外文原文-电化学改良城市污水的生物降解.pdf

Biochemical Engineering Journal 22 2005 239 244 Electro chemically improved bio degradation of municipal sewage Lehua Zhanga Jinping Jiaa Youchun Zhub Nanwen Zhua Yalin Wanga Ji Yanga a School of Environmental Science and Engineering Shanghai Jiaotong University Shanghai 200240 PR China b School of Environmental Science and Engineering Guangdong University of Technology Guangzhou 510090 PR China Received 26 March 2004 received in revised form 27 September 2004 accepted 28 September 2004 Abstract Biofi lm electrode reactor and activated sludge electrode reactor were developed based on biofi lm reactor and activated sludge reactor The effect of electro chemical reaction on the bio degradation of municipal sewage was examined by the comparison experiments Denitrifi cation was improved by combining biofi lm process with electro chemical effect in a single novel reactor and sludge bulking was compacted for the introduction of electrode in activated sludge system 2004 Elsevier B V All rights reserved Keywords Biodegradation Wastewater treatment Biofi lms Activated sludge Bio electro reactor Denitrifi cation Municipal sewage 1 Introduction It is very important to remove nutrients suffi ciently from wastewater as well as organic matter Nitrogenous com pounds are the principal nutrients in wastewater effl uents Denitrifi cationwasaccomplishedinanovelbio electroreac tor by several researchers 1 2 The enzymes were fi xed to the surface of the cathode while a low voltage was applied resulting in two stage nitrate reduction to N2via nitrite 1 Then denitrifying microorganisms were immobilized on a carbonelectrodeandthehydrogenproducedthroughtheelec trolysis of water was utilized for the reduction of nitrate to N2 2 4 A combined heteratrophy electrode biofi lm reac tor was developed for nitrate removal from ground water and the denitrifi cation capacity of the reactor was 10 7gNO3 N m3h 1 5 Someinvestigationsontheremovalofvariouscontamina tions using bio electro reactors have been carried out It was confi rmed that COD as well as nitrate was removed simul taneously and that endogenous denitrifi cation may occur as Corresponding author Tel 86 21 54742817 E mail addresses zhanglehua L H Zhang jpjia J P Jia qshli Y C Zhu Tel 86 20 37628949 well as denitrifi cation supported by hydrogen used as elec trondonor 6 Simultaneousremovalofnitrateandpesticide 7 copper ion 8 or ammonium nitrogen 9 11 was ap provedbyusingabio electro chemicalreactor However the study on the removal of other contaminations is quite limited 12 In this study the electrode system was introduced into biofi lm reactor and activated sludge reactor The effect of the electro chemical reaction on bio degradation of mu nicipal sewage was evaluated by the comparison experi ments and the effect of electric current on the removal of contaminations was investigated in the biofi lm electrode reactor 2 Materials and methods 2 1 Experimental set up and operation Fig 1showsaschematicdiagramofthebiologicalreactors and bio electro reactors used in this study Biofi lm electrode reactor and activated sludge electrode reactor were devel oped based on biofi lm reactor and activated sludge reactor Every reactor consisted of a cylinder with an i d of 19 5cm and a height of 15 1cm In addition there were two sludge 1369 703X see front matter 2004 Elsevier B V All rights reserved doi 10 1016 j bej 2004 09 016 10 L Zhang et al Biochemical Engineering Journal 22 2005 239 244 Fig 1 Schematic diagram of the experimental apparatus 1 activated sludge reactor 2 activated sludge electrode reactor 3 biofi lm reactor 4 biofi lm electrode reactor 5 feed tank 6 sampling port 7 peristaltic pump 8 secondary sedimentation tank 9 air pump 10 air fl owmeter 11 surplus sludge 12 dc power supply recycling systems working for activated sludge reactor and activated sludge electrode reactor respectively Activated sludge reactor and activated sludge electrode reactor were completely mixed Activated sludge electrode reactor was the same as activated sludge reactor except elec trode was introduced The one central anode was graphite which was 3 0cm o d Twelve surrounding cathodes were stainless steel which were 2 5cm wide 15 0cm long and 2mm thick The cathodes were 450cm2in total area In the biofi lm electrode reactor and biofi lm reactor the biofi lm carrier material was the admixture of granular acti vatedcarbon GAC andporcelainballwith3 4mmo d The mixing ratio of GAC and porcelain ball was 7 3 The cen tral anode and surrounding cathodes of the biofi lm electrode reactor was the same as that of activated sludge electrode reactor Tables 1 and 2 show the characteristics of the wastewater and the experimental conditions in this study respectively The real wastewater was municipal sewage in Guangzhou city a south city of China Peristaltic pumps Model BT00 100M Gelan Co Ltd PR China regulated the fl ow of wastewater and the hydraulic retention time HRT was 6h The fl ow was measured by a fl owmeter Model LZB 4 Experiments were conducted at 20 25 C and the dis solved oxygen in reactors was 1 8 2 5mgL 1 In the acti vated sludge electrode reactor and activated sludge reactor the sludge return ratio r was 100 and the mixed liquor Table 1 Characteristics of infl uent wastewater pH6 5 7 5 CODCr mgL 1 140 325 BOD5 mgL 1 80 300 NH3 N mgL 1 15 1 38 0 Total nitrogen mgL 1 37 2 68 0 Total phosphorus mgL 1 2 2 5 7 SS mgL 1 70 300 suspended solids MLSS was 1 90 2 00gL 1 In order to maintain the biofi lm reactor and biofi lm electrode reactor in optimum working conditions we carried out backwash ing every 24h During the backwashing the air and wa ter fl ows were 0 45m3 m2min 1of water for 3min and 0 75m3 m2min 1 ofairfor6min Thefi xedelectriccurrent wasappliedtobiofi lm electrodereactorandactivatedsludge electrode reactor by two dc power apply Model GPS5010H Shanghai Songta Electric Co Ltd PR China respectively The digital multimeter Model DM 6335 Shanghai Preci sion T 20 25 C r 100 a TSS for biofi lm reactor and biofi lm electrode reactor MLSS for activated sludge reactor and activated sludge electrode reactor 2 3 Different electric current experiments The effect of electric current on the removal of contami nations by the biofi lm electrode reactor was examined The electric current intensity varied between 20 and 120mA and the details of conditions were showed in Table 2 Electric currents were at 20 40 60 80 100 and 120mA with the averaged DO of 2 1 2 1 2 2 2 2 2 2 and 2 4mgL 1as well as the biomass concentration of 5 86 5 84 5 83 5 79 5 82 and 5 80gTSSL 1 respectively A week period of adapta tiontovarietyofelectriccurrentwasrequiredtoensurestable operation 2 4 Analytical methods Watersamplesfortheanalysiswerecentrifuged 2000rpm 15min and G force at 6 96kms 2 Model XTL 5 0 Shanghai Centrifuge Institute PR China to separate the sludge Thedissolvedoxygenconcentrationwasmeasuredby a YSI Model 58 oxygen meter Yellow Springs Instrument Co Inc The pH was measured using a pH meter Model 260A Shanghai Precision the averaged biomass concentrations were 5 81 and 5 83gTSSL 1as well as the averaged DOs were 2 0 and 2 2mgL 1in biofi lm reactor and biofi lm electrode reactor respectively 12 L Zhang et al Biochemical Engineering Journal 22 2005 239 244 Fig 3 Schematic diagram of micro environment theory anodic reaction and aerobic environment cathodic reaction and anaerobic environment The second is micro environment theory It was proved that electro chemical reaction taken place on the particle elec trode in the three dimensional electrolytic cell that was packed with activated carbon 15 17 Anode reaction and cathode reaction could take place on the different side of ac tivated carbon 15 16 respectively The local heterogene ity could exist though the bulk was complete mixed in the biofi lm electrode reactor The anode reaction produces highly oxidative substances and the cathode reaction pro duces highly deoxidizing substances The ORP around cath ode was 150 300mV lower than that around anode The detailed information will be reported in another paper The anaerobic environment can exist around cathode for the ca thodic reaction and aerobic environment can exist simul taneously around anode for the anodic reaction and aera tion Fig 3 16 20 The denitrifying microorganisms were enriched 17 in the cathodic area The denitrifi cation was enhanced for the alternation of different environment and enrichment of denitrifying microorganisms However these mechanismsofelectrolyticallyenhancedremovaldonotclear and further studies are needed to confi rm the cooperation of electrode and microbe Table 3 shows the property of activated sludge in acti vated sludge reactor and activated sludge electrode reactor The mixed liquor suspended solids MLSS were 1 92 and 1 95gL 1in activated sludge reactor and activated sludge electrode reactor respectively The sludge volumetric index Table 3 Propertyofactivatedsludgeinactivatedsludgereactorandactivatedsludge electrode reactor Activated sludge reactor Activated sludge electrode reactor Activated sludge MLSS gL 1 1 921 95 SVI mL 12293 Total bacteria count mL 1 6 4 1077 1 107 Vorticella mL 1 8 8 1021 0 103 Filamentous microorganismsMoreLess Effl uent Free cells count mL 1 3 3 1052 1 105 Electric current 60mA DO 2 2mgL 1 SVI was 122 and 93mL in activated sludge reactor and ac tivated sludge electrode reactor respectively The difference of SVI is signifi cant The electro chemical reaction or elec tric fi eld improved sludge settling characteristics Vorticella was8 8 102and1 0 103mL 1inactivatedsludgereactor and activated sludge electrode reactor respectively The fi la mentous microorganisms were more in activated sludge than inelectrode activatedsludgethroughtheopticalmicroscope The total bacteria count was 6 4 107and 7 1 107mL 1 in activated sludge reactor and activated sludge electrode re actor respectively The number of free cells in the effl u ent was 3 3 105and 2 1 105mL 1in activated sludge reactor and activated sludge electrode reactor respectively Since the potential of activated sludge decreased with the electric fi eld intensity or electro chemical reaction and electrical double layer might be compressed bulking sludge was compacted in the activated sludge electrode reactor Fig 4 shows the removal of contaminations in activated sludgereactorandactivatedsludge electrodereactor There moval of CODCr NH3 N total nitrogen of activated sludge electrode reactor were 1 0 3 0 and 0 6 more than that of activated sludge reactor Their standard deviations were 3 6 3 6 5 9 for activated sludge reactor and 2 7 3 6 4 0 for activated sludge electrode reactor respectively The re moval of organic and nitrogenous contamination was not af fectedsignifi cantlybytheelectro chemicalreactionintheac tivatedsludge electrodereactor Sincethewastewaterisgood at biodegradability the microorganism achieved the removal of organic contamination not by the electrolysis There may be two reasons why biological reductions of nitrate through the use of H2at the cathode were not observed in this reac tor The fi rst reason is that both of activated sludge electrode reactor and activated sludge reactor were completely mixed reactors in which the wastewater mixed quickly with high dissolvedoxygenconcentration DO 2 0 2 5mgL 1 The second reason is that the activated sludge was not immobi lized on a cathode electrode and it is diffi cult to use H2at the cathode for dentrifying microorganisms Table4showstheremovalsofBOD5infourdifferentreac tors The removals of BOD5were 94 6 94 8 93 9 and 94 3 in biofi lm reactor biofi lm electrode reactor activated Fig 4 Results of activated sludge reactor and activated sludge electrode reactor electric current 60mA the averaged MLSSs were 1 93 and 1 95gL 1as well as the averaged DOs were 2 2 and 2 3mgL 1in acti vated sludge reactor and activated sludge electrode reactor respectively 13 L Zhang et al Biochemical Engineering Journal 22 2005 239 244 Table 4 Removal of BOD5in the four different reactors BOD5 mgL 1 Removal of BOD5 Removal of CODCr Infl uent157 Effl uent Biofi lm reactor8 494 690 3 Biofi lm electrode reactor8 194 892 8 Activated sludge reactor9 593 988 5 Activated sludge electrode reactor9 094 389 5 Electric current 60mA DO 2 2mgL 1 biomass concentration 5 83 and 5 87gTSSL 1 in biofi lm reactor and biofi lm electrode reactor MLSS 1 92 and 1 95gL 1in activated sludge reactor and activated sludge electrode reactor Fig 5 Results of different electric current experiments electric current at 20 40 60 80 100 and 120mA with the averaged DO of 2 1 2 1 2 2 2 2 2 2 and 2 4mgL 1as well as the biomass concentration of 5 86 5 84 5 83 5 79 5 82 and 5 80gTSSL 1 respectively sludgereactorandactivatedsludge electrodereactor respec tively Thedifferenceisnotsignifi cant Sothebiodegradation oforganiccontaminationswasnotenhancedapparentlyinthe experiment 3 2 Different electric current experiments The results of the different reactors experiments indi cated that the denitrifi caion was enhanced by the coopera tionofelectrodeandmicrobeinthebiofi lm electrodereactor Fig 2 Fig 5 shows the results of different electric current experiments in the biofi lm electrode reactor The removal of CODCrand NH3 N were not affected signifi cantly when the electricalcurrentintensitywaslessthan120mA thevoltages were 7 31 7 58V and the average was 7 45V The removal of total nitrogen increased as the electrical current intensity wentupto80mAandthendecreasedwhentheelectricalcur rent intensity was higher than 80mA A peak of the removal of total nitrogen was up to 75 at 80mA It was proved that the electrical current was benefi cial to denitrifi cation at lower electrical current intensity and the denitrifi cation was adversely affected at higher electrical current intensity in the biofi lm electrode reactor 4 Conclusions Biofi lm electrode reactor and activated sludge electrode reactor were developed based on biofi lm reactor and acti vated sludge reactor The effect of electro chemical reaction on bio degradation of municipal sewage was examined by thecomparisonexperiments Thefollowingconclusionswere obtained in this study In biofi lm electrode reactor the denitrifi cation was en hanced for the cooperation of electrode and microbe at lower electricalcurrentintensity e g 60mA andtheelectricalcur rent was not benefi t to denitrifi cation at higher electrical cur rentintensity e g 120mA Inactivatedsludge electrodere actor theelectro chemicalreaction orelectricfi eld waspos itiveforcompactingbulkingsludge However theremovalof organicandnitrogenouscontaminationswasnotaffectedsig nifi cantly by the electro chemical reaction or electric fi eld The differences in biodegradation of organic contaminations between the biological reactor and the bio electro reactor were not statistically signifi cant in this study Acknowledgement This study was supported in part by the 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