nanowires and nanofibers

has increased (Pore et al. 2004; Giri et al. 2008; Zhang et al. 2009).

4.3.2 Photocatalytic thin film preparation techniques

Photocatalytic thin films, which are long-lasting and reusable,

have been prepared by many different physical and chemical

ways, e.g. sol-gel (Yu et al. 2002), spin-coating (Patil et al. 2003),

sputtering (Eufinger et al. 2007), pulsed laser deposition (Zhao et

al. 2008a) and chemical vapor deposition (CVD) method (Yu et al.

2002; Lim and Kim 2006). Atomic layer deposition (ALD)

technique (Aarik et al. 2001; Pore et al. 2004) is rather new film

preparation method. ALD is a modification of a CVD method

having a different way of introducing reactants into the

chemical reactor. It is a gas phase chemical process in which

usually two precursor chemicals react sequentially with a

surface depositing the film. For example in the deposition of

TiO2 film TiCl4 and H2O can be used as precursors (Aarik et al.

2001). Due to the self-limited growth of ALD method, it can be

used in coating three-dimensional objects with good uniformity

and variety of materials with nanometric level thicknesses and

excellent composition control (Kemell et al. 2007). Thus, the

substrate material plays a major role in photocatalytic activity of

the film. For example, the surface roughness affecting to surface

26

area of catalyst can be modified by using different substrate

materials.

4.3.3 TiO2 modifications

For a long time various combinations of TiO2 with other

metal oxides, such as TiO2/SiO2 and TiO2/Al2O3, have been

studied for photocatalytic purposes (Anderson and Bard 1997;

Adán et al. 2006). In addition to combining different oxide films,

the properties of TiO2 can be enhanced by modifications. The

applicability of TiO2 is limited by the high recombination rate of

electron/hole pair and wide energy band cap (about 3.2 eV for

anatase and 3.0 eV for rutile) (Mills and Le Hunte 1997). Thus,

pure TiO2 has very low photocatalytic efficiency in the visible-

light region (Wu et al. 2005; Li et al. 2007). The surface

modification is used to improve the photocatalytic efficiency

and to shift the band gap into the visible-light region enabling

the use of for example solar radiation in photocatalytic water

treatment. However, at the same time the UV activity should not

drop down substantially. A photocatalyst which operates under

visible light but has a weak activity under UV light could be less

efficient under solar irradiation compared to pure TiO2 with a

good UV activity.

The TiO2 surface has been modified by doping with various

metals e.g. Ag, Pt, Zn and Fe (Zhu et al. 2004; Li et al. 2007; Zhao

et al. 2008b) and with N, F, S and B nonmetals(Zhu et al. 2004;

Dong et al. 2009; Rehman et al. 2009). In doping the TiO2 particles

with metals, the optimum range of doping has been between

0.06 – 2.25% (Akpan and Hameed 2009). High amount of metal

cations might act as recombination centers and therefore the

improvements of efficiency are possible only at low dopant

concentrations (Hernández-Alonzo et al. 2009). Doping the TiO2

with various metals and nonmetals has increased the catalytic

activity in visible light according to a recent review (Rehman et

al. 2009). Besides TiO2, the surface of other oxides, such as ZnO,

can be modified similarly.

Especially N-doping of TiO2 has been studied widely in order

to enhance the photocatalytic activity of the TiO2 in the visible

light range (Chen et al. 2007; Prabakar et al. 2008; Songwang and

27

Gao 2008; Zhao et al. 2008a; Ananpattarachai et al. 2009).

Multiple methods have been used in doping of both particles

(anatase and rutile phases) and thin films. Among these

methods are sol-gel method (Ananpattarachai et al. 2009),

surface nitridation of rutile nanoparticles (Songwang and Gao

2008), atmospheric-pressure plasma-enhanced nanoparticles

synthesis (Chen et al. 2007), DC magnetron sputtering (Prabakar

et al. 2008) and pulsed laser deposition (Zhao et al. 2008a)

methods. The band gap for N-doped TiO2 has reported to vary

with different doping techniques. For example in the film

prepared by ion-beam-assisted deposition the band gap was

2.82 – 3.54 eV depending on the amount of nitrogen (TiO2-x-Nx, x

= 0.00 – 0.90) in the film (Wu et al. 2005). The photocatalytic

activity in the visible light range was enhanced by N-doping.

For instance, decomposition of volatile organic compounds

(VOCs) was examined by TiO2 and N-doped TiO2 and it was

found that the N-doped form possessed remarkably enhanced

treatment efficiency under visible light (Chen et al. 2007). In 60

min treatment time the model substance isopropanol (140 mg/l)

was completely decomposed with N-doped TiO2 whereas the

concentration in the sample treated by TiO2 was still about 70

mg/l. In addition, the decomposition rate of isopropanol was

faster with N-doped TiO2 when the UV radiation at the

wavelength of 364 nm was used.

4.4 ENHANCEMENTS FOR CONVENTIONAL AOPS

Sometimes process enhancements by e.g. catalysts and a

combination of AOPs are implemented for enhanced treatment

ability and better energy efficiency. Several enhanced and

hybrid methods are presented below. Although, the Fenton’s

reagent has been proven to be efficient in treating contaminated

wastewaters, the applicability of the method has been limited

since the low pH (typically <3) is needed for the efficient oxidant

production. The drawbacks of the process include the formation

of insoluble Fe(III) forms and the fact that HO• are not always

formed at neutral pH (Lee and Sedlak 2009). This has led to a

28

development of catalyst materials allowing the use of pH-

neutral conditions. The addition of phosphotungstate (PW12O403-)

into Fenton-like system provides a new homogenous alternative

for treating recalcitrant organic compounds efficiently at neutral

pH (Lee and Sedlak 2009). PW12O403- forms soluble complexes

with Fe(III) under neutral pH conditions. The substance is

reported to be relatively nontoxic and resistant to oxidation.

Another catalyst used is so called SBA-15. Iron containing SBA-

15 catalyst, prepared by co-condensation of iron and silica

sources under acidic conditions, is a mesostructured material

that has successfully been used in heterogeneous photo-Fenton

system at pH 5.5 (Martínez et al. 2005).

TiO2 films (anatase phase) prepared by ALD have recently

been tested in photoelectrocatalysis (Heikkilä et al. 2009). ALD

was considered to be suitable film preparation technique since it

provides excellent composition control and produces very dense

and uniform layers necessary in the photoelectrocatalysis. The

decomposition of model substance methylene blue was

noticeable enhanced by photoelectrocatalysis when compared to

photocatalysis. The decomposition rates after 240 min treatment

were 80% and 15% (UV: 340 – 410 nm). In both cases the

decomposition rate was observed to reach saturation at the

function of thickness, 150 nm in photocatalysis and 356 nm in

photoelectrocatalysis.

The efficiency of a novel system of two-stage oxidation

process UV-Na2S2O8/H2O2-Fe(II,III) at initial pH 7 has been

studied (Huang and Huang 2009). At first stage the model

compound bisphenol A was oxidized into less complex

compound with an advantage of the high oxidation potential of

sulfate radicals. In the second stage, traditional photo-Fenton

was employed to mineralize the formed compounds into CO2.

Sodium persulfate was found to be a potential alternative

oxidant even for extensive use.

29

4.5 NOVEL APPLICATIONS AND INTEGRATED TREATMENT

METHODS

Despite the extensive AOP literature the amount of applications

dealing with industrial wastewaters and other real water

samples is limited, since the studies are mainly performed using

model substances (Vogelpohl 2007). Especially phenol and

phenolic compounds are widely used as model substances

because of their toxic nature and abundance in natural waters.

However, there are several studies of treating dye wastewaters

by AOPs (Alaton et al. 2002; Schrank et al. 2007).

A groundwater pollutant 1,2-DCE has an environmental

lifetime over 50 years under reductive conditions and it is highly

toxic and carcinogenic (De Wildeman et al. 2004; Salovsky et al.

2002). In spite of that, there is a very limited amount of studies

focusing on treatment of 1,2-DCE containing wastewater by

AOPs. Recently conventional Fenton’s reagent has been studied

in treatment of 1,2-DCE containing washing water from a plant

manufacturing ion-exchange resins (Vilve et al. 2010). The

removal of 1,2-DCE was efficient with the treatment.

Not only organic compounds but also inorganic matter can

be oxidized into less harmful molecules. An example is highly

toxic cyanide (CN) which is abundant in a variety of

wastewaters as in automobile industry and can be destroyed by

oxidizing with conventional methods UV/H2O2, UV/O3 and

UV/H2O2/O3 (Mudliar et al. 2009). The combination of oxidants

was found to be the fastest in cyanide destruction and less

energy consuming compared to the other two methods.

Ultrasound has been employed to enhance the efficiency of

AOPs such as in conventional Fenton and Fenton-like process

containing zero valent metallic iron (Fe0) (Pradhan and Gogate

2010) and in a study where simulated solar radiation was used

in photo-Fenton and TiO2 photocatalysis instead of UV radiation

(Méndez-Arriaga et al. 2009). Also a combination of

TiO2/Fe2+/ultrasound was used and in all cases recalcitrant

model pharmaceutical substance ibuprofen was effectively

mineralized. A study of a novel Fenton-like system in where Fe0

was along with air bubbling showed that ultrasound as an

30

external energy improved the treatment efficiency significantly

when treating simulated textile wastewater (Zhou et al. 2009).

However, when UV radiation was used as an external energy,

the treatment efficiency was similar to the experiment with only

Fe0 and air bubbling. Also integrated heterogeneous ultrasound

photo-Fenton process with the earlier mentioned SBA-15 as a

catalyst has been applied (Segura et al. 2009).

AOPs can also be used in combination with a biological pre-

treatment, as has been done in coking wastewater treatment

using electrochemical oxidation (Zhu et al. 2009) and door-

manufacturing factories wastewaters where Fenton and

electrochemical oxidation were successfully tested (Beteta et al.

2009). Also ozonation and O3/H2O2 treatment have been

employed as a tertiary treatment of pulp and paper mill

wastewaters (Salokannel et al. 2007). However, using AOPs

prior to biological treatment biodegradability can be improved

and toxicity reduced leading to the enhanced total

mineralization (Mantzavinos and Psillakis 2004; Comninellis et

al. 2008). This method has been used in treatment of several

wastewaters such as olive mill, paper mill and antibiotics

formulation effluent as reviewed recently (Mantzavinos and

Psillakis 2004).

In summary, there are multiple possibilities to integrate

water treatment methods, AOPs with each others or AOPs with

e.g. biological processes. Without a doubt the method

combinations are not always more efficient than the individual

methods but sometimes different treatments might work

synergistically together leading to a major energy, chemical and

time savings.

31

5 Materials and methods

5.1 CHARACTERISTICS OF UV LEDS

The UV LEDs were manufactured by Seoul Optodevice CO.,

LTD, Korea. Four distinct types of UV LEDs were utilized: three

of those emitted radiation at viewing angle 120° with different

wavelengths, i.e. 255, 269 and 276 nm. The fourth UV LED type

emitted radiation at ~265 nm with the viewing angle 15°. Ten

pieces of each UV LEDs was encapsulated when constructing

four batch reactor type systems for water treatment (Paper I).

Two of the systems (269 and 276 nm) were used also in

disinfection study (Paper II).

The efficiency of UV LEDs was determined by measuring

radiant flux using an integrating sphere (Gigaherz optik/Mitaten

Oy). The obtained values were 3.1, 5.8, 11.6 and 4.3 mW for UV

LED reactors emitting radiation at 255, 269, 276 (120°) and ~265

(15°) nm. The measurement of radiant flux was needed for

calculating the amount of photons absorbed in the sample

which was determined from radiation power flux at wavelength

λ and absorbance of the sample at λ. The comparison of

treatment efficiencies between the different LED types was done

by the quantum yield values (Ф) calculated from the amount of

destroyed model substance and the amount of photons

absorbed (Paper I).

5.2 CHARACTERISTICS OF ATOMIC LAYER DEPOSITED

PHOTOCATALYTIC THIN FILMS

Atomic layer deposited TiO2 films were prepared on glass

(circular plate, 20.4 cm2) and silica (square plate, 16.0 cm2)

substrates using titanium tetrachloride (TiCl4) and water as

precursors (Aarik et al. 2001). Varying the deposition

temperatures (150 – 450°C) affected to the crystallinity of the

32

material which is an essential factor in photocatalyst efficiency.

The crystallinity of TiO2 films was characterized by Phillips

X’pert X-ray diffractometer (XRD) using CuKα radiation (λ=1.54

Å). Film deposited at 150 °C did not show any crystalline

structure implying that the film was amorphous. At films

deposited at temperatures of 250 °C and 300 °C, only anatase

phase was found to exist while at temperatures 350 °C to 450 °C

the rutile phase was also found. In fact, in the film deposited at

the highest temperature, the rutile phase dominated.

Commercially available Pilkington ActiveTM was studied as a

reference sample (Pilkington, UK) (Mills et al. 2003). The

properties of TiO2 films (thickness, mass density and surface

roughness) were studied by using X-ray reflectivity (XRR)

measurements (Philips X’pert Pro) (Bosund et al. 2008). In

addition to pure TiO2 film, the efficiency of 15 nm thick N-

doped TiO2 film (on top of 50 nm of TiO2) was also tested. The

TiO2-x-Nx and one TiO2 film (deposited at 350 °C) was prepared

and characterized by Advanced Surface Technology Research

Laboratory (ASTRaL, Lappeenranta University of Technology,

Mikkeli, Finland). Since the TiO2-x-Nx film was under

development, detailed characteristics are not presented.

5.3 TREATED WATER MATRICES

5.3.1 Synthetic model waters

In all AOP experiments, except with the flow-through

photoreactor, model substances were used to evaluate the

efficiency of the treatment (Papers I, III, IV). The model

substances, phenol in UV LED experiments and salicylic acid in

TiO2 studies, are aromatic compounds present in environmental

waters and have similar structure to the many other potential

environmental pollutants. The initial phenol concentration used

was 25 – 200 mg/l and salicylic acid 10 and 75 mg/l.

In disinfection study different test mediums were tested in E.

coli (K 12) destruction (Paper II). The microbial number in

treated waters was approximately 107 colony forming units

(CFU) per cm3. The effect of test medium was examined with

33

ultrapure water, nutrient water (2 g of LAB 103 to 500 ml of

ultrapure water) and nutrient water with humic acids. The

amount of model humic acid was 4.4 g/l.

5.3.2 Natural and wastewater samples

The experiments with flow-through photoreactor were

performed with different waters that required treatment (Paper

V). Finnish surface water (1) including NOM was pretreated by

chemical- or electrocoagulation. The other two water matrices

containing harmful organics were groundwater contaminated

with creosote wood preservatives (2) and 1,2-DCE containing

(28 ± 4 mg/l) washing water (3) from the plant manufacturing

ion exchange resins. The organic portion of creosote consists

mainly of the polycyclic aromatic hydrocarbons (PAHs), many

of which are considered to be toxic, carcinogenic and

bioaccumulating (Shemer and Linden 2007). The total PAH-16

concentration of groundwater was 711 μg/l, of which 96%

consisted of naphthalene, acenaphthene, fluorene and

phenanthrene. In 1,2-DCE containing water the total organic

carbon (TOC) content was rather high, 42.0 mg/l when

compared to the rest of the treated waters in which the initial

TOC was 3 – 6 mg/l.

5.4 REACTOR DESIGNS AND EXPERIMENTAL PROCEDURES

In oxidation and disinfection studies with UV LEDs a simple

batch reactor was used. The radiation source was above the

water sample in a dish and magnetic stirrer was used for

agitation (Papers I, II). H2O2 was used as a HO• source with

H2O2:phenol molar ratio ranging from 5 to 150. The initial pH

was always between 6 and 7. A long treatment time (0 – 360 min)

was needed because of the low UV light intensity of the UV

LEDs.

The system for TiO2 experiments was similar. Coated plate

was placed at the bottom of a Petri dish and the sample solution

was poured on the top of the film (Papers III, IV). A UV light

source (low-pressure mercury arc lamp) was located above the

34

sample. The intensity of UV light on the sample surface was 0.2

mW/cm2 emitting 85% of the radiation in the range of 260 – 250

nm. The experiments were conducted at pH values 3 – 10 (pH of

the solution without adjustment was 4.2 – 4.3). No other

additional chemicals were used in the experiments. The

treatment time varied from 0 to 180 min.

The third reactor type was re-circulated flow-through

photoreactor with a sample bottle, magnetic stirrer, pump and

UV light (Paper V). The intensity of the UV light (254 nm)

reactor was 24.4 mW/cm2. H2O2 addition (25 – 200 mg/l) was

done to as-received waters. The sample volume used was 1.1 l

and the treatment time was 0 – 90 min. The water flow rate 1500

ml/min was selected to ensure proper mixing and steady flow of

the water.

All the experiments were conducted at room temperature (~

23 °C). In every case, also dark experiments without UV

radiation were performed. All the samples were analyzed

immediately after the experiments with suitable analytical

instruments. The decomposition of model substances was

verified by gas chromatography with flame ionization detector

(GC-FID) or gas chromatography with mass spectrometry (GC-

MS). In some experiments also TOC and UV absorbance

measurements were performed. The detailed analysis methods

are described in Papers I – V.

35

6 Results and discussion

6.1 EXPERIMENTS WITH UV LEDS

In experiments with UV LEDs the main focus was on finding

differences in the treatment efficiency when using reactors

emitting distinct wavelengths. Explicit differences were found,

indeed, in both oxidation (Paper I) and disinfection (Paper II)

study. However, other factors studied remarkably affected to

the efficiency of water treatment as well.

6.1.1 Phenol oxidation

In the experiments applying UV LEDs and H2O2 the degradation

rate of a model substance phenol (100 mg/l) was found to be

dependent of the wavelength used. Since the radiant fluxes were

not equal between the different LED types the straightforward

comparison of the treatment efficiencies using percentual

phenol decomposition rates is not advisable. Quantum yields,

taking into account the radiant fluxes, of phenol degradation

revealed the most efficient wavelength to be 255 nm. The

quantum yields of phenol degradation at different wavelengths

were 0.33, 0.24, 0.23 and 0.22 for UV LED reactors emitting

radiation at 255, 269, 276 (120°) and ~265 (15°) nm. Thus the

viewing angle of the LEDs did not have significant effect on

phenol decomposition. The efficiency of the short wavelength

was concluded to be a consequence of the greater absorbance of

H2O2 leading to higher production of HO•. In addition, weaker

absorbance of phenol at the shortest wavelength used was

expected to enhance the reaction rate since the higher amount of

UV radiation reached the main target, H2O2. The direct

photolysis of phenol was found to be insignificant.

The effect of initial H2O2 concentration to phenol

decomposition rate was found to be mostly irrelevant at the

studied range. At H2O2:phenol molar ratio of 25 – 150, no

significant differences were observed. However, at molar ratio 5

36

the treatment efficiency was reduced into half of the higher

molar ratios. The results are in accordance with the previous

studies utilizing the conventional UV lamps (Kusic et al. 2006a).

It has also been noted that at higher H2O2:phenol molar ratios

the oxidant starts to inhibit the reaction by well known HO•

scavenging effect thus deteriorating the reaction rate (Alnaizy

and Akgerman 2000).

The initial phenol concentration affected to phenol

decomposition rate when the H2O2:phenol molar ratio was kept

constant. With the highest concentration the amount of

degraded phenol was the highest even though the reaction rate

seemed to be the lowest when considering the percentual

degradation rate. An explanation might be that with higher

amount of phenol present the more available the compound is

for HO• attack.

The UV LEDs used in this study were rather weak in energy

input/output efficiency. However, since the fast development,

recently manufactured LEDs are much more powerful, than the

ones in question which were manufactured at early 2007. So,

even though the LEDs used in the current study were not

applicable in larger scale the newly developed ones might be

more competitive. Also the prices have decreased and the types

of LEDs increased enabling the use of LEDs in various

applications.

6.1.2 Disinfection study

The study with the UV LEDs emitting wavelengths 269 and 276

nm showed that also the efficiency of disinfection is dependent

on the wavelength used. The bacteria reduction rate during the

first 5 min was 3 – 4 log CFU/cm3 in both cases but it should be

noted that the radiant flux for a set of ten 276 nm LED was

doubled to the 269 nm LEDs. No bacteria could be detected after

25 min treatment time in either of experiments thus the

treatment efficiencies were concluded to be more or less the

same. The greater absorption and breakage of DNA at the

wavelength 269 nm presumable increases the efficiency of the

shorter wavelength compared to 276 nm (Soloshenko et al. 2006).

37

The impact of the test medium was also studied. The

deteriorating effect of the test mediums, nutrient water and

nutrient water with humic acids, was partially explained by the

greater UV absorbance, thus, it is possible that some of the

radiation was spent on reactions of humic acids and nutrients.

Humic acids have also reported to have a tendency of coating

the bacteria reducing the sensitivity of the cells to UV radiation

(Canwell et al. 2008).

Thus, the selection of the best wavelength is not easy, if the

water to be treated contains many UV absorbing species. For

example in disinfection studies the absorbance maximum of the

test medium should be noted. For example in our study the

absorbance of the test mediums at 269 nm were higher than at

276 nm (Paper II).

6.2 ATOMIC LAYER DEPOSITED TIO2 IN SALICYLIC ACID

DEGRADATION

Atomic layer deposited thin films were found to be

photocatalytically active and efficient in degradation of a model

contaminant – salicylic acid in aqueous solution (Paper III). The

films deposited at the highest temperatures (400 – 450 °C)

containing both anatase and rutile crystalline forms showed the

greatest photocatalytic efficiency (Fig. 1). The anatase containing

films (250 – 300 °C) were less efficient and the one deposited at

higher temperature was the better one.

Pore et al. found that when the TiO2 film was prepared using

TiCl4 and H2O as precursors in ALD process and the process

was modified by H2S the formation of rutile was more extensive

than in the process without modification (Pore et al. 2007). Also

the band gap energy (eV) was lowered by 0.1 – 0.2 eV. Even

though the amount of sulfur on the film was not substantial, the

effect on photocatalytic activity of modified film was

remarkably enhanced in both UV and visible light region with

the certain deposition parameters. Also the unmodified TiO2

contained rutile, thus the only reason could not be the existence

of rutile phase. However, the result was reverse in a study

38

where methylene blue was used as a model compound and TiO2

film was prepared by ALD using tetrakis(dimethylamido)-

titanium and H2O as a precursors (Lim and Kim 2006). The films

were amorphous at first and needed to be post annealed. The

films containing only anatase phase were photocatalytically the

most efficient and the increasing amount of rutile decreased the

efficiency. This implies that the preparation method and

precursors have an impact on the photocatalytic properties of

the thin films. Besides, the photocatalytic activity of the rutile

and anatase phases is expected to be dependent of a compound

to be oxidized (Hoffmann et al. 1995).

With ALD, it is possible to achieve positive synergistic effect

of the anatase and rutile in thin film form. Even though the

rutile has often been stated to be photocatalytically much less

active than anatase (Fox and Dulay 1993; Hoffmann et al. 1995),

the recent studies show, that rutile can be more active even in

the films were the amount of rutile is higher than anatase (Pore

et al. 2007 and Paper III).

20

30

40

50

60

70

80

90

100

0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 2,2

UV dose (J/cm2)

C/C

0 (

%)

Anatase (250°C) Anatase (300°C)

Anatase* + Rutile (400°C) Rutile* + Anatase (450°C)

Reference - Pilkington

Figure 1. Decomposition of salicylic acid with TiO2 films deposited at 250 – 450 °C

and Pilkington ActiveTM (c = 10 mg/l, pH 4.2). *Dominating form of crystallinity.

39

The initial pH values 6 and 8 were found to be the best ones

for efficient salicylic acid degradation when the film deposited

at 350 °C was used (Paper IV). Altogether, pH from 4.3 to 8 was

found to be feasible (Table 2). At pH 10 the efficiency was

remarkably lower and at pH 3 the worst. With the film

deposited at 300 °C pH 8 was recommended and only at pH 3

the treatment efficiency was clearly decreased (Paper III).

Therefore, the pH to be used for the maximum efficiency is

expected to be slightly different according to the crystallinity of

the film in question.

Table 2. Effect of initial pH on salicylic acid (10 mg/l) degradation (%) in 1 h

experiment (DT=deposition temperature). Salicylic acid degraded (%)

pH DT 300 °C DT 350 °C

3.0 16.9 20.9 4.3 (no adjustment) 34.0 42.6

6.0 32.6 58.0 8.0 49.8 49.6 10.0 35.6 23.7

In the previous studies the photocatalytic degradation was

found to be the fastest in alkaline solutions whereas the

adsorption of salicylic acid on TiO2 surface has been the weakest

(Hidaka et al. 2006; Li et al. 2007). Thus, the overall degradation

was influenced by other factors than adsorption such as greater

quantity of OH- and/or H2O molecules remaining on the surface

after chemisorption favouring larger rate of radical production

in alkaline media. Moreover, compared to molecular salicylic

acid more reactive ionic form is present in alkaline solution.

Also the reverse results can be found where both adsorption

and photodegradation were promoted at the same acidic pH

when suspended TiO2 ceramic membranes were used (Tunesi

and Anderson 1991) indicating a different degradation

pathways. However, the effect of pH is more complex. The

surface charge of TiO2 (isoelectric point ~6.5) is different in

strong acidic and basic conditions TiO2 existing in the forms of

TiOH2+ and TiO-, respectively (Lee et al. 2003). Salicylic acid is a

weak acid and acts in a same manner existing as a positive or

negative ion in strongly acidic or basic conditions. In

40

consequence, the same kind of charge might result an

electrostatic repulsion between catalytic surface and salicylic

acid which possibly reduces the contacts of active radicals and

model substance lowering the degradation rate.

When comparing the use of thin films to TiO2 particles, the

pH value for the maximum treatment efficiency has been

considerably different. With TiO2 particles the acidic pH has

usually been the optimum also when treating salicylic acid

(Akpan and Hameed 2009). However, with particles the

decomposition reaction would occur mainly via adsorption of a

model substance onto TiO2 particle surface and thus different

reaction pathways are expected. Control experiments without

UV radiation did not show any significant decrease in salicylic

acid concentration, thus the adsorption of salicylic acid onto

TiO2 surface was negligible. Therefore, the degradation was

attributed to the formed HO•.

In addition to the experiments utilizing TiO2, also N-doped

TiO2 film was tested with the UV (254 nm) radiation source

(Paper IV). The film, however, showed reduced activity in

salicylic acid degradation compared to pure TiO2 film. The

deposited film might have had similar demerits as in previous

study (Pore et al. 2006) where the estimated band gap energies

were not remarkably reduced with N-doped films prepared by

TiCl4 + H2O and TiCl4 + H2O + NH3 with nitrogen atomic

concentrations 0.8 – 3.8% (3.1 – 3.4 eV) when compared to bulk

TiO2 (3.2 eV). Even though band gap was slightly reduced with

nitrogen atomic concentration 8.1% (2.9 eV) the film in both UV

and visible light was photocatalytically less active than the non-

doped TiO2. The explanations were that the N-doped films had

weakened photoinduced superhydrophilicity and they suffered

from the high recombination lowering the photocatalytic

activity. However, in the same study TiN film annealed in air at

500°C producing N-doped rutile was able to destroy stearic acid

in the visible light range but the activity in UV light was rather

insignificant when compared to TiO2 film (Pore et al. 2006). The

adequacy of visible light irradiation for the induced

photocatalytic activity of as-prepared TiO2 films should have

been tested.

41

The energy efficiency as well as other environmental aspects

should be taken account in UV/TiO2 treatment. Thus the use of

solar radiation should be expanded also into industrial water

treatment. Novel doped and combined TiO2 materials emerge

constantly with the aim of usage of visible/sun light with the

photocatalyst (Prabakar et al. 2008; Zhao et al. 2008a). Materials

which are photocatalytically active in visible light region

already exist, thus, the usability of solar radiation even in large

scale and/or in industrial water treatment systems might be

conceivable in near future.

6.3 TREATMENT OF NATURAL AND WASTEWATER SAMPLES

WITH CONVENTIONAL UV/H2O2

The conventional UV/H2O2 method was mostly efficient in

purification of natural and wastewater samples (Paper V). The

removal of organic matter using UV/H2O2 method was efficient

when the initial TOC concentration was low (Table 3). Even

though the UV photolysis and UV/H2O2 treatment have

successfully been used in removal of NOM from the natural

water (Wang et al. 2000; Goslan et al. 2006) the efficient treatment

might require considerably great UV doses and/or H2O2

concentrations, if the UV absorbance of the water is high. In

such cases, removing the majority of the organic material by

other method, such as electrocoagulation, prior to the oxidation

treatment, might result in elevated overall NOM mineralization

and reduced operating cost (Yildiz et al. 2007; Koparal et al. 2008;

Vepsäläinen et al. 2009).

42

Table 3. Removed TOC (mg/l) during 60 min treatments with UV and UV/H2O2

(removal% in parenthesis).

Water matrice Initial TOC

(mg/l)

TOC removed (mg/l)

UV UV + 1.5 mM

H2O2 UV + 3 mM

H2O2

Chemically coagulated water

3.8 0.5 (12%) 3.2 (86%) 2.7 (73%)

Electrocoagulated water

5.6 0.5 (9%) 3.7 (66%) 3.9 (70%)

Groundwater (PAH contamination)

4.4 0.9 (22%) 2.4 (54%) 3.3 (76%)

Washing water (with 1,2-DCE)

42.0 2.8 (7%) 5.4 (13%) 6.9 (16%)

The TOC removal in % from washing water in the presence

of UV and 1.5 – 3 mM H2O2 was not considered to be efficient

(Table 3). The better efficiency (31%) was achieved with UV + 6

mM H2O2, however, leading to a high H2O2 residual

concentration. Thus, longer treatment time would have been

needed to reduce the TOC concentration efficiently. In the

treatment of similar water with higher contamination rate with

Fenton’s oxidation, better treatment efficiencies were achieved

but with the substantial load of chemicals (H2O2 and Fe2+) (Vilve

et al. 2010). Thus, in this case for example a use of catalyst or

method combination described in earlier sections could be more

applicable.

The decrease in UV absorbance at 254 nm (UV254) was also

remarkable even when UV radiation without H2O2 was used,

except in the case of washing water (Table 4). When treating 1,2-

DCE containing washing water the UV absorbance at 254 nm

increased.

43

Table 4. Decrease in UV absorbance at 254 nm (cm-1) during 60 min treatments with

UV and UV/H2O2 (decrease in % in parenthesis). *Iron filtered prior to analysis.

Water matrice Initial UV254

(cm-1)

Decrease in UV254 (cm-1)

UV UV + 1.5 mM H2O2

UV + 3 mM H2O2

Chemically coagulated water

0.096 0.041 (43%)

0.081 (85%)

0.084 (88%)

Electrocoagulated water

0.130 0.055 (42%)

0.114 (88%)

0.121 (93%)

Groundwater (PAH contamination)

0.281, 0.130*

0.067 (52%)

0.113 (87%)

0.117 (90%)

Washing water (with 1,2-DCE)

0.612 - - -

Although the removal of TOC from washing water was

rather insignificant, the target pollutant 1,2-DCE was efficiently

oxidized. The removal rates of 45% and 70% were achieved in

the presence of UV + 3mM H2O2 and UV + 6 mM H2O2. Also the

PAH removal in groundwater was efficient. After 60 min

treatment with UV + 3mM H2O2 the concentration of all PAH

compounds were below the detection limit (<0.1 μg/l). Thus, the

aim to remove target pollutants was fulfilled even though the

UV absorption at 254 nm was rather high. Overall, the UV/H2O2

method was suitable in the treatment of pre-coagulated waters

and PAH contaminated groundwater and in case of washing

water, the removal of 1,2-DCE was successful.

The conventional UV light emitting radiation at the

wavelength of about 254 nm was used in this research.

Depending on the water matrix and target compounds some

other emitted wavelengths might be more practical. Thus, novel

radiation sources such as UV LEDs should be taken into account

when planning the use of UV based oxidation methods in water

treatment, especially in larger scale, since the energy savings

compared to conventional UV radiation sources could be

substantial.

44

7 Conclusions and future

perspectives

The AOPs are constantly developing group of methods

applicable for the treatment of various organic compounds in

different water matrices. Also direct photolysis was efficient in

treatment of water contaminated by organic material but

especially in disinfection purposes. Even though the novel

oxidation methods are constantly emerging the use of

conventional AOPs, such as UV/H2O2 and Fenton, is still

extensive. The recent developments involve different factors

such as source of UV radiation, photocatalytic materials and

combination and enhancements of conventional and/or new

processes.

The source of UV radiation is relevant when considering the

treatment and energy efficiency of photochemical and

photocatalytic AOPs. The efficiency of the studied UV LEDs

highly depended on the emitted wavelength (255, 269 and 276

nm) in the treatment of aqueous phenol by UV/H2O2 method.

Long treatment times were necessary since the measured

radiant flux of the LEDs was rather low. Disinfection by direct

photolysis with UV LEDs (269 and 276 nm) was also tested and

LEDs were found to be applicable. However, even though the

UV LED manufacturing process is rather in its development

state, the results showed the promising potential of UV LEDs in

water treatment.

Atomic layer deposited TiO2 films were tested in salicylic

acid degradation with UV radiation. The main result was that

the treatment efficiency depended on the film crystallinity and

the film containing both anatase and rutile phases showed the

highest photocatalytic efficiency. The near neutral pH was the

most effective in destruction of salicylic acid while alkaline

45

medium was better than acidic. ALD proved to be a suitable

method for preparation of photocatalytic TiO2 films.

The applicability of conventional UV/H2O2 method was

tested in treatment of different water matrices. The organic

matter was efficiently removed from the water pretreated with

chemical or electrocoagulation and PAH contaminated

groundwater. Despite the removal of the target pollutant 1,2-

DCE from the washing water from the plant manufacturing ion

exchange resins, the TOC removal was inefficient. However, the

UV absorbance and initial TOC was high in the washing water

compared to the other treated waters. Thus, the properties of the

substances to be treated as well as the water matrix should be

taken into account when planning the use of UV based AOPs

since for example the great UV absorbance of the water might

have major effect on treatment efficiency. Overall, the UV/H2O2

method was applicable in the treatment of pre-coagulated

waters and PAH contaminated groundwater and for the

removal of 1,2-DCE from the washing water.

In further studies, the treatment efficiency of newly

developed UV LEDs should be investigated. With LEDs there

are plenty of interesting aspects like the enormous possibilities

of device structures, because of the compact size of the LED, and

the change for selection of the narrow band wavelength or

multiple wavelengths. Also a critical experimental comparison

of the existing novel UV light sources with similar devices

should be done in order to find out the actual treatment

efficiencies and power consumptions.

Unquestionably the AOPs are furthermore widely researched

and used in water treatment due to their high treatment

efficiencies and multiplicity of the methods. To sum up, few

main future challenges of AOPs in water treatment are the

acquirement of methods for process integration, the usage of

renewable energy sources, the development of low cost

materials to enhance the treatment efficiencies, the targeting at

new groups of pollutants/harmful compounds and the

commercialization of processes which have so far been used in

the laboratory.

46

8 References

Aarik J., Aidla A., Mändar H., Uustare T. (2001): Atomic layer

deposition of titanium dioxide from TiCl4 and H2O: investigation

of growth mechanism. Appl Surf Sci. 172: 148-158.

Adán C., Coronado J.M., Bellod R., Soria J., Yamaoka H. (2006):

Photochemical and photocatalytic degradation of salicylic acid

with hydrogen peroxide over TiO2/SiO2 fibres. Appl Catal A: Gen.

303: 199-206.

Afzal A., Oppenländer T., Bolton J.R., El-Din M.G. (2010): Anatoxin-a

degradation by advanced oxidation processes: Vacuum-UV at 172

nm, photolysis using medium pressure UV and UV/H2O2. Water

Res. 44: 278-286.

Akpan U.G., Hameed B.H. (2009): Parameters affecting the

photocatalytic degradation of dyes using TiO2-based

photocatalysts: A review. J Hazard Mater. 170: 520-529.

Alaton I.A., Balcioglu I.A., Bahnemann D.W. (2002): Advanced

oxidation of a reactive dyebath effluent: comparison of O3,

H2O2/UV-C and TiO2/UV-A processes. Water Res. 36: 1143-1154.

Alnaizy R., Akgerman A. (2000): Advanced oxidation of phenolic

compounds. Adv End Res. 4: 233-244.

Al-Rasheed R.A. (2005): Water treatment by heterogeneous

photocatalysis an overview. 4th SWCC Acquired experience

symposium, Jeddah, Saudi-Arabia.

Amor L., Eiroa M., Kennes C., Veiga M.C. (2005): Phenol

biodegradation and its effect on the nitrification process. Water

Res. 39: 2915-2920.

Ananpattarachai J., Kajitvichyanukul P., Seraphin S. (2009): Visible

light absorption ability and photocatalytic oxidation activity of

various interstitial N-doped TiO2 prepared from different

nitrogen dopants. J Hazard Mater. 168: 253-261.

Anastas, P.T., Warner, J.C.: Green chemistry: Theory and practice. Oxford

University Press, New York, USA, 1998.

Anderson C., Bard A.J. (1997): Improved photocatalytic activity and

characterization of mixed TiO2/SiO2 and TiO2/Al2O3 materials. J

Phys Chem B. 101: 2611-2616.

47

Asano T., Burton F., Leverenz H., Tsuchihashi R., Tchobanoglous G.:

Water reuse. Issues, Technologies and Applications. 1st ed. Inc. Metcalf

and Eddy. McGraw-Hill Companies Inc., New York, USA, 2006

Baum G., Oppenländer T. (1995): Vacuum-UV-oxidation of

chloroorganic compounds in an excimer flow through

photoreactor. Chemosphere. 30: 1781-1790.

Beteta A., Cañizares P., Rodrigo M., Rodríques L., Sáez C. (2009):

Treatment of door-manufacturing factories wastewaters using

CDEO and other AOPs. A comparison. J Hazard Mater. 168: 358-

363.

Bohrerova Z., Shemer H., Lantis R., Impellitteri C., Linden K. (2008):

Comparative disinfection efficiency of pulsed and continuous-

wave UV irradiation technologies. Water Res. 42: 2975-2982.

Bosund M., Aierken A., Tiilikainen J., Hakkarainen T., Lipsanen H.

(2008): Passivation of GaAs surface by atomic-layer-deposited

titanium nitride. Appl Surf Sci. 254: 5385-5389.

Canwell R.E., Hofmann R., Templeton M.R. (2008): Interactions

between humic and bacteria when disinfecting water with UV

light. J Appl Microbiol. 105: 25-35.

Chang C.Y., Yao K.S., Lee J.H., Chen C.H. (2007): Formation and

calculation of hydroxyl radical in the optimal photocatalytic

process using the Taguchi method. Environ Inform Arch. 5: 655-

663.

Chen C., Bai H., Chang S., Chang C., Den W. (2007): Preparation of N-

doped TiO2 photocatalyst by atmospheric pressure plasma

process for VOCs decomposition under UV and visible light

sources. J Nanop Res. 9: 365-375.

Chen D.H., Ye X., Li K. (2005): Oxidation of PCE with a UV LED

photocatalytic reactor. Chem Eng Technol. 28: 95-97.

Chen H.W., Ku Y., Wu C.Y. (2007): Effect of LED optical characteristics

on temporal behavior of o-cresol decomposition bu UV/TiO2

process. J Chem Technol Biotechnol. 82: 626-635.

Chiou C.H., Wu C.Y., Juang R.S. (2008): Photocatalytic degradation of

phenol and m-nitrophenol using irradiated TiO2 in aqueous

solutions. Sep Purif Technol. 62: 559-564.

Comninellis C., Kapalka A., Malato S., Parsons S., Poulios I.,

Mantzavinos D. (2008): Advanced oxidation processes for water

treatment: advances and trends for R&D. J Chem Technol

Biotechnol. 83: 769-776.

Crawford A.H., Banas M.A., Ross M.P., Ruby D.S., Nelson J.S.,

Boucher R., Allerman A.A.: Final LDRD report: Ultraviolet water

48

purification systems for rural environments and mobile applications,

Sandia National Laboratories, Albuquerque, USA, 2005.

Daryany M.K.A., Hosseini S.M., Raie M., Fakharie J., Zareh A. (2009):

Study on continuous (254 nm) and pulsed UV (266 and 355 nm)

lights on BVD virus inactivation and its effects on biological

properties of fetal bovine serum. J Photchem Photobiol B: Biol. 94:

120-124.

De Wildeman S., Linthout G., Van Langenhove H., Verstraete W.

(2004): Complete lab-scale detoxification of groundwater

containing 1,2-dichloroethane. Appl Microbiol Biotechnol. 63: 609-

612.

Dhaouadi A., Monser L., Adhoum N. (2009): Anodic oxidation and

electro-Fenton treatment of rotenone. Electrochim Acta. 54: 4473-

4480.

Diebold U. (2003): The surface science of titanium dioxide. Surf Sci Rep.

48: 53-229.

Dong X., Tao J., Li Y., Zhu H. (2009): Enhanced photoelectrochemical

properties of F-containing TiO2 sphere thin film induced by its

novel hierarchical structure. Appl Surf Sci. 255: 7183-7187.

Epling G.A., Lin C. (2002): Investigation of retardation effects on the

titanium dioxide photodegradation system. Chemosphere. 46: 937-

944.

Eufinger K., Poelman D., Poelman H., De Gryse R., Marin G.B. (2007):

Photocatalytic activity of dc magnetron sputter deposited

amorphous TiO2 thin films. Appl Surf Sci. 254: 148-152.

Ferrari C., Longo I., Tombari E., Bramanti E. (2009): A novel

microwave photochemical reactor for the oxidative

decomposition of Acid Orange 7 azo dye by MW/UV/H2O2

process. J Photochem Photobiol A: Chem. 204: 115-121.

Fox M.A., Dulay M. (1993): Heterogenous photocatalysis. Chem Rev. 93:

341-357.

Fujishima A., Rao T.N., Tryk D.A. (2000): Titanium dioxide

photocatalysis. J Photchem Photobiol C: Photochem Rev. 1: 1-21.

Giri R.R., Ozaki H., Takanami R., Taniguchi S. (2008): A novel use of

TiO2 fiber for photocatalytic ozonation of 2,4-

dichlorophenoxyacetic acid in aqueous solution. J Environ Sci. 20:

1138-1145.

Goldstein S., Aschengrau D., Diamant Y., Rabani J. (2007): Photolysis

of aqueous H2O2: Quantum yield and applications for

polychromatic UV actinometry in photoreactors. Environ Sci

Technol. 41: 7486-7490.

49

Goslan E.H., Gurses F., Banks J., Parsons S.A. (2006): An investigation

into reservoir NOM reduction by UV photolysis and advanced

oxidation processes. Chemosphere. 65: 1113-1119.

Hamamoto A., Mori M., Takahashi A., Nakano M., Wakikawa N.,

Akutagawa M., Ikehara T., Nakaya Y., Kinouchi Y. (2007): New

water disinfection system using UVA light-emitting diodes. J Appl

Microbiol. 103: 2291-2298.

Heikkilä M., Puukilainen E., Ritala M., Leskelä M. (2009): Effect of

thickness of ALD grown TiO2 films on photoelectrocatalysis. J

Photochem Photobiol A: Chem. 204: 200-208.

Hernández-Alonzo M., Fresno F., Suárez S., Coronado J. (2009):

Development of alternative photocatalysts to TiO2: Challenges

and opportunities. Energy Environ Sci. 2: 1231-1257.

Hidaka H., Honjo H., Horikoshi S., Serpone N. (2006): Photocatalyzed

degradation on TiO2-coated quartz crystal microbalance.

Adsorption/desorption processes in real time in the degradation

of benzoic acid and salicylic acid. Catal Comm. 7: 331-335.

Hoffmann M., Martin S., Choi W., Bahnemann D. (1995):

Environmental applications of semiconductor photocatalysis.

Chem Rev. 95: 69-96.

Hong J., Ta N., Yang S., Liu Y., Sun C. (2007): Microwave assisted

direct photolysis of bromophenol blue using electrodeless

discharge lamps. Desalination. 214: 62-69.

Horikoshi S., Hidaka H., Serpone N. (2004): Environmental

remediation by an integrated microwave/UV illumination

technique VI. A simple modified domestic microwave oven

integrating an electrodeless UV-Vis lamp to photodegrade

environmental pollutants in aqueous media. J Photochem Photobiol

A: Chem. 161: 221-225.

Horikoshi S., Hidaka H., Serpone N. (2003): Environmental

remediation by an integrated microwave/UV-illumination

technique IV. Non-thermal effects in the microwave-assisted

degradation of 2,4-dichlorophenoxyacetic acid in UV-irradiated

TiO2/H2O dispersion. J Photochem Photobiol A: Chem. 159: 289-300.

Horikoshi S., Hidaka H., Serpone N. (2002a): Environmental

remediation by an integrated microwave/UV illumination

technique. 3. A microwave-powered plasma light source and

photoreactor to degrade pollutants in aqueous dispersions of TiO2

illuminated by the emitted UV/visible radiation. Environ Sci

Technol. 36: 5229-5237.

Horikoshi S., Hidaka H., Serpone N. (2002b): Environmental

remediation by an integrated microwave/UV-illumination

50

method II. Characteristics of a novel UV–VIS–microwave

integrated irradiation device in photodegradation processes. J

Photochem Photobiol A: Chem. 153: 185-189.

Horikoshi S., Kajitani M., Sato S., Serpone N. (2007): A novel

environmental risk-freemicrowave discharge electrodeless lamp

(MDEL) in advanced oxidation processes. Degradation of the 2,4-

D herbicide. J Photochem Photobiol A: Chem. 189: 355-363.

Houas A., Lachheb H., Ksibi M., Elaloui E., Guillard C., Herrmann J.-.

(2001): Photocatalytic degradation pathway of methylene blue in

water. Appl Catal B: Env. 31: 145-157.

Hu X., Deng J., Zhang J.P., Lunev A., Bilenko Y., Katona T., Shur M.S.,

Gaska R., Shatalov M., Khan A. (2006): Deep ultraviolet light-

emitting diodes. Phys stat sol. 203: 1815-1818.

Huang Y.F., Huang Y.H. (2009): Identification of produced powerful

radicals involved in the mineralization of bisphenol A using a

novel UV-Na2S2O8/H2O2-Fe(II,III) two-stage oxidation process. J

Hazard Mater. 162: 1211-1216.

Hurum D.C., Agrios A.G., Gray K.A., Rajh T., Thurnauer M.C. (2003):

Explaining the enhanced photocatalytic activity of Degussa P25

mixed-phase TiO2 using EPR. J Phys Chem B. 107: 4545-4549.

Ikematsu T., Hayashi N., Ihara S., Satoh S., Yamabe C. (2004):

Advanced oxidation processes (AOPs) assisted by excimer lamp.

Vacuum. 73: 579-582.

Kansal S.K., Singh M., Sud D. (2007): Studies on photodegradation of

two commercial dyes in aqueous phase using different

photocatalysts. J Hazard Mater. 141: 581-590.

Karunakaran C., Senthilvelan S. (2005): Photocatalysis with ZrO2:

oxidation of aniline. J Molec Catal A: Chem. 233: 1-8.

Kemell M., Pore V., Tupala J., Ritala M., Leskelä M. (2007): Atomic

layer deposition of nanostructured TiO2 photocatalysis via

template approach. Chem Mater. 19: 1816-1820.

Khan M.A. (2006): AlGaN multiple quantum well based deep UV

LEDs and their applications. Phys stat sol. 203: 1764-1770.

Koparal A.S., Yildiz Y.Ş., Keskinler B., Demircioğlu N. (2008): Effect of

initial pH on the removal of humic substances from wastewater

by electrocoagulation. Sep Pur Technol. 59: 175-182.

Kusic H., Koprivanac N., Bozic A.L. (2006a): Minimization of organic

pollutant content in aqueous solution by means of AOPs: UV- and

ozone-based technologies. Chem Env J. 123: 127-137.

Kusic H., Koprivanac N., Bozic A.L., Selanec I. (2006b): Photo-assisted

Fenton type processes for the degradation of phenol: A kinetic

study. J Hazard Mater. B136: 632-644.

51

Langlet M., Permpoon S., Riassetto D., Berthomé G., Pernot E., Joud

J.C. (2006): Photocatalytic activity and photo-induced

superhydrophilicity of sol-gel derived TiO2 films. J Photochem

Photobiol A: Chem. 181: 203-214.

Lee C., Sedlak D. (2009): A novel homogeneous Fenton-like system

with Fe(III)-phosphotungstate for oxidation of organic

compounds at neutral pH values. J Molec Catal A: Chem. 311: 1-6.

Lee H., Hur T., Kim S., Kim J., Lee H. (2003): Effects of pH and surface

modification of TiO2 with SiOx on the photocatalytic degradation

of a pyrimidine derivative. Catal Today. 84: 173-180.

Legrini O., Oliveros E., Braun A.M. (1993): Photochemical processes

for water treatment. Chemical Reviews. 93: 671-698.

Li C.H., Hsieh Y.H., Chiu W.T., Liu C.C., Kao C.L. (2007): Study on

preparation and photocatalytic performance of Ag/TiO2 and

Pt/TiO2 photocatalysts. Sep Purif Technol. 58: 148-151.

Li Q.R., Gu C.Z., Di Y., Yin H., Zhang J.Y. (2006): Photodegradation of

nitrobenzene using 172 nm excimer UV lamp. J Hazard Mater.

B133: 68-74.

Li X.Y., Cui Y.H., Feng Y.J., Xie Z.M., Gu J.D. (2005): Reaction

pathways and mechanisms of the electrochemical degradation of

phenol on different electrodes. Water Res. 39: 1972-1981.

Lim G.T., Kim D. (2006): Characteristics of TiOx films prepared by

chemical vapor deposition using tetrakis-dimethyl-amido-

titanium and water. Thin Solid Films. 498: 254-258.

Maehara T., Miyamoto I., Kurokawa K., Hashimoto Y., Iwamae A.,

Kuramoto M., Yamashita H., Mukasa S., Toyota H., Nomura S.,

Kawashima A. (2008): Degradation of methylene blue by RF

plasma in water. Plasma Chem Plasma Process. 28: 467-482.

Maehara T., Nishiyama K., Onishi S., Mukasa S., Toyota H., Kuramoto

M., Nomura S., Kawashima A. (2010): Degradation of methylene

blue by radio frequency plasmas in water under ultraviolet

irradiation. J Hazard Mater. 174: 473-476.

Mahamuni N.N., Adewuyi Y.G. (2009): Advanced oxidation processes

(AOPs) involving ultrasound for waste water treatment: A review

with emphasis on cost estimation. Ultrasonics Sonochem. In Press.

Mantzavinos D., Psillakis E. (2004): Enhancement of biodegradability

of industrial wastewaters by chemical oxidation pre-treatment. J

Chem Technol Biotechnol. 79: 431-454.

Martínez F., Calleja G., Melero J., Molina R. (2005): Heterogeneous

photo-Fenton degradation of phenolic aqueous solutions over

iron-containing SBA-15 catalyst. Appl Catal B: Environ. 60: 181-190.

52

Matilainen A., Sillanpää M. (2010): Removal of natural organic matter

from drinking water by advanced oxidation processes: A review.

Chemosphere. In Press.

McCullagh C., Robertson J., Bahnemann D., Robertson P. (2007): The

application of TiO2 photocatalysis for disinfection of water

contaminated with pathogenic micro-organisms: a review. Res

Chem Intermed. 33: 359-375.

Méndez-Arriaga F., Torres-Palma R.A., Pétrier C., Esplugas S.,

Gimenez J., Pulgarin C. (2009): Mineralization enhancement of a

recalcitrant pharmaceutical pollutant in water by advanced

oxidation hybrid process. Water Res. 43: 3948-3991.

Mills A., Le Hunte S. (1997): An overview of semiconductor

photocatalysis. J Photochem Photobiol A: Chem. 108: 1-35.

Mills A., Lepre A., Elliot N., Bhopal S., Parkin I.P., O'Neill S.A. (2003):

Characterization of the photocatalyst Pilkington ActivTM: a

reference film photocatalyst? J Photobiol Photochem. 160: 213-224.

Momani F.A., Sans C., Esplugas S. (2004): A comparative study of the

advanced oxidation of 2,4-dichlorophenol. J Hazard Mater. B107:

123-129.

Mudliar R., Umare S.S., Ramteke D.S., Wate S.R. (2009): Energy

efficient-Advanced oxidation process for treatment of cyanide

containing automobile industry wastewater. J Hazard Mater. 164:

1474-1479.

Naunovic Z., Lim S., Blatchley E.R. (2008): Investigation of microbial

inactivation efficiency of a UV disinfection system employing an

excimer lamp. Water Res. 42: 4838-4846.

Nurizzo C., Antonelli M., Profaizer M., Romele L. (2005): By-products

in surface and reclaimed water disinfected with various agents.

Desalination. 176: 241-253.

Ohno K., Sarukawa K., Tokieda K., Matsumura M. (2001): Morphology

of TiO2 photocatalyst (Degussa, P-25) consisting of anatase and

rutile crystalline phases. J Catal. 203: 82-86.

Oppenländer T., Walddörfer C., Burgbacher J., Kiermeier M., Lachner

K., Weinschrott H. (2005): Improved vacuum-UV (VUV)-initiated

photomineralization of organic compounds in water with a xenon

excimer flow-through photoreactor (Xe2* lamp, 172 nm)

containing an axially centered ceramic oxygenator. Chemosphere.

60: 302-309.

Patil K.R., Sathaye S.D., Khollam Y.B., Deshpande S.B., Pawaskar N.R.,

Mandale A.B. (2003): Preparation of TiO2 thin films by modified

spin-coating method using an aqueous precursor. Mater Lett. 57:

1775-1780.

53

Pore V., Heikkilä M., Ritala M., Leskelä M., Areva S. (2006): Atomic

layer deposition of TiO2-xNx thin films for photocatalytic

applications. J Photochem Photobiol A: Chem. 177: 68-75.

Pore V., Rahtu A., Leskelä M., Ritala M., Sajavaara T., Keinonen J.

(2004): Atomic layer deposition of photocatalytic TiO2 thin films

from titanium tetramehoxide and water. Chem Vapor Deposition.

10: 143-148.

Pore V., Ritala M., Leskelä M., Areva S., Järn M., Järnström J. (2007):

H2S modified atomic layer deposition process for photocatalytic

TiO2 thin films. J Mater Chem. 17: 1361-1371.

Poupopoulos S.G., Arvanitakis F., Philippopoulos C.J. (2006):

Photochemical treatment of phenol aqueous solutions using

ultraviolet radiation and hydrogen peroxide. J Hazard Mater. B129:

64-68.

Prabakar K., Takahashi T., Nezuka T., Takahashi K., Nakashima T.,

Kubota Y., Fujishima A. (2008): Visible light-active nitrigen-doped

TiO2 thin films prepared by DC magnetron sputtering used as a

photocatalyst. Renew Energy. 33: 277-281.

Pradhan A., Gogate P. (2010): Degradation of p-nitrophenol using

acoustic cavitation and Fenton chemistry. J Hazard Mater. 173: 517-

522.

Prasannakumar B., Regupathib I., Murugesan T. (2009): An

optimization study on microwave irradiated decomposition of

phenol in the presence of H2O2. J Chem Technol Biotechnol. 84: 83-

91.

Rehman S., Ullah R., Butt A., Gohar N. (2009): Strategies of making

TiO2 and ZnO visible light active. J Hazard Mater. 170: 560-569.

Rosenfeldt E.J., Linden K.G. (2004): Degradation of endocrine

disrupting chemicals bisphenol A, ethinyl estradiol and estradiol

during UV photolysis and advanced oxidation processes. Environ

Sci Technol. 38: 5476-5483.

Salokannel A., Heikkinen J., Kumpulainen M., Sillanpää M., Turunen J.

(2007): Tertiary treatment of pulp and paper mill wastewaters by

ozonation and O3/H2O2. Paper and Timber. 89: 348-351.

Salovsky P., Shopova V., Danecheva V., Yordanov Y., Marinov E.

(2002): Early pneumotoxic effects after oral administration of 1,2-

dichloroethane. J Occup Environ Med. 44: 475-480.

Schaefer R., Grapperhaus M., Schaefer I., Linden K. (2007): Pulsed UV

lamp performance and comparison with UV mercury lamps. J

Environ Eng Sci. 6: 303-310.

Schrank S.G., dos Santos, J. N. R., Souza D.S., Souza E.E.S. (2007):

Decolourisation effects of Vat Green 01 textile dye and textile

54

wastewater using H2O2/UV process. J Photochem Photobiol A: Chem.

186: 125-129.

Segura Y., Molina R., Martínez F., Melero J.A. (2009): Integrated

heterogeneous sono-photo Fenton processes for the degradation

of phenolic aqueous solution. Ultrasonics Sonochem. 16: 417-424.

Shemer H., Linden K.G. (2007): Aqueous photodegradation and

toxicity of the polycyclic aromatic hydrocarbons fluorene,

dibenzofuran, and dibenzothiophene. Water Res. 41: 853-861.

Shie J.L., Lee C.H., Chiou C.S., Chang C.T., Chang C.C., Chang C.Y.

(2008): Photodegradation kinetics of formaldehyde using light

sources of UVA, UVC and UVLED in the presence of composed

silver titanium dioxide photocatalyst. J Hazard Mater. 155: 164-172.

Soloshenko I.A., Bazhenov V.Y., Khomich V.A., Tsiolko V.V.,

Potapchenko N.G. (2006): Comparative research of efficiency of

water decontamination by UV radiation of cold hollow cathode

discharge plasma versus that of low- and medium-pressure

mercury lamps. IEEE Trans Plasma Sci. 34: 1365-1369.

Songwang Y., Gao L. (2008): Photocatalytic activity of nitrogen doped

rutile TiO2 nanoparticles under visible light irradiation. Mater Res

Bullet. 43: 1872-1876.

Taniyasu Y., Kasu M., Makimoto T. (2006): An aluminum nitride light-

emitting diode with a wavelength of 210 nm. Nature. 441: 325-328.

Tchobanoglous G., Burton F.L., Burton F., Stensel H.D.: Wastewater

Engineering: Treatment and Reuse, 4th ed., Inc. Metcalf and Eddy,

McGraw-Hill Companies Inc., New York, USA, 2005.

Tunesi S., Anderson M. (1991): Influence of chemisorption on the

photodecomposition of salicylic acid and related compounds

using suspended TiO2 ceramic membranes. J Phys Chem. 95: 3399-

3405.

Vepsäläinen M., Ghiaswand A., Selin J., Pienimaa J., Kukkamäki E.,

Pulliainen M., Sillanpää M. (2009): Investigations of the effects of

temperature and initial sample pH on natural organic matter

(NOM) removal with electrocoagulation using response surface

method (RSM). Sep Purif Technol. 69: 255-261.

Vilve M., Hirvonen A., Sillanpää M. (2007): Ozone-based advanced

oxidation processes in nuclear laundry water treatment. Environ

Technol. 28: 961-968.

Vilve M., Vilhunen S., Vepsäläinen M., Kurniawan T., Lehtonen N.,

Isomäki H., Sillanpää M. (2010): Degradation of 1,2-

dichloroethane from wash water of ion-exhange resin using

Fenton's oxidation. Environ Sci Pollut Res. In Press.

55

Vogelpohl A. (2007): Applications of AOPs in wastewater treatment.

Water Sci Technol. 55: 207-211.

Walling C. (1975): Fenton's reagent revisited. Acc Chem Res. 8: 125-131.

Wang G.S., Hsieh S.T., Hong C.S. (2000): Destruction of humic acid in

water by UV light-catalyzed oxidation with hydrogen peroxide.

Water Res. 34: 3882-3887.

Wang W.Y., Ku Y. (2006): Photocatalytic degradation of Reactive Red

22 in aqueous solution by UV-LED radiation. Water Res. 40: 2249-

2258.

Wu P.G., Ma C.H., Shang J.K. (2005): Effects of nitrogen doping on

optical properties of TiO2 thin film. Appl Phys A. 81: 1411-1417.

Yildiz Y.Ş., Koparal A.S., İrdemez Ş., Keskinler B. (2007):

Electrocoagulation of synthetically prepared waters containing

high concentration of NOM using iron cast electrodes. J Hazard

Mater. B139: 373-380.

Yu J.C., Yu J., Zhao J. (2002): Enhanced photocatalytic activity of

mesoporous and ordinary TiO2 thin films by sulfuric acid

treatment. Appl Catal B: Env. 36: 31-43.

Zhang J.Y., Boyd I.W. (2000): Lifetime investigation of of excimer UV

sources. Appl Surf Sci. 168: 296-299.

Zhang X., Pan J.H., Du A.J., Fu W., Sun D.D., Leckie J.O. (2009):

Combination of one-dimensional TiO2 nanowire photocatalytic

oxidation with microfiltration for water treatment. Water Res. 43:

1179-1186.

Zhao L., Jiang Q., Lian J. (2008a): Visible-light photocatalytic activity of

nitrogen-doped TiO2 thin film prepared by pulsed laser

deposition. Appl Surf Sci. 254: 4620-4625.

Zhao Y., Li C., Liu X., Gu F., Du H.L., Shi L. (2008b): Zn-doped TiO2

nanoparticles with high photocatalytic activity synthesized by

hydrogen-oxygen diffusion flame. Appl Catal B: Env. 79: 208-215.

Zhou T., Lu X., Wang J., Wong F.S., Li Y. (2009): Rapid decolorization

and mineralization of simulated textile wastewater in a

heterogeneous Fenton like system with/without external energy. J

Hazard Mater. 165: 193-199.

Zhu J., Zheng W., He B., Zhang J., Anpo M. (2004): Characterization of

Fe-TiO2 photocatalysts synthesized by hydrothermal method and

their photocatalytic reactivity for photodegradation of XRG dye

diluted in water. J Molec Catal A: Chem. 216: 35-43.

Zhu X., Ni J., Lai P. (2009): Advanced treatment of biologically

pretreated coking wastewater by electrochemical oxidation using

boron doped diamond electrodes. Water Res. 43: 4347-4355.

Publications of the University of Eastern FinlandDissertations in Forestry and Natural Sciences



isbn 978-�952-�61-�0183�-�5

Sari Vilhunen

UVC Irradiation Based Water TreatmentA Study of UV Light Emitting Diodes, Atomic


UVC irradiation based water treat-

ment techniques presented in this

doctoral dissertation belong to a

wide group of Advanced Oxidation

Processes (AOPs). Even though AOPs

are extensively used and studied for

decades, novel approaches appear

constantly. The increasing need for

water treatment caused by e.g. the

rapidly broadening industrializa-

tion, population growth and the

awareness of the disadvantages of

many pollutants have urged for the

development of energy efficient and

environmentally sustainable water

treatment techniques. This doctoral

dissertation introduces the latest

material and methods in the field of

UV irradiation based AOPs.

dissertatio

ns | 013 | S

ar

i Vilh

un

en | U

VC

Irrad

iatio

n B

ased

Wa

ter Trea

tmen

t - A S

tud

y of UV

Ligh

t Em

itting D

iod

es...

Sari VilhunenUVC Irradiation Based

Water TreatmentA Study of UV Light Emitting Diodes, Atomic


| 013 | sari vilhunen | sari vilhunen uvc irradiation ...fi-50100 mikkeli, finland e-mail:...

Documents