Electrochemical cell of requiredvolume was fabricated. Iron/Copper plates were used as electrodes (anodes andcathodes) and arranged in bipolar configuration. EC reactor is filled with 1.5Lof raw sample, placed on magnetic stirrer. Electrodes were connected to thepositive and negative terminals of the DC power supply. Experiments werecarried out at different Voltages and at pre-optimized 9V, 430 Rpm fordifferent time intervals, different electrode material.
Electrode spacing wasmaintained 1cm using separating stand. The sample were retrieved from thereactor was filtered using A1 filter paper and filtrate used for thecharacterization. 1.2.
BatchECC studiesExperiments were carried with 4 electrodesarranged in bipolar condition. Only the outer electrodes were connected to theDC power source to form bipolar system. Magnetic stirrer helped to maintain ahomogeneous solution in the batch reactor. Electrode plates were washedmanually using scrubber and then washed with 15% acid solution followed bydistilled water prior to use. The treated samples retrieved after each run werefiltered and the filtrate was used to analyze the change in different waterquality parameters. 1.3.
Settling and FilterabilityThe mixture of sludge and supernatantfrom EC process were mixed well, and resultant slurry used for settling andfilterability studies. Settling studies carried using graduated cylinder. Thewell mixed slurry was homogenized before pouring in to cylinder and was allowedto settle. The position of interface was measure as function of time. Eachsettling experiment done up to 45 min time interval. The filterability of the sludge was tested using gravimetricfilter paper supported over funnel and graduated cylinder column.
Dry Filterpaper weighed. A known volume of homogenized slurry was taken in a beaker andpoured in to the funnel. The volume of filtrate collected in the graduatedvertical cylinder with regular interval of time. Each filterability experimentdone up to 70-75min time interval. The cake formed in the funnel is removedcarefully and weighed. 1.4.
Membrane FiltrationMembrane filtration done using membrane holding unit of size –(L×W×D) – 12×5×17cms, made up of Perspex material, Peristaltic pump andMembrane made up of Tubular PVDF membrane having Pore size 0.1µm, Membranearea: 0.5sq.m and Size: W×H = 13×16cms. Supernatant from batch ECC ispassed through membrane in submerged condition. Filtration process carried forflow rate of 2.5L/hr. The filtrate was used to analyze the change in differentwater quality parameters like COD, TS and TDS.
2. Resultsand discussions3.1. Batch ECC studies for different operating parameters using Fe electrodesBatch ECCexperiments carried out to study COD degradation for different operatingconditions like various voltages with 2E, 90min ET and with 4E, 60min ET, 9Vand 2 different initial temperature of raw wastewater.
3.1.1.COD degradation as a function of electrolysis time at different applied voltageusing 2EBatch ECC experiments carried outusing 2 Fe electrodes for different operating conditions with 1V, 2V, 3V, 6V& 8V, 90min ET. Fig2 COD degradation as a function of electrolysis time at different appliedvoltage using 2Electrodes The Fig 2 shows COD removal for 1V,90min ET is 35.54% r, for 2V 90min ET is 71.
6%, For 4V 90min ET is 76%, for 6V90min ET is 80% and for 8V 90min ET 83%. For 8V, COD degradation almostconstant at 70, 80 and 90min ET. 3.1.
2.Effect of Initial Temperature on COD removalBatch ECC experiment carried out forthe sample taken out from preservation having the initial temperature of 6oCand for sample having room temperature 26oC using Iron electrodesfor different operating parameters with 4E, 9Volt, 430Rpm and 60minElectrolysis time. The samples were taken out at time intervals of 5, 10, 15,20, 30, 45 and 60mins in each set and the samples were filtered using A1 filterpaper. Filtered samples were used for analysis of COD. The Fig 3 shows the CODdegradation curves as a function of electrolysis time at starting temperatureof 6oC and 26oC. Fig3 COD degradation curves as a function of electrolysis time at startingtemperature of 6oC and 26oC (COD 1280-1310mg/l, pH06.66) Initial COD for initial wastewatertemperature of 6oC was 1280mg/L and initial COD for initialwastewater temperature of 26oC was 1310mg/L. The plot show lower thewastewater temperature favored less COD removal.
At 20min ET maximum CODremoval was observed at ambient operating temperature 26oC; the rest40min of total ET of 60min was allowed for floc formation and aggregation. 3.2.Batch ECC studies on sludge floc formation at different ET, minSeparate batch ECC experiment carriedout for ET 5, 10, 15, 20, 30, 45 and 60min using Iron electrodes with 4E,9Volt, 430Rpm. ECC treated slurry was kept under observation to see the sludgeformation.
Treated slurry sample taken for analysis of TS of slurry and thesample of treated supernatant was taken for analysis of TS of Supernatant.Electrodes weighed before and after treatments. Initial and final pH ofsolution in EC reactor was noted for each set of experiments. Fig 4 shows the Effect of Electrolysis Timeon Sludge floc formation. Fig 4 Effect of Electrolysis Time onSludge floc formation The plotshows no sludge floc formation in 5, 10, 15, 20min of ET. After EC treatmentfor each ET, when treated sample was kept under observation, no sludgeformation and no settling was observed. In 30min ET there was slight sludgefloc formed with a final dried weight of sludge of 0.
5421g. In 45 min ET and 60min ET Sludge formationwas higher with a final dried sludge weighing 1.7921g and 1.9201g respectively. 3.3.
Batch ECC studies on Electrode dissolution as a function of change in bulksolution pHFig 4.4shows the Electrode dissolution as a function of change in bulk solution pH. Electrode dissolution and pH changeof bulk solution during batch ECC showed step change in values during ECC.Electrode dissolution curve shows two plateaus namely, plateau 1 from 5 to 30min ET; and plateau 2 from 45 to 60 min ET. Bulk solution pH shift from 7.73 to8.84 was observed between 15 to 20min ET during ECC 10 min prior to maximumelectrode dissolution between 30 and 45min respectively. Electrode dissolutioncauses increase in the solids concentration in the bulk solution during ECC.
3.4.Batch ECC studies on TS removal at different ETFig 5 showsEffect of Electrolysis time on TS removal.As can be seen from the curves, total solids (TS) were seen to increase in thebulk solution during ECT from its initial value of 1425mg/L to 2457mg/L at theend of ET of 60 min. Sludge formationbegins at ~ 45min ET to reach stable levels at 60min. TS value in thesupernatant after 60min ECC was 706mg/L showing a total solids removal of ~51%. Fig 4.4 Electrode dissolution and bulksolution pH as a function of ET Fig 5 Effect of TS removal onElectrolysis time3.
5. Batch ECC studies for differentoperating parameters using Cu electrode Batch ECCexperiments carried out using Cu electrodes for various operating parameters tosee the effect of initial temperature on COD removal, Sludge formation fordifferent ET. 3.6.Effect of Initial Temperature on COD removalBatch ECC experiment carried out forthe sample taken out from preservation having the initial temperature of 6oCand for sample having room temperature 26oC using Iron electrodesfor different operating parameters with 4E, 9Volt, 430Rpm and 60minElectrolysis time. The samples were taken out at time intervals of 5, 10, 15,20, 30, 45 and 60mins in each set and the samples were filtered using A1 filterpaper.
Filtered samples were used for analysis of COD Table 2 Residual COD in ECC treatedeffluent for different initial temperature Sl No ET, min COD mgL-1 @60c COD mgL-1 @260c 1 0 1664 2240 2 5 928 896 3 10 896 768 4 15 864 768 5 20 768 704 6 30 704 640 7 45 640 582 8 60 608 512 Table 2 shows the residual COD in theECC treated effluent for different initial temperature of wastewater. It showsthe COD removal of 63% for 60c and 77% 260c at 60min ET.Therefore 260c is an ambient initial temperature compared topreservation temperature of 60c.
Using Cu electrode removalefficiency of COD is less and not reached discharge limit standard of 250 mgL-1. 3.7.Batch ECC studies on sludge floc formation at different ET minSeparate batch ECC experiment carriedout for ET 5, 10, 15, 20, 30, 45 and 60min using Iron electrodes with 4E,9Volt, 430Rpm. ECC treated slurry was kept under observation to see the sludgeformation. It is observed that no sludge formation in 5, 10, 15, 20, 30 and45min ET. For 60 min ET the sludge flocformed with a final dried weight of sludge of 1.1477g.
No clearseparation of solid /liquid interface is observed using Cu electrodes. 3.8. Batch ECC studies for differentelectrodes on Settling, Filterability, Electrode dissolution and CODdegradationSeparate ECCstudies carried out for 3 different electrodes 4Fe, 4Al, 4Cu for 60min ET, and9V.
Settling and filterability studies carried on each set of experiments. Sampleswere retrieved for the analysis of COD and Electrodes were weighed before andafter experiments. 3.9.
Settling characteristics fordifferent electrodesSettlingexperiment carried out for ECC treated slurry using different electrodes. Fig 6shows the settling characteristics for different electrodes Fig 6 Settling characteristics fordifferent electrodes The Fig 6shows the volume of sludge settled interface (vs) time in minutes. As can beseen from the curves Fe electrode showed better settling compared with Al andCu. Settling after Fe electrode conducted EC is quite faster, likely due todifferent morphology of iron hydroxide particles, which are better defined andhigher density than Al hydroxide. Dotted line indicates band settling/ nosettling depending on the electrode material up to 15min for Cu and 5min forFe.
Discrete and compression settling is seen to dominate all the four settlingregimes. 3.10. Filterability Characteristics ofsludge for different electrodesFilterabilityexperiments carried out for BECC treated slurry using different electrodes. Fig7 shows Filterability Characteristics of sludge for different electrodes assacrificial anodes. Fig 7 Filterability Characteristics ofsludge for different electrodes Fig 7 showsthe plot of as afunction of volume, V. As can be seen from plot Fe electrode show betterfilterability compared to Al and Cu. Cu electrode showed better compared to Alelectrode.
Low filterability is ascribed to poor sludge formation or filterblockage during filtration. Poor filtration using Cu electrode is may be due tono separation of solid/liquid interface and for Al electrode may be due to thegel floc formation which will be dispersed in slurry or gel particles getentrapped into the filter medium which inhibit filtration. Pressure filtrationcould possibly improve filtration in particular with Fe electrode. 3.11. Electrode dissolution fordifferent ElectrodesSeparate ECCstudies carried out for 3 different electrodes 4Fe, 4Al, 4Cu for 60min ET, and9V.
Electrodes weighedbefore and after treatments to observe the electrode consumption/ electrodedissolution during treatment. Fig8 shows Electrode dissolution for different Electrodes. Fig 8 Electrode dissolution fordifferent Electrodes. As can beseen from plot, anode electrode dissolution is more and cathode is less for Fe,Anode dissolution and cathode dissolution almost same for Al, and highest anodedissolution and very less cathode dissolution for Cu compared to Fe & Al. 3.
12. COD degradation for differentelectrodesSeparate ECCstudies carried out for 3 different electrodes 4Fe, 4Al, 4Cu for 60min ET, and9V. The samples weretaken out at time intervals of 15, 30, 45, and 60mins and the samples werefiltered using A1 filter paper. Filtered samples were used for analysis of COD.Fig 9 shows COD degradation fordifferent electrodes Fig 9 COD degradation for differentelectrodes Fig 9 showsthe plot of COD (vs) ET. As can be seen in plot Al electrode is better for CODdegradation compared to Fe & Cu. COD removal of 96% for Al, 95% for Fe& for Cu 88.
6%. Use of Fe electroderesults in the formation of very fine brown particles and for Al electrode gelfloc formed which may cause less degradation of COD in Fe compared to Al. UsingCu electrode very less COD degradation is may be due to partial treatment.
3.13.Change in water quality for ECC treated effluent followed by membranefiltrationAfter batch ECC experiments using Feelectrodes at 9V, 60min run the EC treated supernatant was further passedthrough a membrane filtration unit having membrane of pore size 0.1µm to refinethe ECC treated effluent for possible enhancement of water quality. Removal ofTS, TSS, TDS and COD were studied for membrane treated effluent to attain thedesired water quality parameters. Table 3 shows the characterization of ECC effluent and membrane filtration. Table 3 Characterization of ECCeffluent and membrane filtration Sl No Parameters Unit Raw wastewater ECC Effluent Membrane Filtration Effluent Values Values % removal Values % removal 1 COD mgL-1 4800 224 95.3% 42 99% 2 TS mgL-1 2600 1140 56% 90 96.
5% 3 TSS mgL-1 314 260 17.2% 0 100% 4 TDS mgL-1 2286 446 80.4% 90 96% Initial CODof textile wastewater was 4800 mgL-1 which came to verylow level of 42 mgL-1 after membrane filtration.
ECC showed 95.3%COD removal, 56% TS removal, 17.2% TSS removal and 80.4% removal of TDS.
Membrane filtration showed 99% removal of COD, 100% TSS removal, 96.5% ofremoval of TS and 96% of TDS removal. ECC will remove colour and COD, TS ofabout 80% effectively but iron electrode will give light brown colour to thetreated water.
To refine these deficiencies membrane filtration can be used. 3.14.Point of zero charge (pHpzc)Point of zero charge (pHpzc) for ECgenerated sludge treating textile wastewater for both iron and aluminum wasdone using ‘solid addition method’. Fig 4.10 shows point of zero charge. Fig 4.
10 Point of Zero Charge The plot shows point of zero charge (pHpzc)for EC generated sludge treating textile wastewater for both iron and aluminumwas done using ‘solid addition method’. The zero value of ?pH lies at the pH0value of 8.70 for iron electrodes and 9.41 for aluminum electrodes, which isconsidered as the pHpzc of the dried sludge obtained from the batchtreatment of raw textile wastewater.
3. ConclusionsIron electrodes with 4 electrodeconfiguration provided maximum COD removal ranging from 70-88% at initialwastewater temperatures of 6oC and 26oC from its initialCOD value of ~1270mg/L. Copper electrodes with 4electrode configuration showed less COD removal efficiency compared to Ironelectrode due to no solid liquid separation during treatment even thoughmaximum electrode dissolution. Al electrode is better for COD degradation compared to Fe and Cu. CODremoval of 96% for Al, 95% for Fe & for Cu 88.6%. Dry sludge was of the order of 0.36, 1.
19, and 1.28kg/m3 of rawtextile wastewater treated which is less compared to other treatment methods. Fe electrode showed better settling compared with Al and Cu. This maylikely due to, different morphology of iron hydroxide particles, which arebetter defined and higher density than Al hydroxide. And also use of iron electrode often results in the formation of veryfine brown particles which are more prone to settling than gel floc formed withAl. Fe electrode showed better filterability compared to Al and Cu. The zero value of ?pH lies at the pH0value of 8.
70 for iron electrodes and 9.41 for aluminum electrodes, which isconsidered as the pHpzc of the dried sludge obtained from the batchtreatment of silk textile wastewater. TSvalue in the supernatant after 60min ECC showing a total solids removal of~56%.
Membrane filtration showed 99% removal of COD, 100% removal of TSS, 96.5%of removal of TS and 96% of TDS removal and can be used for reclamationpurposes. Hence the overall studies confirmed that combined treatment ofElectrochemical coagulation and membrane filtration is efficient in degradationof organics from silk textile wastewater. AcknowledgementThe author wish to thank JSSMahavidyapeetha, Mysuru, Karnataka, Sri Jayachamarajendra College ofEngineering, Mysuru, JSSTI campus, Mysuru, Karnataka and JSS Academy ofTechnical Education, Bengaluru, Karnataka for extending laboratory facilitiesto carry out this research work.