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*Corresponding author.Tel:+90-312-2977404;fax:+90-312-2992124.E-mail address:tanyolac@.tr (A.Tanyola -c ).0043-1354/03/$-see front matter r 2002Elsevier Science Ltd.All rights reserved.PII:S 0043-1354(02)00523-7reactant,andthe removal of prod ucts from the reaction zone,meanwhile decreasing the available potential to drive the reaction[15].There are different configurations of electrochemical reactors employedfor the electrochemical oxid ation of phenol.Smith de Sucre and Watkinson[3]usedlead dioxide packed-bed anodes for phenol oxidation.The authors reportedthat all the phenol in solution couldbe readily oxidized but complete organic carbon removal was more difficult.Chettiar and Watkinson[11]usedan electrochemical system adapted from the previous work of Smith de Sucre and Watkinson[3]using a coated graphite plate with an electrodeposited PbO2anode. According to their results the phenolics were largely destroyed,however,organic degradation products such as quinone andhyd roquinone remainedin the solution. Sharifian andKirk[21]useda packed-bedreactor of PbO2pellets with recirculating anolyte in order to follow the phenol loss andbenzoquinone,maleic acidandCO2 formation.The authors statedthat benzoquinone,an intermediate product,formation was favoured by high current andpH andby low phenol concentration, temperature,andd issolvedoxygen at relatively short electrolysis times.Gattrell andKirk[2]usedaflow-by electrochemical cell with a peristaltic pump to feedthe phenol solution through the anode in an upward direction.The authors reported that increasing cell voltage increased the amount of oxidized products along with increasing electrode corrosion and decreasing current efficiency.It was also concluded that higher phenol concentrations(over1880mg lÀ1)showeda shift in product distribution to favour less oxidized,mostly insoluble products while elevated temperatures(about 501C andhigher)showeda markedability to red uce electrode passivation and increase the phenol oxidation rate.K.otz et al.[18]andStucki et al.[22]useda bench-scale general-purpose reactor from ElectroCell AB equippedwith up tofive SnO2anodes.The authors concluded that the oxidation efficiency was independent of the pH of the water and the oxidation of a wide range of organic compounds proceeded with an efficiency about5times higher than platinum anodes without any corrosion on cathode.In their work,oxidation efficiency for the process was between30and40%with a power consumption of40–50kWh kgÀ1COD -ninellis andPulgarin[12]useda two-compartment cell with an anode made of SnO2coatedtitanium anda cathode made of a platinum spiral enclosed in a porous porcelain pot.Stirring was provided with a magnetic bar in the reactor,there were only small amounts of aromatic intermediates formed at the anode,and aliphatic acids were rapidly ninellis and Nerini[13]usedan electrochemical system ad aptedfrom the previous work of Comninellis andPulgarin[12] using Ti/SnO2andTi/IrO2anodes in the presence of NaCl to oxidize the phenol anodically.They noted that the presence of NaCl catalysedthe oxid ation reaction of phenol at Ti/IrO2anode,however did not affect Ti/SnO2 anode proving that electrochemical oxidation reaction was depending on both electrolyte type and anodic material.Boudenne et al.[9]usedaflow-by electro-chemical cell with a stack of21Pt/Ti grids consisting of a cooling tub anda pump.The authors conclud edthat electrochemical degradation of phenol with carbon black is much quicker than biological degradation and other electrochemical treatments using different cataly-sis such as TiO2for photo oxidation.Lin et al.[20]used a batch system with four pieces of cast iron cathode and anode for phenol removal from saline wastewater.The authors reportedthat with a proper current input,the COD removal of the electrochemical treatment couldbe considered improved in comparison to that in biological treatment.The application of the tubular electrochemical reactor has been made only recently in literature.Israilides et al.[17]andVlyssid es et al.[25]useda recirculation reactor with a tubular electrolytic cell consisting of stainless steel cathode and titanium alloy anode placed at the centre of the reactor to treat olive oil wastewater andvinasse from beet molasses treatment,respectively.The authors operate the batch,laboratory-scale pilot plant system at15V DC and100A.Israilid es et al.[17]reportedthat after10h of electrolysis at0.26A cmÀ2current density, total COD,TOC,VSS were reduced by93%,80.4%and 98.7%,respectively,with the energy consumption of 12.3kWh kgÀ1COD removed,being an unfeasible process.In another work of the tubular reactor,Vlys-sides et al.[40]useda similar reactor to that of Israilid es et al.[17]for the oxidation of textile dye wastewater.The authors operatedthe lab-scale pilot plant recirculated reactor continuously at20V DC and50A.They concluded that the system could be used for effective textile dye wastewater oxidation or a feasible detoxifica-tion andcolour removal with a mean energy consump-tion of21kWh kgÀ1COD removed.During the electrochemical conversion of phenol,an electrolyte is added to the medium to increase con-ductivity and in return current density.Various electro-lytes such as Na2SO4,H2SO4andtheir mixtures were usedin literature[2,3,11,12,18,21]but very few investi-gators[13]made use of NaCl mainly due to toxic intermediates produced such as mono,di and tri-substitutedchlorophenols when utilized[29,30].When electrolysis of aqueous NaCl solution is attempted,Cl2 gas is discharged on the anode above2.1872V potential [31,32].Following the discharge of Cl2gas [14,20,25,31,32]HOCl formation occurs with hydrolysis reaction[14,20,33],which is consumedby the ionization reaction with the formation of OClÀ[14,33].Meanwhile, HOCl is replenishedin the med ium with the electro-chemical reaction of NaCl.Hypochlorous acid,HOCl,is a strong oxidant,which oxidizes the phenol in solutionB.K.K.orbahti,A.Tanyola-c/Water Research37(2003)1505–1514 1506while OClÀis also consumed[13,17,25].This represents the indirect oxidation of phenol,however direct oxida-tion occurs on the electrode[20],most likely with a different mechanism.On the cathode H2O molecules are reduced and H2gas along with hydroxyl ions are produced.In this study,application of the continuous tubular reactor for phenol removal through electrochemical oxidation was realized for thefirst time in literature.In the work,the effect of residence time on electrochemical treatment of synthetic phenolic wastewater was investi-gatedat low andhigh phenol feedconcentrations.Other operational parameters were directly used in the runs with their optimum values determined previously[34]. Column outlet pH andphenol concentration andthe energy consumedwere monitoredcontinuously,and periodic GC/MS analysis of the reaction mixture in a specifiedbatch run was carriedout to d etermine the fate of toxic intermediate products.2.Materials and methods2.1.Chemicals and materialsPhenol andNaCl were obtainedfrom Merck(99.5% pure)and double distilled water was used for the preparation of synthetic wastewater.All solvents used for the analysis were also obtainedin extra pure condition from Merck.Carbon electrode(Meteor, Germany)usedin the runs(cylind rical,D¼1:32cm) was originally designed and manufactured for DC electric motors to endure high voltage and current loads.Stainless steel6R35(Sandvik,Sweden)was used as cathode material(cylindrical,OD=8.89cm and wall thickness=2mm)with a weight percentage chemical composition of0.045C,0.40Si,1.18Mn,0.026P,0.001 S,17.45Cr,10.14Ni,0.46Ti,andthe rest F e.2.2.Experimental set-upA continuous electrochemical tubular reactor was designed in our laboratory with a net working volume of 1934cm3[35](Fig.1).The35cm tall reactor (OD=8.89cm)was constructedfrom stainless steel (Sandvik,Sweden)with a heating/cooling coil around. The carbon electrode was used as the anode material andplacedat the centre of the reactor.A Cole Parmer model peristaltic Masterflex s pump was usedto pump the phenol feedin electrolyte solution from a20-l reservoir.The reaction temperature was controlledwith circulating water recycledfrom a temperature-controlled water bath(New Brunswick,G-86)andmonitoredwith glass thermometers immersedin the exit andinlet of the column.The current was appliedby a constant voltage/ current-controlledDC power source(NETES NPS-1810D).Fig.1.The schematic view of continuous electrochemical tubular reactor((1)carbon electrode,(2)plexiglas screws,(3)plexiglas reactor cover,(4)d ischarge line,(5)heating/cooling coil,(6)reactor support,(7)reservoir,(8)feedpump,(9)feedline,(10) connections,(11)DC power source).B.K.K.orbahti,A.Tanyola-c/Water Research37(2003)1505–151415072.3.Experimental procedureSynthetic phenolic wastewater with the electrolyte was preparedin the wastewater reservoir at specified concentration andwas fedto the column tofill it completely.An initial sample of10ml was taken from the reservoir to determine the initial phenol concentra-tion prior to reaction.The reaction startedwith the application of the specifiedvoltage andcurrent and,the recycling water for temperature control was pumped through the reactor coil while feedstream was pumped to the column continuously.At appropriate time intervals,samples of10ml were taken from the reactor outlet and analysed to determine the intermediate properties of the reaction medium during electrochemi-cal conversion.DC power source was turnedoff andthe reaction was terminated after steady state reached.2.4.Reaction conditionsThe phenolic wastewater was usedwith450and 3100mg lÀ1initial phenol concentrations in the runs at 251C reaction temperature with120g lÀ1electrolyte concentration.F or450and3100mg lÀ1initial phenol concentrations,the appliedcurrent d ensity was61.4and 54.7mA cmÀ2,respectively.The values of temperature, electrolyte concentration andcurrent d ensity applied were determined to be optimum through batch runs for maximum phenol removal rate in a previous work[34].2.5.AnalysisThe change in phenol concentration of the reaction medium was determined by means of a Cecil1100 HPLC system.The system was equippedwith a variable wavelength monitor(CE11220)operating at254nm anda Cecil HPLC pump system(CE1100).Chromato-grams were obtainedusing a Hichrom-S5OS1column (Chromosorb).Only one mobile phase,running at ambient temperature,was elutedand20m l sample was injected.Methanol/water(40/60,v/v)was used as the mobile phase andtheflow rate was ad justedto 1ml minÀ1under28MPa pressure.Before the analysis, the mobile phase wasfilteredandsonicatedin ord er to remove dissolved gases.GC/MS analyses were performedwith a5972MSD connectedto a5890HP s GC system in order to determine the intermediate products formed during the electrochemical reaction in a specifiedbatch run.F or the analysis,5ml liquidsample was taken from the reactor at appropriate time intervals.The pH of the sample was adjusted to3with HNO3andaqueous phase was saturatedwith NaCl.Then the sample was extractedfor 20min with5ml of diethyl ether,organic phase was separatedin a separation funnel,and1m l of ether phase was injectedinto GC/MS system.A DB-1capillary column was usedfor the separation andoven tempera-ture was programmedas constant501C for1min,andthen increasedto2501C with201C minÀ1rate andfinally10min at2501C.Automatic injection system was kept at250–2801C while mass detector temperature was held at2801C.For identification of the products,standardsamples andWiley library search were used.Then,internal calibration was appliedusing a stand ard(dichlorophenol)with response factor0.99to calculatecorresponding concentrations of compounds based onthe area under the curve.For polymer,4–5peaks weredetected with their respective mass number values andindividual weight concentrations were calculated.Theresults were presentedas percent of the initial phenolpresent in the wastewater.3.Results and discussionsContinuous tubular reactor experiments were carriedout for the determination of the effects of the residencetime on phenol conversion at optimizedcond itionsdetermined previously through batch runs[34].Phenolfeedconcentration was selectedat low andhigh(450and3100mg lÀ1)concentrations with61.4and54.7mA cmÀ2applied current density for each residence time tovisualize the change in phenol removal performance.Although both feedstreams containedthe same amountof electrolyte,the conductivity of the feed with lowerphenol concentration was observedhigher than that ofhigher phenol feedconcentration.This is basically d ueto the cloud-like polymer formation around the anode athigher phenol concentrations in an unmixedflow systemwith low linear velocity(3o N Re o53),which diminished the current applied.The runs were carried out in doublesandaverage results were presentedinfigures.The d atapoints for duplicate runs at any time were not differentfrom each other more than4%.The passivatingpolymeric formation on electrodes has not been detectedin any run,which,in fact,was observedin literaturestudies.3.1.The effect of residence timeFor450mg lÀ1initial phenol feedconcentration,phenol concentration at the reactor outlet decreasedwith increasing residence time as shown in Fig.2.At10and20min of resid ence time phenol removal was56%and78%,respectively.Above40min resid ence time,allphenol was eventually consumedin the column and100%phenol removal was achieved.During the reac-tions,the colour of the solution at the outlet streamturnedto light yellow from transparent then to d arkbrown due to increased residence time.At higherresidence times,the formation of the suspendedsolidparticles in reaction med ium causedan opaqueB.K.K.orbahti,A.Tanyola-c/Water Research37(2003)1505–1514 1508appearance andthe colour of the solution at the reactor outlet was dark brown due to the formation of polymeric products.Easily separable solid polymeric materials were obtainedat the outlet stream but the formation of polymers did not affect the performance of the column,mainly cell current density.Fig.3shows the pH change at the exit of the column for 450mg l À1phenol concentration,where pH was not controlled.As a general trend,at the beginning reactor outlet pH rised up to pH 11,then began to drop gradually in proportion with the residence time in the tubular reactor,i.e.more residence time caused more pH drop after peak pH.Initial pH rise couldbe attributedto the prod uction of hydroxyl ions on the cathode in the presence of NaCl and pH drop was caused by gradual consumption of hydroxyl anions as well as production of hydrogen cations in dissociation reactions of HOCl and OCl Àalong with the formation reaction of HOCl in the treated waste stream.Short residence time ended up with higher final pH andincrease in resid ence time caused loweredfinal pH values.Nevertheless,resid ence time greater than 20min also causedinstable pH values d ue to unestablished steady-state conditions in the reactor within the time range of runs as well as non-homo-geneous character of the reactor.Stable outlet phenol concentrations were establishedapproximately after 80,70,40,40and30min of elapsedtime for the resid ence time of 10,20,40,60and90min,respectively,andthe corresponding energy requirement per hour at steady state was 1.144, 2.077, 2.679, 3.057and 1.410kWh mol À1consumedphenol,respectively,as shown in Table 1.At steady state,experimental number of electrons consumedper hour was calculatedas 0.33,0.34,0.35,0.26,and0.33mol for 10,20,40,60and 90min of residence time,respectively,in Table 1.Although electron consumption rate values were almost the same,phenol consumption rate decreased in accordwith increased residence time at steady state.Also,specific energy requirement increasedproportionally with residence time except for 90min.At 3100mg l À1phenol feedconcentration,the con-tinuous column reactor reachedstead y state after 5h as shown in Fig.4.At 1,1.5,2and3h of resid ence time,phenol removal was achieved42%,71%,81%and98%,respectively.The increase in residence time increased the phenol removal percentage;however,polymeric pro-ducts formed started to block the reactor discharge at higher residence times due to low volumetric flow rate.Due to high phenol concentration,excessive amount of foam was produced and the colour of the solution was turnedto light yellow from transparent andthen to d ark brown at the outlet stream.The variation of pH in the exit stream of the column for 3100mg l À1phenol feed concentration was depicted in Fig.5.Similar trends of024*********20406080100120p HElapsed Time (min)Fig.3.The change of pH profiles by time at the reactor outlet in the range 10–90min of residence time for 450mg l À1phenol feedconcentration (current d ensity:61.4mA cm À2;T :251C;electrolyte concentration:120g l À1).0501001502002503003504004505000102030405060708090100110120Elapsed Time (min)P h e n o l O u t l e t C o n c e n t r a t i o n (m g l -1)Fig.2.The change of outlet phenol concentration profiles by time in the range 10–90min of residence time for 450mg l À1phenol feed concentration (current density:61.4mA cm À2;T:251C;electrolyte concentration:120g l À1).B.K.K .orbahti,A.Tanyola -c /Water Research 37(2003)1505–15141509Fig.3were also observedin this figure.Except for the residence time of 1h,pH profiles first reached as high as pH 11.5andthen d roppedwith an unstable manner asexplainedfor 450mg l À1phenol feedconcentration.Thesteady-state energy requirement per hour was calculated as 4.345,4.670,5.704and6.379kWh mol À1consumed phenol for 1,1.5,2and3of resid ence time,respectively,as shown in Table 2.At steady state,experimental number of electrons consumedper hour was calculated as 0.24,0.29,0.26and0.28mol for 1,1.5,2and3h of residence time,respectively,in Table 2.In Table 2,electron consumption rate was again almost the same like in Table 1andphenol consumption rate d ecreased proportionally to residence time after 1.5h of residence time.Although there has not been any work done yet with electrochemical treatment of phenol in literature using tubular reactor to compare with our results,there are other works carriedout in d ifferent systems for electrochemical oxidation of phenol.Smith de Sucre andWatkinson [3]achievedcomplete phenol removal within 90and120min reaction time for 525and 1100mg l À1initial phenol concentrations,respectively,at 10A current and8.5V cell voltage in aqueous solutions of Na 2SO 4andH 2SO 4or NaOH using a leadTable 1The energy requirement andelectron consumption rate for 450mg l À1phenol feedconcentration (current density :61.4mA cm À2;T :251C;electrolyte concentration :120g l À1)Residence time (min)Timerequiredto reachsteady state (min)Phenolconsumption rateat steady state (mmol h À1)Specific energyrequirement at steady state(kWh mol À1phenol consumed)Electron consumption rateat steady state (mol e Àh À1)Phenol removal (%)atsteady state108031.1071 1.1440.3356207021.6639 2.0770.3478404013.8871 2.6790.3510060409.2581 3.0570.2610090306.17201.4100.3310002468p HElapsed Time (h)Fig.5.The change of pH profiles by time at the reactor outlet in the range 1–3h of residence time for 3100mg l À1phenol feed concentration (current density:54.7mA cm À2;T :251C;electro-lyte concentration:120g l À1).050010001500200025003000026Elapsed Time (h)P h e n o l O u t l e t C o n c e n t r a t i o n (mg l -1)134578Fig.4.The change of outlet phenol concentration profiles by time in the range 1–3h of residence time for 3100mg l À1phenol feed concentration (current density:54.7mA cm À2;T :251C;electrolyte concentration:120g l À1).B.K.K .orbahti,A.Tanyola -c /Water Research 37(2003)1505–15141510dioxide anode packed-bed reactor.In their work,the energy requirement changedfrom4.8to2.4kWh molÀ1 phenol removedas the initial phenol concentration increasedfrom525to1100mglÀ1in batch runs.Chettiar andWatkinson[11]achieved95.8%phenol removal for 1070mg lÀ1initial phenol concentration after5h at10A with an electrochemical system adapted from the previous work of Smith de Sucre and Watkinson[3]. Sharifian andKirk[21]achievedalmost100%phenol removal within6h for1316mg lÀ1initial phenol concentration in1M H2SO4at a cell current of2A at 251C and1ml sÀ1flow rate with a packed-bed reactor of PbO2pellets.Nevertheless,after10h of reaction time, the intermediates of maleic acid and benzoquinone were still in the medium.Gattrell and Kirk[2]achievedabout 60%,60%and55%phenol removal for470,940and 1880mg lÀ1initial phenol concentrations,respectively, at 1.7V in8h of electrolysis time with aflow-by electrochemical cell.For all three concentrations,the rate of phenol removal slowedd own after thefirst hour due to formation of greater amounts of intermediates. The authors also reportedthat phenol passivatedthe electrode surface during thefirst hour of operation due to the polymer forming reaction.K.otz et al.[18] achievedcomplete phenol removal after2A h charge passedfor1000mg lÀ1phenol concentration by anodic oxidation using a SnO2anode at30mA cmÀ2current density.The authors reported that after1A h charge passed;the phenol disappeared while the complete removal of TOC took about8A h andcalculatedthe energy requirement as 1.88kWh molÀ1of phenol ninellis and Pulgarin[12]achieved100% TOC removal at70Ah dmÀ3with SnO2anodes for 1974mg lÀ1initial phenol concentration,for701C and 50mA cmÀ2current density with a two-compartment electrochemical cell.Again,Comninellis andNerini[13] achievedcomplete phenol removal at15A h d mÀ3for 940mg lÀ1initial phenol concentration in the presence of NaCl,for501C,25.3g lÀ1NaCl concentration and 100mA cmÀ2current density using an electrochemical system adapted from the previous work of Comninellis andPulgarin[12]with Ti/SnO2anodes to oxidize phenol anodically.Lin et al.[20]achieved70%COD removal within60min for1000mg lÀ1initial phenol concentra-tion with60mg lÀ1H2O2addition at2.5A current and 1%of salinity using a batch system with four pieces of cast iron cathode and anode.The authors also reported that the COD removal without H2O2addition at the same conditions was34%.Alvarez-Gallegos and Pletch-er[36]andHarrington andPletcher[37]investigatedthe electrochemical removal of low-level organics including phenol.Alvarez-Gallegos andPletcher[36]calculated the energy reqirement for0.33mM phenol solution as 1.25kWh mÀ3to reduce the COD to o10ppm.Har-rington andPletcher[37]reportedthat the energy consumptions for the treatment of1m3of the0.5mM phenol solution assuming a cell voltage of5V liedin the range 1.5–2.5kWh mÀ3which was low comparedto other electrochemical alternatives for the removal of organics from wastewater.The authors also calculated the energy consumption for the teatment of3mM phenol solution around14kWh mÀ3.After reaching steady state,our continuous tubular reactor residence time values for almost complete phenol removal,40min and3h for450and3100mg lÀ1phenol feedconcentrations,respectively,are less than those of literature for electrochemical treatment,andthe treat-ment also requires less specific energy, 2.679and 6.379kWh molÀ1phenol consumedfor450(40min) and3100mg lÀ1(3h)phenol feedconcentrations, respectively;denoting a feasible alternative reactor configuration.This advantage is partially due to the reactor type and also due to a different reaction mechanism,which favouredthe fast formation of non-passivating polymeric endprod ucts rather than slow total oxidation of phenol.3.2.Determination of conversion productsGC/MS chromatograms andmass spectrums were obtained in order to identify the intermediate products formedin the liquidphase d uring the electrochemical conversion of phenol.The data in F igs.6and7were collectedin batch runs carriedout at32.9mA cmÀ2,Table2The energy requirement andelectron consumption rate for3100mg lÀ1phenol feedconcentration(current density:54.7mA cmÀ2;T: 251C;electrolyte concentration:120g lÀ1)Residence time (h)Timerequiredtoreachsteady state(h)Phenolconsumptionrateat steady state(mmol hÀ1)Specific energyrequirement at steadystate(kWh molÀ1phenolconsumed)Electronconsumptionrateat steady state(mol eÀhÀ1)Phenolremoval(%)atsteady state1526.7882 4.3450.24421.5530.1899 4.6700.29712525.8315 5.7040.26813520.8353 6.3790.2898B.K.K.orbahti,A.Tanyola-c/Water Research37(2003)1505–15141511251C reaction temperature and120g l À1electrolyteconcentration for 496and3505mg l À1initial phenol concentrations.In F igs.6and7,concentrations of all compounds were expressed as percentage weight of initial phenol present in the waste stream.For each batch run the exit stream was completely recycledwith the flow rate of 6000ml min À1andfedto the inlet of the column.From periodic analysis of the medium taken at the exit,it was understood that mainly mono,di-and tri-substitutedchlorinatedphenol prod ucts were formed during the electrolysis and consumed thereafter by either destruction or polymerization,or both as seen in Figs.6and7.Diverse from literature [2,3,9–12,14,15,21,23]except the work of Comninellis andNerini [13],only chlori-nated phenol products formed during the runs with Cl 2gas discharging on the anode;and all the chlorinated phenol derivatives were completely consumed either by destruction or polymerization at 496and 3505mg l À1initial phenol concentrations after 120min and11h,respectively.As LundandIverson [38]previously stated,the oxidation of organic compounds at graphite anode often results in other products when considered with the oxidation at platinum anode,but in our work we had only four different intermediates,which did not turn into successive intermediate compounds in contrast to other studies of literature [2,3,9–12,14,15,21,23].Firstly,4-chlorophenol and2,4,6-trichlorophenol formed dominantly during the electrolysis and followed by 2-chlorophenol andthen 2,4-d ichlorophenol for both initial phenol concentrations of 496and3505mg l À1.In Fig.6for 496mg l À1initial phenol concentration,the weight percentage of 2,4,6-trichlorophenol increased rapidly up to 40min,although 4-chlorophenol started to decrease after 20min.The weight percentage of polymeric compounds increased significantly after 40min with the disappearance of mono,di and tri-chlorophenols.This result showedthat the chlorinated hydrocarbons contributed to the formation of polymeric structure at a certain extent,while part of them might be oxidized.Finally,after 120min,no intermediates were left in the reaction medium at all.Due to the contribution of chlorine into the polymer structure for 450mgl À1phenol feedconcentration,the final weight percentage of polymeric compounds passed over 100%[39].020406080100120020406080100120Elapsed Time (min)C o m p o u n d % (w /w )Fig.6.The weight percentage of conversion products based on initial phenol at 496mg l À1initial phenol concentration in the batch run (32.9mA cm À2current density,251C reaction temperature,120g l À1electrolyte concentration).0102030405060708090100081012Elapsed Time (h)C o m p o u n d % (w /w)246Fig.7.The weight percentage of conversion products based on initial phenol at 3505mg l À1initial phenol concentration in the batch run (32.9mA cm À2current density,251C reaction temperature,120g l À1electrolyte concentration).B.K.K .orbahti,A.Tanyola -c /Water Research 37(2003)1505–15141512。