Journal of Environmental Chemical Engineering 1 (2013) 183–188

Efficacy of electrocoagulation and electrooxidation for the purification ofwastewater generated from gelatin production plant

N. Lakshmi Kruthika, S. Karthika, G. Bhaskar Raju *, S. Prabhakar

National Metallurgical Laboratory Madras Centre, CSIR Madras Complex, Taramani, Chennai 600113, India

A R T I C L E I N F O

Article history:

Received 6 February 2013

Accepted 24 April 2013

Keywords:

Electrocoagulation

Electrooxidation

MMO electrode

TiO2 nanotubes

Purification

Electrode scaling

A B S T R A C T

The effluents of gelatin production plant are highly complex and difficult to treat by conventional

methods. The electrochemical techniques involving electrocoagulation and electrooxidation were

attempted for the treatment of wastewater from gelatin production plant. Around 60% of TOC removal

was achieved by electrocoagulation using aluminum as anode. However, the performance was severely

affected due to scaling of the electrodes. The high concentration of dissolved calcium was found to be

responsible for scaling of electrodes. To minimize the scaling, calcium was precipitated as CaCO3 using

bicarbonate. After the calcium was precipitated, scaling was reduced and the performance of the

electrodes was drastically improved. The effect of applied current density and flow rate on TOC removal

was studied and the energy consumption for electrocoagulation was estimated. Since the removal of

pollutants by electrocoagulation is only partial, the wastewater was processed further by

electrooxidation using IrO2–Ta2O5 coated Ti electrode and TiO2 nanotubes grown on titanium sheet

(TiO2 NT) as electrodes. The TOC removal was drastically improved in the presence of TiO2 NT electrode.

� 2013 Elsevier Ltd All rights reserved.

Contents lists available at SciVerse ScienceDirect

Journal of Environmental Chemical Engineering

jou r n al h o mep ag e: w ww .e lsev ier . co m / loc ate / jec e

Introduction

Gelatin is a heterogeneous mixture of proteins derived from thecollagen of animal hide and bone. It is commonly used in industriessuch as food, pharmaceuticals, photography, cosmetics and winefining [1]. The process of gelatin production from bones includesvariety of unit operations such as acidulation, liming, washing,extraction, filtration, deionization, evaporation, sterilization,drying and blending. During de-mineralization of bone chips, di-calcium phosphate is produced as byproduct. The initial concen-tration of gel in extracted gelatin solutions is typically 5% and thesame is enriched to 30% by multi-stage vacuum evaporator. Theconcentrated, purified gelatin solution is then sterilized at 140 8Cfor bacterial control. The dried gel with 11–12% of moisture isground to coarse granules and packed. During the process,approximately 300 m3 of wastewater is generated for each metricton of bones processed. It was reported that the waste generatedfrom gelatin industry is rich in nitrogen, calcium and phosphorus[2]. However, the odor is highly obnoxious and nuisance to thehabitation. The vermiculture based technology was suggested totreat wastewater from gelatin production unit [3]. The bench scalestudy revealed that around 87% of COD removal could be achieved

* Corresponding author. Tel.: +91 44 22542077; fax: +91 44 22541027.

E-mail addresses: gbraju55@gmail.com, GBRAJU55@HOTMAIL.COM

(G. Bhaskar Raju).

2213-3437/$ – see front matter � 2013 Elsevier Ltd All rights reserved.

http://dx.doi.org/10.1016/j.jece.2013.04.017

in 16 h [4] by activated sludge aeration process. Since most of thesuspended solids are partially hydrophobic, the settling behaviorof suspended solids would be very slow by coagulation. In recentyears, zero discharge norms were imposed to restrict the dischargeof wastewater in to the environment. The recycling of the treatedwastewater is being enforced to minimize the percolation ofcontaminants to groundwater and to save the water resources.Hence, electrochemical techniques were explored to treat waste-water from gelatin production plant.

In recent years, electrochemical techniques are gaining impor-tance for the treatment of wastewater containing dyes [5,6],tannins [7], hexavalent chromium [8] and phenols [9]. The efficacyof electrochemical techniques for the purification of industrialwastewater containing variety of pollutants was reported to betremendous [10–12]. The principles of electrocoagulation andelectrooxidation technologies, design of electrochemical reactorswas extensively reviewed and reported by Chen [13]. In thepresent work, the efficacy of electrocoagulation and electrooxida-tion for the treatment of effluents generated from gelatinproduction plant was reported.

Materials and methods

Electrochemical reactors

Electrocoagulation reactor with a working volume of 1.0 L wasfabricated using acrylic material. It is a continuous type reactor

Fig. 1. (a) Electrocoagulation reactor (1 and 2: electrodes; 3: magnetic stirrer; 4:

magnetic paddle; 5: thermometer) and (b) electrooxidation reactor (1 and 2:

electrodes; 3: magnetic stirrer; 4: magnetic paddle; 5: thermometer).

Fig. 2. High resolution scanning electron micrograph of TiO2 nanotubes.

N. Lakshmi Kruthika et al. / Journal of Environmental Chemical Engineering 1 (2013) 183–188184

with an inlet at the bottom and outlet at top of the reactor as shownin Fig. 1a. The contents in the reactor are kept under agitation usinga magnetic stirrer. Stainless steel 316 and aluminum rods with aminimum purity of 98% and measuring 1.2 cm diameter and 8 cmlength were used as electrodes. The anode and cathode wereimmersed in wastewater vertically. The gap between the electro-des was maintained at 1.0 cm. The surface area of cathode andanode was estimated to be 35.04 cm2 and 31.27 cm2 respectively.The electrolysis was carried out under galvanostatic conditions.The schematic diagram of experimental set-up is shown in Fig. 1a.The coagulated sample was allowed to settle for half an hour beforethe supernatant solution was analyzed for TOC.

Electro oxidation was performed in a batch type reactor with aworking volume of 0.350 L. All the experiments were conducted ata constant temperature of 25 8C with the help of water bath. Anarray of TiO2 nanotubes grown on titanium sheet was used asanode and platinum foil as cathode for electrooxidation. Thesurface area of the titanium electrode covered with nanotubes is4.0 cm2. In the case of electrooxidation, the electrodes wereseparated by 0.5 cm.

Electrodes were connected to the respective terminals of the DCrectifier and energized for a required duration at a known currentdensity. Potentiostat/galvanostat system (Model-KM064, K-PasInstronics Engineers, India) with digital indicators was used as DCsource. The schematic diagram of experimental set-up is shown inFig. 1b. The kinetics of TOC removal during the experiment wasascertained by TOC measurements.

Preparation of Ti nanotubes electrode

The TiO2-nanotube array grown on Ti sheet by anodizationmethod [14] was used as anode for electrooxidation. The titaniumsheets measuring 0.2 cm thick 2.0 cm breadth and 2.0 cm lengthwere initially mirror polished and then ultrasonically de-greased.These sheets were anodized in the presence of 95% ethylene glycol(99% purity) and 0.025 M sodium fluoride electrolyte. Theanodization was continued for a period of 6 h at 20 V. Afteranodization, the samples were washed with water and ultra-sonicated in acetone to remove surface debris. The anodizedamorphous TiO2 nanotubes were annealed at 480 8C in oxygenatmosphere for 6 h with heating and cooling rate of 1 8C min�1 toobtain crystallized samples. The morphology and array ofnanotubes are presented in Fig. 2. The SEM images indicate thatthe average diameter and wall thickness of the nanotubes isaround 80 nm and 15 nm respectively. The height/length of eachtube is observed to be more than 500 nm. From SEM–EDAX data,the weight percentage of O, Ti and Ta was found to be 34.23, 63.23and 1.96, respectively.

Analytical techniques

The aqueous solutions were analyzed for dissolved solids,turbidity, water hardness, etc. according to the standard methodssuggested by American Public Health Association [15]. For TOCanalysis, all the samples were kept for 1 h to allow particles tosettle. The supernatant solution was siphoned out and subjected toTOC analyzer (Shimadzu VCSN/CPN Model). The homogenizedsample was injected in to reaction chamber packed with catalyst.The carbon is oxidized to CO2 in the presence of catalyst and thisgas is quantitatively estimated by non-dispersive infrared analyz-er. The TOC was deduced from the measurements of total carbonand inorganic carbon.

Effluent sample

Portion of the wastewater sample from the main line wascollected intermittently over a period of 12 h. The wastewatersample thus collected was uniformly mixed and stored in a plasticdrum. The representative sample was analyzed for variousparameters and the characteristics of the same are presented inTable 1. The results indicate that the concentration of totaldissolved solids (TDS) is 55 g L�1 and consequently the conductiv-ity of wastewater is also high. The chloride (34 g) and calcium(17.6 g) resulted due to neutralization of acidic wastewater by limeare the major contributors of TDS. The total organic carbon (TOC)was estimated to be 200 ppm. The high alkalinity and turbidity wasdue to the presence of colloidal size lime particles.

Results and discussion

Electrocoagulation

Laboratory scale and continuous type electrocoagulationexperiments were conducted at different current densities usingaluminum electrodes. The effective surface area of electrodes wasuniformly maintained at 31.27 cm2 in all the experiments. Theremoval of TOC over a period of 9 h was studied and the results arepresented in Table 2. It is apparent that the TOC removal variesfrom 38% to 54% depending on the applied current but not on

Table 1Characteristics of raw effluent.

S. no. Parameters Results

1 Appearance Turbid

2 pH value at 25 8C 5.90

3 Color (Hazen unit) 25 Hu

4 Odour Objectionable

5 Turbidity as NTU NTU

6 Electrical conductivity at 25 8C 600 mV/cm

7 Phenolphthaline alkalinity as CaCO3 Nil

8 Total alkalinity as CaCO3 1020 ppm

9 Total hardness as CaCO3 44,481 ppm

10 Calcium hardness as CaCO3 44,044 ppm

11 Calcium as Ca2+ 17,618 ppm

12 Magnesium hardness as MgCO3 437 ppm

13 Magnesium as Mg2+ 104.9 ppm

14 Total suspended solids 168 ppm

15 Total dissolved solids 54,984 ppm

16 Chlorine as Cl� 34,083 ppm

17 Sulphur as SO42� 11.54 ppm

18 Total iron 1.59 ppm

19 Silica (reactive) as SiO2 68.6 ppm

20 Carbonate hardness 1020 ppm

21 Non-carbonate hardness 43,461 ppm

22 Free residual chlorine <0.2 ppm

23 TOC 194 ppm

24 COD 1280 ppm

25 BOD at 27 8C for 3 days 284 ppm

N. Lakshmi Kruthika et al. / Journal of Environmental Chemical Engineering 1 (2013) 183–188 185

electrode geometry. It was observed that the dissolution isprominent at the edges and corners of the electrode. The hexagonalrod has slowly become cylindrical within first 1 h of electrolysis. Thepreferential dissolution of edges and corners may be attributed dueto high stress and the presence of active centers. It is known fromFaraday’s laws that by increasing the current, the dissolution ofanode increases irrespective of the electrode geometry. Accordinglycoagulation of suspended solids was also increased and thereby theTOC removal. Conversely, Keithley 2182 a nanovolt meter hasindicated increase in resistivity and as a result the temperature of thewastewater was increased to 50 8C during electrolysis. Theexamination of electrodes has revealed that the cathode surfacewas coated with white solid. When the aluminum cathode wasreplaced by stainless steel 316 rod, the problem of coating wasdrastically improved and the TOC removal was increased to 68%.Thus, the performance of SS 316 was found to be better cathode toimprove the TOC removal without scaling problems. Electrocoagu-lation was conducted at an applied current density of 12.6 mA cm�2

and flow rate of 1.0 L/h using aluminum rods as anode.The anodic dissolution of aluminum can be represented as:

Anode : 2Al0 ! 2Al3þ þ 6e� (1)

Cathode : 6H2O þ 6e� ! 3H2þ 6OH� (2)

Net reaction:

2Al þ 6H2O ! 2AlðOHÞ3þ 3H2ðbasic conditionÞ (3)

Table 2Effect of electrode material and geometry on TOC removal (sample: as received,

duration of experiment: 9 h, flow rate: 1.0 L/h.

Cathode Anode Current

density

(mA/cm2)

TOC

removal

(%)

Resistivity (mV)

Cathode Anode

Al rod Al rod 31.98 54.65 0.3572 0.4402

Al rod Al rod 12.79 49.89 0.2697 0.2964

Al rod Al rod 6.40 38.43 0.2647 0.2834

Al rod

(hexagonal)

Al rod

(hexagonal)

12.79 50.72 0.3409 0.3425

SS rod Al rod 12.79 68.37

2Al þ 6H2O ! 2AlðOHÞ3þ 6Hþðacidic conditionÞ (4)

It is known that depending on the pH of aqueous solution, Al3+

could result in the formation of mono and poly nuclear complexes/species such as AlOH2+, Al(OH)2

+, Al(OH)3, Al(OH)4�, Al(OH)n

(3�n),Al2(OH)2

4+, Al7(OH)174+, Al13(OH)34

5+, Al3(OH)45+, Al(OH)6

3� withdifferent charge. In addition to anodic dissolution, Al3+ ions arereleased from the surface due to corrosion and pH of the aqueoussolution (chemical dissolution). At high pH values, preferentialdissolution of the protective oxide layer (boehmite) was suggestedas per the following reaction [16].

AlOOH þ OH� ! AlO2� þ H2O (5)

The dissolved metal ions and metal oxy-hydroxides aid thecoagulation of suspended solids. It is generally accepted thatcoagulation of suspended solids is brought about primarily byreduction of net surface charge to a point where they hold togetherby inter molecular Vander Waals forces. The resistivity of theelectrodes was measured before and after electrocoagulation. Theresistivity of original aluminum cylindrical rod and hexagonal rodbefore using them for electrocoagulation was measured to be0.3774 mV and 0.3385 mV, respectively. After 9 h of electro-coagulation, the resistivity of these electrodes was found toincrease at higher applied current of above 400 mA. This behaviorcould be explained due to the formation of Al2O3 film at theelectrode surface which is non-conductive [17]. Despite theresistivity is less than the original sample at low current densities,the coating of white substance on the electrodes was observed. Thedecrease in resistivity may be explained due to formation ofconductive film on the electrode surface. The photograph revealingthe scaling of electrodes is shown in Fig. 3. The coated material wasscrapped from the surface and analyzed for its chemical assay. Theresults revealed that CaCl2 is the major compound. The coating ofCaCl2 is obvious when the wastewater contain 17.6 g of Ca2+ and34 g of Cl� per liter. At very high concentrations, the electropho-retic mobility of conductive ions towards the electrode maydominate the process of anodic dissolution of metal. In other

Fig. 3. Scaling of aluminum electrodes of different geometries after 6 h of

electrolysis.

0 5 10 15 20 250

10

20

30

40

50

60

70

Flow rate

TO

C r

em

oval %

Time ( h)

1 L /h

5 L /h

7 L /h

Fig. 5. Effect of flow rate/residence time on TOC removal (current density:

12.6 mA cm�2).

N. Lakshmi Kruthika et al. / Journal of Environmental Chemical Engineering 1 (2013) 183–188186

words, the rate of Al3+ dissolution is less than the rate of diffusionof dissolved Ca2+ and Cl� to the electrode surface. Hence, thedissolved ions from the solution are deposited on the electrodesurface. It clearly suggests that the performance of the electrodeswill be drastically affected at high concentration of dissolved ions.

Since Ca2+ was found to be responsible for scaling, the same wasprecipitated using bicarbonate. The precipitation of CaCO3 can berepresented as

2NaHCO3þ CaCl2 ! 2NaCl þ CaCO3þ CO2þ H2O (6)

The supernatant liquid was collected in bulk and the Ca2+ wasfound to be decreased to 0.09 M. This wastewater was used forfurther electrocoagulation tests.

Effect of applied current density

Current density is the key design parameter that has directbearing on electrical energy of the process. The effect of currentdensity on TOC removal was studied at three different appliedcurrent densities viz. 12.6, 22.39 and 31.98 mA cm�2 at a flow rateof 1.0 L/h. All the experiments were conducted using SS 316 ascathode and Al as anode. Samples were collected at regularintervals over a period of 24 h and the results obtained are plottedin Fig. 4. From the results, it is apparent that the influence ofapplied current density on TOC removal was observed only atinitial stage. The difference is very marginal beyond 10 helectrolysis. In all the cases, the maximum removal was observedto be around 65%. It is known that the power consumption isproportional to applied current density. The power consumptionwas estimated to be 0.63 Wh/L, 1.64 Wh/L, 2.44 Wh/L for currentdensities of 12.6, 22.39 and 31.98 mA cm�2 respectively. Hence thecurrent density was limited to 12.6 mA cm�2.

Effect of flow rate

Electrocoagulation experiments were conducted at differentflow rates corresponding to the retention times of 3600, 720 and513 s and at a constant current density of 12.6 mA cm�2. The TOCremoval as a function of flow rate is presented in Fig. 5. The TOCremoval was observed to be 65%, 41% and 37% at the respectiveflow rates of 1.0 L/h, 5.0 L/h and 7.0 L/h. The decrease in removalwith increasing flow rate could be interpreted due to less residencetime and thereby less coagulant dosage. Though the removalpercentage is nearly half at the flow rate of 7.0 L/h, the energy

0 5 10 15 20 25

0

20

40

60

TO

C r

em

oval %

Time (h)

12.6 mAcm-2

22.39 mAcm-2

31.98 mAcm-2

Fig. 4. Effect of current density on TOC removal (flow rate: 1.0 L/h, cathode: SS 316,

anode: aluminum).

consumption is drastically reduced from 0.63 Wh/L to 0.09 Wh/L.Since the removal of TOC at higher flow rate is only partial, theeffluent was subjected to electrooxidation in the second stage.

Conventional coagulation

The effectiveness of some commercially available coagulantsprocured from EAU chemical manufacturing company was alsoattempted. The TOC removal at different coagulant dosages wasstudied and the results were tabulated in Table 3. The resultssuggest that maximum TOC removal of 50% could be achieved byusing commercial coagulants. However, the turbidity of wastewa-ter could not be reduced.

Electrooxidation

Electrooxidation is an effective method for degradation oforganic pollutants. Stable electrode materials like Ti/IrO2–Ta2O5

and TiO2 nanotubes grown on titanium sheet (TiO2 NT) were triedas electrodes. TiO2 is n-type semiconductor with a band gap of

Table 3Effect of some commercial coagulants on TOC removal.

S. no. Coagulant Coagulant

dosage (ppm)

TOC (ppm)

after coagulation

% TOC

removal

1 P 2895 5 90.4 53.4

10 97.7 49.7

15 97.0 50.0

2 P 5340 5 94.3 51.4

10 101.6 47.6

15 113.8 41.4

3 P 2910 5 96.7 50.2

10 94.5 51.3

15 94.3 51.4

4 P 5001 5 109.8 43.4

10 112.3 42.1

15 114.0 41.2

5 P 5003 5 102.4 47.2

10 100. 7 48.1

15 100.6 48.2

6 P 5005 5 92.8 52.2

10 92.3 52.4

15 91.9 52.6

7 P 5009 5 98.0 49.5

10 98.1 49.4

15 97.5 49.8

0 2 4 6 8 100

20

40

60

80

TO

C r

em

oval %

Time ( h)

TiO2 NT

Ti/IrO2-Ta

2O

5

Fig. 6. Effect of anode material on TOC removal (current density: 12.6 mA cm�2).

0 2 4 6 8 100

20

40

60

80

b

TO

C r

em

oval %

Time (h)

12.5 mA/cm2

25 mA/cm2

37.5 mA/cm2

0 1 2 3 4 5 6

0

50

100

150

Zero order

R2

Current density

TO

C r

em

oval m

gL

-1

Time (h)

12.5mAcm-2 0.970 0

25.0mAcm-2 0.937 1

37.5mAcm-2 0.933 9

Fig. 7. (a) Effect of current density on TOC removal and (b) kinetics of TOC removal.

N. Lakshmi Kruthika et al. / Journal of Environmental Chemical Engineering 1 (2013) 183–188 187

3.2 eV. Depending on its crystal structure and the nature oftitanium, it varies from 3.2 to 3.5 eV. Furthermore, the material iscorrosion resistant, biocompatible, non-toxic and self-cleaning.

Effect of electrode material

The oxidation of the organics present in the wastewater wasstudied using TiO2 NT and Ti/IrO2–Ta2O5 electrodes separately atan applied current density of 12.5 mA cm�2. The results shown inFig. 6 clearly indicate that the oxidation of the effluent in thepresence of TiO2 NT electrode is better. Around 80% of the organicmatter was eliminated in the presence of TiO2 NT electrode while itis hardly around 58% with Ti/IrO2–Ta2O5 electrode. The concen-tration of chloride ion was measured during electrooxidation andfound to be decreased to 30,450 ppm from its initial concentrationof 34,083 ppm. This indicates the anodic discharge of chlorine asrepresented below

2Cl� ! Cl2þ 2e� (7)

Since the experiments were conducted around neutral pH,entire chlorine is expected to be in the form of HOCl and OCl�

species whose solubility is high in aqueous solution [18]. Theoxidation of pollutants may also occur by oxidation of chlorideinvolving active chlorine (HOCl and OCl�).

Cl2ðaqÞ þ H2O ! HOCl þ Hþ þ Cl� (8)

It is known that the oxidation of organics in the presence of‘‘active’’ and dimensionally stable anodes like IrO2/TaO2/RuO2

coated titanium was attributed to the formation of ‘‘higher oxides’’[19] via adsorption of hydroxyl/oxy chloride radical which can berepresented as

MOxþ OH� ! MOxðOH�Þ ! MOxþ1þ Hþ þ e� (9)

MOxþ OCl� ! MOxðOCl�Þ þ Cl� ! MOxþ1þ Cl2þ e� (10)

In the presence of oxidizable organics, the chemisorbed activeoxygen will participate in the formation of selective oxidationproducts where as physisorbed active oxygen leads to completedegradation to CO2 and H2O [20]. Serikawa et al. [21] haveobserved strong catalytic effect while converting organic pollu-tants to innocuous CO2 and H2O in the presence of chloride ion. Itis also apparent that the indirect electrooxidation involving

various forms of chlorine was a predominant process in removingorganic pollutants. Consequently, the oxidation of effluent is poorunder Ti/IrO2–Ta2O5 electrode. Better oxidation by TiO2 NTelectrode may be attributed to the difference in band gap andspecific surface area. It is evident that the TiO2 nanotues grown onTi-surface are intact and active even after prolonged usage forseveral hours. The SEM–EDAX analysis of the electrode surfaceindicates the presence of minor amounts of Ca2+, Cl� and N. Thepossibility of passive film on the anode surface can be discountedbecause of continuous generation of hypochlorite ions in aqueoussolution.

Effect of current density

The degradation of organics using TiO2 nanotubes as anode andat different current densities was studied and the results arepresented in Fig. 7a. From the results it is apparent that the TOCremoval was found to increase with current density that too only atthe initial stage. Also, it was observed that the TOC removal beyond25 mA cm�2 is very marginal. In general, if the applied current ismore than the limiting current, the oxidation will be invariablyunder mass transport control and the oxygen evolution dominatesthe Cl� oxidation. This may be the reason for the marginal TOCremoval at higher current densities of 25 and 37.5 mA cm�2.

N. Lakshmi Kruthika et al. / Journal of Environmental Chemical Engineering 1 (2013) 183–188188

During the process, the concentration of Cl� was decreased from34,083 mg/L to 30,674 mg/L indicating the discharge of chlorine atthe anode. Maximum removal of 80% is attained even at a lowcurrent density of 12.5 mA cm�2. The kinetic data on TOC removalpresented in Fig. 7b clearly suggests that the degradation oforganics follow zero order rate expression. This implies thatelectrooxidation is current control process where the pollutantmolecules arrive at the anode faster than the electrochemicalproduction of oxidant.

Conclusions

The efficacy of electrochemical techniques viz. electrocoagu-lation and electrooxidation for the treatment of wastewatergenerated from gelatin production industry was studied. Theinitial TOC of 194.4 ppm was reduced to 82 ppm by electro-coagulation using aluminum and steel electrodes. However, theperformance of the electrocoagulation was drastically affecteddue to formation of CaCl2 scales over the electrodes. Afterprecipitation of calcium ion as calcium carbonate, the perfor-mance of the electrodes was significantly improved. Aluminumelectrodes of different geometry viz. cylindrical rod andhexagonal rod were used as anode. The role of electrodegeometry on scaling was observed to be very marginal. Theenergy consumption for electrocoagulation was estimated to be0.09 Wh/L. Coagulation by commercial coagulants was also triedand found to be less effective compared to electrocoagulation.After processing the wastewater by electrocoagulation, theprocessed wastewater was subjected to electrooxidation forfurther purification. Among the electrodes tried as anode, TiO2

NT (TiO2 nanotubes grown on titanium) was found to be bettercompared to Ti/IrO2–Ta2O5. The decrease in TOC is 58% in thepresence of IrO2–Ta2O5 coated Ti electrode whereas about 80%was achieved using TiO2 NT electrode. Thus the overall TOCcould be brought down to 12–15 ppm from the initial value of195 ppm. The study indicates that the combination of electro-coagulation and electrooxidation techniques is amenable for thetreatment of wastewater generated from gelatin productionplant.

Acknowledgement

The authors are thankful to Director, CSIR-NML for permissionto publish this work.

References

[1] J.P. Maree, C.G.B. Cole, A. Gerber, J.L. Barnard, Treatment of gelatin factory effluent,Water SA 16 (1990) 265–268.

[2] S.D. Gatnekar, D.S. Ghalsasi, B.M. Tamhane, The novel three tier biotechnology toconvert solid waste of gelatin manufacturing unit into useful plant probiotics,Indian J. Environ. Protect. 29 (2009) 767–774.

[3] S.D. Gatnekar, M.F. Kavian, S.M. Sharma, S.S. Gatnekar, G.S. Gatnekar, A.V. Gatne-kar, Application of vermin filter based effluent treatment plant (pilot plant) forbio-management of liquid effluents from the gelatin industry, Dyn. Soil Dyn. Plant4 (2010) 83–88.

[4] S.D. Badrinath, S.N. Kaul, V.P. Deshpande, S.K. Gadkari, Ossein wastewater char-acterization and treatability study, Water Res. 25 (1991) 1439–1445.

[5] M. Muthukumar, M. Thalamadai Karuppiah, G. Bhaskar Raju, Electrochemicalremoval of CI Acid orange10 from aqueous solutions, Sep. Purif. Technol. 55(2007) 198–205.

[6] G. Bhaskar Raju, M. Thalamadai Karuppiah, S.S. Latha, S. Parvathy, S. Prabhakar,Treatment of wastewater from synthetic textile industry by electrocoagulation–electrooxidation, Chem. Eng. J. 144 (2008) 51–58.

[7] M. Murugananthan, G. Bhaskar Raju, S. Prabhakar, Removal of tannins andpolyhydroxy phenols by electrochemical techniques, J. Chem. Technol. Biotech-nol. 80 (2005) 1188–1197.

[8] P. Lakshmipathiraj, G. Bhaskar Raju, M. Raviatul Basariya, S. Parvathy, S. Prabha-kar, Removal of Cr (VI) by electrochemical reduction, Sep. Purif. Technol. 60(2008) 96–102.

[9] C. Comninellis, A. Nerini, Anodic oxidation of phenol in the presence of NaCl forwastewater treatment, J. Appl. Electrochem. 25 (1995) 23–28.

[10] J. Iniesta, E. Exposito, J. Gonzalez-Garcia, V. Montiel, A. Aldaz, Electrochemicaltreatment of industrial wastewater containing phenols, J. Electrochem. Soc. 149(5) (2002) D57–D62.

[11] D. Rajkumar, K. Palanivelu, Electrochemical treatment of industrial wastewater, J.Hazard. Mater. 113 (2004) 123–129.

[12] H.D. Doan, J. Wu, R. Mitzakov, Combined electrochemical and biological treat-ment of industrial wastewater using porous electrodes, J. Chem. Technol. Bio-technol. 81 (2006) 1398–1408.

[13] G. Chen, Electrochemical technologies in wastewater treatment, Sep. Purif. Tech-nol. 38 (2004) 11–41.

[14] B.O. Regan, M. Gratzel, A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films, Nature 353 (1991) 737–739.

[15] C.S.E. Lenore, A. Greenberg, A.D. Eaton, Standard Methods for the Examination ofWater and Wastewater, 18th ed., American Public Health Association, Washing-ton, DC, 1992.

[16] Z. Gu, Z. Liao, M. Schulz, J.R. Davis, J.C. Baygents, J. Farrel, Estimating dosing ratesand energy consumption for electrocoagulation using iron and aluminum elec-trodes, Ind. Eng. Chem. Res. 48 (2009) 3112–3117.

[17] G.E. Thompson, G.C. Wood, Anodic films on aluminum, treatise on materialscience and technology, in: J.C. Scully (Ed.), Corrosion: Aqueous Processes andPassive Films, vol. 23, Academic Press, New York, 1983.

[18] N.A. Lange, Hand Book of Chemistry, 10th ed., McGraw Hill Book Company,London, 1967.

[19] M. Panizza, G. Cerisola, Electrochemical oxidation as a final treatment of synthetictannery wastewater, Environ. Sci. Technol. 38 (2004) 5470–5475.

[20] S. Raghu, C. Ahmed Basha, Chemical or electrochemical techniques, followed byion exchange, for recycle of textile dye wastewater, J. Hazard. Mater. 149 (2007)324–330.

[21] R.M. Serikawa, M.Q. Isaka, Su.T. Usui, T. Nishimura, H. Sato, S. Hamada, Wetelectrolytic oxidation of organic pollutants in wastewater treatment, J. Appl.Electrochem. 30 (2000) 875–883.