Electric power generation from treatment of food waste leachate using microbial fuel cell

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1 Environ. Eng. Res. 2017; 22(2): pissn eissn X Electric power genertion from tretment of food wste lechte using microil fuel cell Ze Jie Wng 1,2, Bong Su Lim 1 1 Deprtment of Environmentl Engineering, Dejeon University, Dejeon 34520, Repulic of Kore 2 Qingdo Institute of Bioenergy nd Bioprocess Technology, Chinese Acdemy of Sciences, Qingdo , Chin ABSTRACT Simultneous tretment of food wste lechte nd power genertion ws investigted in n ir-cthode microil fuel cell. A TCOD removl efficiency of 95.4 ± 0.3% ws chieved for n initil COD concentrtion of 2,860 mg/l. Mximum power density rnged ws mximized t 1.86 W/m 3, when COD concentrtion vried etween 60 mg/l nd 2,860 mg/l. Menwhile, columic efficiency ws determined etween 1.76% nd 11.07% for different COD concentrtions. Cyclic voltmmetric dt reveled tht the oxidtion pek voltge occurred t V, shifted to out V. Moreover, reduction pek voltge t V ppered when orgnic mtters were exhusted, indicting tht reducile mtters were produced during the decomposition of orgnic mtters. The results showed tht it ws fesile to use food wste lechte s fuel for power genertion in microil fuel cell, nd the tretment efficiency of the wstewter ws stisfied. Keywords: COD removl, Electric power genertion, Food wste lechte, Microil fuel cell 1. Introduction During the collection nd tretment processes of food wste, lrge quntity of lechte would produce. In Kore, for exmple, it ws reported s 9,077,000 kg/d in 2007, which ws predicted to increse to 12,227,000 kg/d y 2013 [1]. One of tretment strtegies for food wste lechte is to dischrge it into civil wstewter tretment plnts [1]. The strtegy cn increse the opertionl cost, nd wste vlule energies crried y orgnic mtters nd nutrient contents in the food wste lechte. Tremendous ttentions hve een pid to microil fuel cells (MFCs). MFCs could ttrct electric energy from orgnic mtters, nd thus they re promising technology to provide green energy nd clen wstewter [2]. Exoelectrogens re with the ility to trnsfer electrons intrcellulrly to externl electron cceptor, nd thus they ply core role of trnsferring electrons ttrcted from degrdtion of orgnic mtter to the ndic surfce to close the process of electric power genertion. Becuse of the extrcellulr electron trnsfer process, MFCs could ccelerte the removl efficiency of orgnic mtters nd even they re le to degrde some persistence orgnic pollutnts [3]. Severl kinds of rel orgnic wstewter were successfully treted with MFC technology. Lndfill lechte is high strength wstewter. In ir-diffusion cthode MFC, 8.5 kg COD m -3 d -1 ws removed nd 344 mwm -3 electric power ws generted [4]. Similr tretment efficiency ws determined to other kinds of high strength wstewters, including swine wstewter [5], fermented wstewter [6], rewery wstewter [7, 8], nd strch processing wstewter [9]. Food wste lechte contins rich orgnic mtters, such s proteins nd lcohol, nd thus it should e n lterntive sustrte for power genertion in MFCs. However, the fesiility of food wste lechte s sustrte for power genertion in MFCs hs not yet een reported. The purpose of the present study, therefore, is to evlute the possiility of using food wste lechte s sustrte for MFCs, nd determine the removl efficiency of orgnic mtters. Moreover, the performnce of MFCs responding to initil COD concentrtion ws s well compred. 2. Mterils nd Methods 2.1. MFC Friction The volume of the ir-diffusion cthode MFC ws 234 ml (6.5 cm 6 cm 6 cm), with n effective volume of 200 ml (Fig. 1). This is n Open Access rticle distriuted under the terms of the Cretive Commons Attriution Non-Commercil License ( which permits unrestricted non-commercil use, distriution, nd reproduction in ny medium, provided the originl work is properly cited. Copyright 2017 Koren Society of Environmentl Engineers Received My 1, 2016 Accepted Novemer 21, 2016 Corresponding uthor Emil: slim@dju.kr Tel: Fx:

2 Ze Jie Wng nd Bong Su Lim The food wste lechte ws diluted to different initil COD concentrtions with distilled wter, nd then uffered with 1.5 g/l KH 2 PO 4 nd 2.2 g/l K 2 HPO 4. Cyclic voltmmogrm (CV) nlysis ws crried out with three-electrode configurtion with node s working electrode, cthode s counter electrode nd Ag/AgCl (3.3 M KCl) s reference electrode. The MFC ws performed vi tch mode nd the nodic solution ws stirred with mgnetic stirring r. During the reserch, the temperture ws controlled t 30 ± 1 o C in n incutor Clcultions Fig. 1. Schemtic of the ir-cthode MFC rector. The node ws mde of cron felt with geometricl surfce re of 49.6 cm 2, nd the cthode ws commercilly ville ELAT gs diffusion electrode (Lot #LT 120E-W: ) with Pt ctlyst (20%). Nfion 115 memrne (Alfr, USA) ws pretreted s previously descried [10]; then het pressed to the ctlyst side of the cthode t 120 o C. The memrne side ws set to fce the nodic solution. Titnium wire ws used to connect node nd cthode MFC Inocultion nd Opertion The inoculum ws collected from the Okchen wstewter tretment plnt (Okchen, Kore). To strt up the MFC, 20 ml inoculum ws mixed with 180 ml of rtificil wstewter contining 1.05 g/l NH 4 Cl, 1.5 g/l KH 2 PO 4, 2.2 g/l K 2 HPO 4, 0.2 g/l yest extrct, nd 1.36 g/l CH 3 COON 3H 2 O s electron donors [11]. When the voltge decresed elow 30 mv, 0.3 g CH 3 COON 3H 2 O ws dded to the nodic solution until consecutive stle voltges were chieved t lest twice. After the MFC ws successfully inoculted, the solution ws replced with food wste lechte. The food wste lechte ws kept t 4 o C in refrigertor, nd its chrcteristics were listed in Tle 1. Tle 1. Chrcteristics of Food Wste Lechte Prmeters Vlue COD, mg/l 29,120 ± 120 ph 4.94 ± 0.01 SS, mg/l 1,920 ± 80 TN, mg/l ± 28.2 TP, mg/l ± 6.9 NH 3 -N, mg/l ± 2.36 Conductivity, ms/cm ± 0.08 Slinity, ppt 5.5 ± 0.0 t 32.7 ± 0.3 C Both voltge nd CV were recorded with pertentiostt (WMPG 1000, Won-A Tech, Kore). Power density (W/m 3 ) were clculted ccording to P = V 2 /R v, where V is the voltge cross the externl resistnce (R), nd v is the effective volume of node chmer. Current nd current density were clculted s I = V/R nd J = I/v, respectively. Coulomic efficiency (CE) ws clculted s CE = C P /C T, where C P is the prcticl couloms clculted y integrting the current over time, nd C T is the theoreticl couloms ville from removed COD. The internl resistnce (R int ) ws determined s the slope of I-V curve ccording to V = E-I R int, where E is electromotive force of the cell [12]. 3. Results nd Discussion 3.1. Voltge Output With sodium cette s n electron donor, stle voltge of out 390 mv cross the externl resistor ws repetedly otined (Fig. 2(), ltest 3 cycles). Replcing rtificil wstewter with food wste lechte, the voltge rose quickly to stle voltge of 270 mv (Fig. 2()). The results demonstrted tht orgnic components of food wste lechte were esily decomposed y exoelectrogens locted on the surfce of node. After complete cycles, the TCOD decresed from 2,860 mg/l to ± 8.6 mg/l, representing removl efficiency of 95.4 ± 0.3%. The SCOD decresed y 96.2 ± 0.6% from 2,664 mg/l to ± 15.6 mg/l. The CE ws used to indicte the recovery efficiency of electrons s electric current from the decomposition of orgnic mtters. It ws determined tht the CE ws 5.79 ± 0.03% in the present study. It ws similr to 6.7% to 8% with strch processing wstewter s fuel for MFC [9], however, it ws lrger thn tht (< 1%) when fermented wstewter ws used for power genertion [6]. Low CE indicted tht lrge mount of electrons contining in orgnic mtters ws consumed y processes other thn power output. Within the electroctive iofilm, mny other species of microorgnism thn exoelectrogens exit, such s methnogenium [6]. The methnogenium could compete with exoelectrogens to tke dvntge of the orgnic mtters to produce methne insted of electric current, nd thus decresing the CE of MFCs. Moreover, the environment of ir-diffusion cthode MFC is not definitely neroic, nd thus orgnic mtters could e eroiclly degrded y microorgnism, which could s well reduce the CE [13]. For COD of 2,860 mg/l, mximum power density ws determined s 1.53 ± 0.11 W/m 3 t current density of 8.75 ± 0.31 A/m 3 (Fig. 3()). It ws similr to 1.10 W/m 3 for rel field 158

3 Environmentl Engineering Reserch 22(2) Fig. 2. Voltge output during the strt-up period () nd food wste lechte s fuel () (externl resistor of 500 Ω). Fig. 3. Power densities t different current densities () nd I-V curve () (externl resistnce from 1,000 Ω to 50 Ω, duplicte dt). diry wstewter [14], 2.19 W/m 3 for niml crcss wstewter [15], nd 2.21 W/m 3 for se food processing wstewter s fuel [16], ut it ws smller thn 8.0 W/m 3 for rel dye wstewter [17]. Moreover, the R int ws determined s ± 3.95 Ω (Fig. 3()). Performnce of MFCs relies on couples of fctors, such s the configurtion, electrode mteril, opertion prmeter, nd chrcteristics of the rel wstewter [18]. The nture of wstewter would ffect the community composition of the electroctive iofilm, nd further influence the wstewter tretment efficiency nd electric power genertion [19] Effects of COD Concentrtion COD concentrtion could ffect the performnce of MFCs. Different COD concentrtions (60, 110, 275, 580, 878, 2,160, nd 2,860 mg/l) were used to evlute its influence on the electric power genertion, R int, nd CE. The solutions were uffered with 1.5 g/l KH 2 PO 4, nd 2.2 g/l K 2 HPO 4. The mximum power density rnged etween 1.19 ± 0.04 nd 1.86 ± W/m 3 for different initil COD concentrtions (Fig. 4()). It ws est fitted to the BoxLucs 1 model using OriginPro 7.5 progrm (R 2 = 0.973) ccording to the eqution: P = P mx (1-e -kcs ), where k is the growth rte constnt, nd Cs is the sustrte concentrtion. It ment tht the mximum power density could e esily otined even t reltively low concentrtion of orgnic mtter. At COD concentrtion of 580 mg/l, the lrgest mximum power density (1.86 ± W/m 3 ) ws otined due to the smllest R int of 83.7 ± 0.3 Ω (Fig. 4()). R int ws clculted to e etween 83.7 ± 0.3 nd ± 1.55 Ω for different initil COD concentrtions. Bsed on the sme uffer concentrtion, high COD concentrtion (low dilution rtio) led to high solution conductivity, nd n increse in solution conductivity would lower the R int of MFC [12]. However, such reltion etween conductivity nd R int ws only oserved when the COD concentrtion ws not lrger thn 580 mg/l. Lrger COD concentrtion thn 580 mg/l led to lrger R int. The reson for this might e tht the concentrtion 159

4 Ze Jie Wng nd Bong Su Lim Fig. 4. Mximum power density () nd internl resistnce () for different COD concentrtions (duplicte dt). Tle 2. Comprison of CE for Different COD Concentrtion COD (mg/l) Coulom (C) Coulomic Influent Effluent Removed Generted Recovered Efficiency (%) 2,160 1,562.1 ± ± 3.7 1, ± ± ± ± ± , ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± of possily existing hrmful mtters ws high enough to limit the ctivity of exoelectrogens with low dilution rtio. CE could e s well ffected y the COD concentrtion. In the present study, the CE incresed from 9.64% for COD of 60 mg/l to ± 1.51% for COD of 110 mg/l, nd then decresed to 1.76 ± 0.06% for COD of 2,160 mg/l (Tle 2, sed on 12 h dischrge). The inverse reltionship etween CE nd COD concentrtion ws lso oserved y other reserch [5]. It ws ecuse tht higher COD concentrtion took longer time to e completely decomposed y microorgnism, nd therefore more oxygen could diffuse to the nodic chmer; more oxygen could provide more electron cceptors for eroic microorgnism to consume the orgnic mtters, which further decresed the CE [5]. Bsed on the sme rection time in this study, hrvested coulom ws not significntly different when the COD ws sturted. However, removed COD ws positively correlted to initil COD, which led to low CE for high initil COD. It ws implied tht other fctors esides to oxygen diffusion tht could lower CE should e tken into considertion to improve CE when rel wstewter ws used to generte electric power in MFCs Cyclic Voltmmetry The Cyclic Voltmmetry (CV) for initil nd treted food wste lechte were performed with n initil COD of 580 mg/l (Fig. 5). Oviously, n oxidtion pek ws oserved for the originl food wste lechte t out V. After the MFC cycle ws complete, the oxidtion pek decresed in intensity nd shifted to out V. Fig. 5. CVs for initil nd rected solutions with n initil COD of 580 mg/l (scn rte of 50 mv/s). The decrese in the oxidtion pek ws possily due to the decomposition of orgnic mtters y the microes, which further led to sustrte limittion to the exoelectrogens. When the orgnic mtter ws decomposed, however, the reduction current ws incresed nd current pek ppered t out V. The incresed reduction current in the CV curve ws likely incurred y the produced reducile mtters during the decomposition process of orgnic mtters. Moreover, the pek current voltge of V ws lrger thn previously reported voltge of V for NAD+/NADH [20]. It is implied tht the electroctivity of the 160

5 Environmentl Engineering Reserch 22(2) iofilm in the present ws more roust, proly due to tht some exoelectrogens within the iofilm otined high ility to trnsfer electrons from the microe to the nodic surfce. 4. Conclusions In the present reserch, electric power genertion coupled with food wste lechte tretment using ir-diffusion cthode MFC ws successfully studied. The removl efficiency of COD ws determined to e s high s 95.4 ± 0.3%, when the COD concentrtion ws 2,860 mg/l. The mximum power density rnged ws mximized t 1.86 W/m 3, with COD concentrtion rnged of 60-2,860 mg/l. CV experiments showed tht reducile mtters were produced during the process of food wste lechte decomposition nd implied tht exoelectrogens with high ility to trnsfer electrons existed within the iofilm on the node. References 1. Koren Ministry of Environment. Study on development on optimum models nd fcilitting/opertionl guide line ccording to methods for energy genertion of food wste nd lechte. Sejong: Ministry of Environment; Wng Z, Lee T, Lim B, Choi C, Prk J. Microil community structures differentited in single-chmer ir-cthode microil fuel cell fueled with rice strw hydrolyste. Biotech. Biofuels 2014;7:9. 3. Wng L, Liu Y, M J, Zho F. Rpid degrdtion of sulphmethoxzole nd the further trnsformtion of 3-mino-5-methylisoxzole in microil fuel cell. Wter Res. 2016;88: Puig S, Serr M, Com M, Cré M, Blguer MD, Colprim J. Microil fuel cell ppliction in lndfill lechte tretment. J. Hzrd. Mter. 2011;185: Min B, Kim JR, Oh SE, Regn JM, Logn BE. Electricity genertion from swine wstewter using microil fuel cells. Wter Res. 2005;39: Nm JY, Kim HW, Lim KH, Shin HS. Effects of orgnic loding rtes on the continuous electricity genertion from fermented wstewter using single-chmer microil fuel cell. Bioresour. Technol. 2010;101: Wen Q, Wu Y, Co DX, Zho LX, Sun Q. Electricity genertion nd modeling of microil fuel cell from continuous eer rewery wstewter. Bioresour. Technol. 2009;100: Wng X, Feng YJ, Lee H. Electricity production from eer rewery wstewter using single chmer microil fuel cell. Wter Sci. Technol. 2008;57: Lu N, Zhou S-G, Zhung L, Zhng J-T, Ni J-R. Electricity genertion from strch processing wstewter using microil fuel cell technology. Biochem. Eng. J. 2009;43: Che KJ, Choi MJ, Ajyi FF, Prk WS, Chng IS, Kim IS. Mss trnsport through proton exchnge memrne (Nfion) in microil fuel cells. Energ. Fuel. 2008;22: Rmsmy RP, Ren ZY, Mench MM, Regn JM. Impct of initil iofilm growth on the node impednce of microil fuel cells. Biotechnol. Bioeng. 2008;101: Liu H, Cheng SA, Logn BE. Power genertion in fed-tch microil fuel cells s function of ionic strength, temperture, nd rector configurtion. Environ. Sci. Technol. 2005;39: Cheng SA, Liu H, Logn BE. Incresed performnce of single-chmer microil fuel cells using n improved cthode structure. Electrochem. Comm. 2006;8: Mohn SV, Mohnkrishn G, Velvizhi G, Bu VL, Srm PN. Bio-ctlyzed electrochemicl tretment of rel field diry wstewter. Biochem. Eng. J. 2010;51: Li X, Zhu N, Wng Y, Li P, Wu P, Wu J. Animl crcss wstewter tretment nd ioelectricity genertion in up-flow tuulr microil fuel cells: Effects of HRT nd non-precious metllic ctlyst. Bioresour. Technol. 2013;128: Jyshree C, Tmilrsn K, Rjkumr M, et l. Tretment of sefood processing wstewter using upflow microil fuel cell for power genertion nd identifiction of cteril community in nodic iofilm. J. Environ. Mnge. 2016;180: Klthil S, Lee J, Cho MH. Efficient decoloriztion of rel dye wstewter nd ioelectricity genertion using novel single chmer iocthode-microil fuel cell. Bioresour. Technol. 2012;119: Rinldi A, Mecheri B, Grvgli V, Licocci S, Di Nrdo P, Trvers E. Engineering mterils nd iology to oost performnce of microil fuel cells: A criticl review. Energy Environ. Sci. 2008;1: Che KJ, Choi MJ, Lee JW, Kim KY, Kim IS. Effect of different sustrtes on the performnce, cteril diversity, nd cteril viility in microil fuel cells. Bioresour. Technol. 2009;100: Wng Z, Lim B, Lu H, Fn J, Choi C. Cthodic reduction of Cu 2+ nd electric power genertion using microil fuel cell. Bul. Koren Chem. Soc. 2010;31: