Reducing organic loads in wastewater effluents from paper recycling plants using microbial fuel cells

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1 Environmentl Technology Vol. 3, No. 5, 14 April 29, Reducing orgnic lods in wstewter effluents from pper recycling plnts using microil fuel cells Liping Hung,, Shon Cheng, Frzneh Rezei c nd Bruce E. Logn * School of Environmentl nd Biologicl Science nd Technology, Dlin University of Technology, Dlin, 11624, Chin; Deprtment of Civil nd Environmentl Engineering, The Pennsylvni Stte University, University Prk, PA, 1682, USA; c Deprtment of Agriculturl nd Biologicl Engineering, The Pennsylvni Stte University, University Prk, PA, 1682, USA Tylor nd Frncis 1.18/ (Received 13 Novemer 28; Accepted 3 Jnury 29) Downloded By: [Logn, Bruce E.] At: 16:1 6 April 29 Mny industries re chrged fees sed on the orgnic lods in effluents. Therefore, it cn e dvntgeous to reduce the wstewter strength prior to dischrge. We investigted the use of microil fuel cells (MFCs) to reduce the chemicl oxygen demnd (COD) of pper-plnt wstewter while t the sme time producing electricity in continuous flow system. At hydrulic retention time (HRT) of six hours, COD removl using n unmended wstewter (56 mg/l COD) (orgnic loding rte, OLR = 2. kg COD/(m 3 d)) ws 26±2%, with power density of 5.9±.2 W/m 3 (21±7 mw/m 2 ). This mount of power ws similr to the mximum power density (5.2±.4 W/m 3 ) produced in fed-tch tests using slightly lower strength wstewter in the sme device (45 mg/l COD). Incresing the HRT to 25 h (OLR =.5 kg COD/(m 3 d)) incresed COD removl (41±2%) ut sustntilly decresed power (2.8±.3 W/m 3 ). While wstewter strength ffected removl rtes, the solution conductivity (.8 ms/cm) ws primrily fctor in low power production. These results demonstrte tht MFCs cn e used to reduce orgnic lods in effluents t reltively short HRTs, while t the sme time generting power. Keywords: microil fuel cell; pper recycling wstewter; COD removl; solution conductivity; hydrulic retention time; influent wstewter strength Introduction Microil fuel cells (MFCs) generte electricity directly from vrious iodegrdle sustrtes through microil relese of electrons to n electrode. Microil fuel cells cn e used to recover energy from wstewter while eliminting the need for wstewter ertion nd reducing sludge production [1,2]. Severl types of wstewter hve een exmined including municipl, food processing, rewery, niml nd pper recycling wstewters [3 9]. In most of these studies, fed-tch tests hve een conducted lthough in some cses continuous flow tests hve een conducted primrily using domestic wstewters [3,4,7]. In mny wstewter tretment studies, the gol of tretment is to reduce chemicl oxygen demnd (COD) to levels sufficient to meet dischrge limittions. In other cses, however, extensive tretment is not needed s the wstewter is often sent to municipl tretment plnts for further tretment nd nutrient removl. These industries py fees sed on the orgnic lods in the dischrged wstewter. Therefore, reducing COD concentrtions cn sve the industries money s well s reduce the lods on the locl tretment plnt. This could help to improve the ility of the municipl plnt to ccept other wstewters or postpone municipl plnt expnsion llowing it to meet incresed lods from other sources. Moreover, some industries re limited in the mount of orgnics tht they cn dischrge to tretment plnt, which cn limit further economic growth of these industries. We were interested in exmining to wht extent MFCs could e used to rpidly decrese COD concentrtions in industril wstewters. A locl pper recycling plnt hd found tht they were unle to increse plnt production due to COD limits on their dischrge permit. In ddition, their existing fees for wstewter dischrge were expensive. Conventionl neroic digester tretment ws not fesile due to low concentrtion of orgnic mtter in the wstewter [9,1]. Aeroic tretment required high energy input nd therefore ws not desirle. In previous tests using this wstewter, we found tht y using single-chmer MFC we could generte mximum of.2 W/m 3 (144 mw/m 2 ) t the eginning of fed-tch cycle with this wstewter (unmended) contining 146 mg/l of totl chemicl oxygen demnd (TCOD) [9]. This level *Corresponding uthor. Emil: logn@psu.edu ISSN print/issn X online 29 Tylor & Frncis DOI: 1.18/

2 5 L. Hung et l. Downloded By: [Logn, Bruce E.] At: 16:1 6 April 29 of power production ws low, nd power vried over the course of fed-tch cycle. In ddition, the fedtch cycle lsted 35 hours, with finl COD removl of only 29%. This length of time ws too long to mke MFC tretment fesile under these conditions. Therefore, we resoned tht if the time could e shortened, then tretment might e economicl even if COD removl ws incomplete. The gol of this current project ws to exmine COD removl under continuous-flow conditions in order to evlute the effect of hydrulic retention time (HRT) on COD removl nd electricity genertion. We used n improved type of MFC, compred with previous tests, in order to increse power production nd decrese the time needed for tretment. Mterils nd methods MFC rector construction nd opertion The MFCs were constructed sed on n efficient ircthode design, with liquid chmer 4 cm long nd 3 cm in dimeter [11]. The node ws n mmonigs-treted cron rush (totl surfce re of.224 m 2 or 18, 2 m 2 /m 3 of rush volume, PANEX33 16K, ZOLTEK) [12] nd the ir cthode contined.5 mg/ cm 2 Pt (wter side) nd four diffusion lyers (ir-side) on 3 wt% wet-proofed cron cloth (type B-1B, E- TEK) [13]. The distnce from the edge of the rush to the cthode ws 1.5 cm. In the first set of experiments, the rector ws inoculted using only the cteri present in the pper recycling wstewter (PRW) collected from the primry clrifier of the wstewter tretment plnt, nd it ws operted in tch mode. The rector solution ws replced with fresh PRW fter power production dropped to elow 1% of the mximum power output. After four trnsfers, power output ws repetle, indicting the stle performnce of the iofilm on the node. Pper recycling wstewter ws continuously pumped into the rector nd used s the fuel without ny modifictions, except in diluted wstewter tests s noted. All mesurements were tken fter the rector hd een operted for t lest 4 5 HRTs, with stle power output. All rectors were run in duplicte or triplicte, nd mesurements were tken over two or three consecutive retention times. Duplicte rectors were operted in open circuit mode (disconnected electrode) s control for COD removl in the sence of power genertion. A second control ws set up to ccount for COD or BOD (iochemicl oxygen demnd) losses unrelted to the plcement of the smple in the MFC where oxygen cn lek into the rector through the cthode (ottle control). All experiments were conducted t room temperture (22 26 C). Anlysis The voltge (V) cross n externl resistor (1 Ω) in the MFC circuit ws monitored t 2 min intervls using multimeter (Keithley Instruments, Clevelnd, OH) connected to personl computer. Current (I), power (P = IV), nd Coulomic efficiencies (CEs) were clculted s previously descried [14], with the power density normlized y the projected surfce re of the cthode (7 cm 2 ) nd volumetric power density normlized y the volume of the liquid medium. Internl resistnce ws clculted s the slope of the voltge current plot otined y vrying externl resistnce [15]. Smples were collected from the influents nd the effluents of the rectors for COD nlysis. For BOD 5 determintion, these smples needed to e diluted 1 2 times efore nlysis. Chemicl oxygen demnd nd BOD 5 were mesured in duplicte using Stndrd Methods [16]. Wstewter Pper recycling wstewter (1 L, ech smple) ws collected from the primry clrifier of the wstewter tretment plnt t the Americn Egle Pper Compny, Tyrone, Pennsylvni nd stored t 4 C until used. In previous tch tests, we found performnce ws improved y treting only the wstewter superntnt. Therefore, smples were settled for 48 h, nd only the superntnt (top 5 L) ws used in tests. The chrcteristics of the wstewter re shown in Tle 1. In some tests, the wstewter ws diluted using ultrpure wter (Milli-Q system: Millipore Corp., New Bedford, MA) with the solution conductivity mintined y ddition of 1. M NCl. In ddition, in some tests phosphte uffer solution (PBS) ws dded directly to the wstewter t concentrtion of 5 mm (NH 2 PO 4 H 2 O: g/l, nd N 2 HPO 4 : g/l) or higher s noted. Unless stted, ph in the MFC chmer ws not djusted y PBS. Results The MFCs were initilly cclimted in fed-tch mode, where it ws found tht fter three cycles (>4 h), the Tle 1. Prmeters Chrcteristic prmeters of the PRW. Vlue ph Conductivity (ms/cm).78.8 TCOD (g/l) SCOD (g/l) BOD (g/l).15.2 Ammoni nitrogen (g/l).17.2 Reducing sugrs (g/l).12.17

3 Environmentl Technology 51 Downloded By: [Logn, Bruce E.] At: 16:1 6 April 29 voltge reched stle vlue of.36±.2 V (1 Ω) fter replcing the wstewter. The mximum power density using this MFC in fed-tch mode ws 5.2±.4 W/m 3 (185±9 mw/m 2 ) for wstewter with n initil TCOD of 45±8 mg/l. This power production ws 26 times (.2 W/m 3, 144 mw/m 2 ) tht previously otined using this source of wstewter in fed-tch tests with different type of MFC [9]. The rectors were then switched to continuous flow opertion using newly collected tch of PRW hving n influent strength of 56±1 mg/l in order to determine the effect of retention time on tretment. At n HRT of 6 h, the voltge ws stle t.38 V (externl resistnce 1 Ω), producing 5.9 W/m 3 (Figure 1). Bsed on polriztion dt, this ws lso the mximum power density chievle for this system (5.9±.2 W/m 3, 21±7 mw/m 2 ), t current density of 15 A/m 3 (R ex = 1 Ω) (Figure 1). The open circuit voltge (OCV) of the cell ws.72 V under continuous flow conditions. The polriztion dt were liner over wide rnge of Voltge (V) Time (h) current densities ( A/m 3, R 2 =.998) indicting power production ws limited y high ohmic resistnce ( 1 Ω), likely due to the low solution conductivity (Figure 1). Figure 1. () Voltge produced during continuous flow opertion (R ex = 1 Ω). () Polriztion nd power density curves otined during stedy stte opertion. (HRT = 6 h; influent = 56 ±1 mg/l). Power production, CE nd COD removl were mesured s function of wstewter strength t n HRT of 6 h due to the fct tht wstewter concentrtions cn vry during the dy t this tretment plnt (Figure 2). Power density ws function of wstewter strength, incresing from 1.6±.2 W/m 3 to 5.9±.2 W/m 3 s function of the influent CODs tht vried from 136 mg/l to 56 mg/l. The CEs decresed slightly over this rnge from 3±3% to 21±2% (Figure 2). The highest initil COD (56 mg/l) resulted in COD removl of 26±2% in these tests, compred with 38±3% t the lowest initil COD (136 mg/l). The COD removls occurred s result of processes other thn electricity genertion over this time period in the MFC. When the rector ws operted in open-circuit mode, COD removls decresed from 11±2% to 15±2% (Figure 2). Figure 2. Power genertion s function of influent COD concentrtion fixed externl resistnce (1 Ω, HRT = 6 h). Orgnic mtter removl in terms of BOD ws nerly constnt t 56±2% for the sme rnge of initil CODs. Some BOD removl my hve occurred in the ottle control (2 1% vrition in BOD), proly s result Power density (W/m 3 ) power density CE CE (%) Voltge (V) voltge power density Power density (W/m 3 ) COD removl (%) MFC electrode control Current density (A/m 3 ) Figure 1. () Voltge produced during continuous flow opertion (R ex = 1 Ω). () Polriztion nd power density curves otined during stedy stte opertion. (HRT = 6 h; influent COD = 56±1 mg/l) Influent COD (mg/l) Figure 2. Power genertion, CE () nd COD removl () s function of influent COD concentrtion t fixed externl resistnce (1 Ω, HRT = 6 h).

4 52 L. Hung et l. Downloded By: [Logn, Bruce E.] At: 16:1 6 April 29 of methnogenesis. The rtio of BOD to COD rnged from.28 to.3 for influent CODs of mg/l, indicting the low iodegrdility of the mteril in the PRW. This vlue decresed further to.18.2 for the effluent, showing the effectiveness of the tretment using the MFC. This shows tht very little of the orgnic mtter in this wstewter cn e iologiclly degrded, nd tht COD removls were typiclly lower thn those for BOD removl s result of lrge frction of non-iodegrdle mtter [17,18]. Effect of HRT on power genertion COD removl incresed from 15±2% t n HRT of 2 h, t n orgnic loding rte (OLR) of 6. kg COD/(m 3 d), to mximum of 41±2% t n HRT of 25 h (OLR =.5 kg COD/(m 3 d)) (Figure 3). These removls were lrger y fctor of compred with COD removls in the open-circuit control, which rnged from 5±1% to 23±2% over the sme rnge of HRTs (Figure 3). Chnging the HRT from 2 h to 15 h did not sustntilly ffect power densities. Power decresed slightly from 6.2±.3 W/m 3 to 5.5±.3 W/m 3 for HRTs of 2 15 h. However, power decresed sustntilly to 2.8±.3 W/m 3 when the HRT ws incresed to 25 h (Figure 3). This shows tht lower COD removl (%) Power density (W/m 3 ) MFC control HRT (h) power density CE CE (%) Figure 3. COD removl (), power density nd CE () s function of HRT (initil TCOD 498 mg/l, 1 Ω). power production t longer HRTs ws due to the low COD concentrtion in the rector. Figure 3. COD removl (), power density nd () s function of HRT (initil TCOD 498 mg/l, 1 Ω). The CEs t these different HRTs rnged from 13±.3% to 39±2%, corresponding to COD removls of 15±2% to 41±2%. The totl per cent of electrons extrcted from orgnic mtter, defined s E T, is equl to the CE multiplied y COD removl [19]. Bsed on clculted vlues of E T, the totl per cent of electrons extrcted ws 2 16% of the totl COD removed. This indictes tht the remining 13 25% of COD removed ws due to neroic nd/or eroic respirtion, iomss growth nd/or other unidentified processes (Figure 3). Effect of solution conductivity Solution conductivity hs een identified s min fctor limiting power genertion, ut it lso ffects COD removl [8,9,13,15,19]. Incresing the conductivity will produce higher current densities, nd therefore presumly greter COD removls. When PBS ws dded to the PRW to increse the solution conductivity, power genertion incresed from 5.6±.2 W/m 3 (2±6 mw/m 2, solution conductivity.8 ms/cm) to s much s 16±1 W/m 3 (562±2 mw/m 2, 1 mm PBS, 1.2 ms/cm) (Figure 4). This increse in power with solution conductivity clerly shows tht power production ws limited y ohmic resistnce. As expected, the higher solution conductivity reduced the internl resistnce. Bsed on the liner portion of the polriztion curve (Figure 4), the internl resistnces decresed from 82 Ω for the unmended PRW, to 28 Ω for 1 mm PBS. The COD removls were incresed from 28±2% in unmended PRW to 37±3% with 1 mm PBS (Figure 4c). The CEs incresed from 22±2% to 26±2% in 1 mm PBS (Figure 4c). Figure 4. Volumetric power density (), voltge s function of current (), nd COD removl nd CE (c) t different PBS concentrtions in C-MFC (influent 449 mg/l). Discussion It ws demonstrted here tht the COD in wstewter from pper recycling plnt could e reduced y 26±2% using n HRT of only 6 h, while producing 5.9±.2 W/m 3. Under these conditions, the mount of power ws reltively unffected y COD concentrtion or y the opertion of the rector under continuous flow conditions. In the initil fed-tch tests, the mximum power produced (5.2±.4 W/m 3 ) ws pproximtely the sme mount of power produced under continuous flow conditions. Although the CE otined here ws low (22±2%, influent COD of 449 mg/l), it ws higher thn hs een chieved with some wstewters in continuous flow tests, such s 3 12% using domestic wstewter [3]. Incresing the HRT incresed COD removl somewht, ut t very long HRT (25 h). This resulted in sustntil decrese in power production. The effect of the long HRT is to reduce the verge COD concentr-

5 Environmentl Technology 53 Downloded By: [Logn, Bruce E.] At: 16:1 6 April 29 tion in the MFC, thus lowering power production s result of the decrese in concentrtion of sustrte. This effect of sustrte concentrtion on power production hs een shown in MFCs to occur t low sustrte concentrtions, in mnner consistent with Monod Power density (W m Ð3 ) Voltge (V) COD removl (%) Current density(am Ð3 ) no PBS 5 mm PBS 1 mm PBS Current (ma) no PBS 5 mm PBS 1 mm PBS PBS concentrtion (mm) COD removl Figure 4. Volumetric power density (), voltge s function of current (), nd COD removl nd CE (c) t different PBS concentrtions in the MFC (influent 449 mg/l). CE c kinetics [2]. Thus, gol of incresed power densities must e lnced with COD removl efficiencies when designing systems for prcticl pplictions. The percentge of the COD removl tht went into iomss growth (or other unidentified processes) in the present study ws lower thn found in other studies with more esily degrded or fermented sustrtes. We found tht only 13 25% of the totl COD removed went to iomss or other processes, compred with 4 89% in tch-fed two-chmer MFC using glucose nd cette s sustrtes [21,22]. Solution conductivity nd the uffer cpcity of the wstewter cn limit mximum power densities chieved with MFCs [8,9,13,15,19]. Conductivity limited power production s shown y the fct tht power could e incresed to 16±1 W/m 3 y dding phosphte uffer. Oviously, it is not prcticl or desirle to increse wstewter conductivity using slts or phosphte solutions (which dds nutrients). Our use of the uffer ws only done to emphsize the impct of low solution conductivity on rector performnce. Solution conductivity is not routinely reported for wstewters, ut domestic wstewters in Stte College PA vry from.8 ms/cm to 2 ms/cm. This rnge compres well to wstewters in Austrli, which vry from 1.4 ms/cm to 1.8 ms/cm [23,24]. These vlues re slightly lower thn rewery wstewter used in previous MFC tests, which hd solution conductivity of 3.2 ms/cm [8]. Wstewters with higher solution conductivities will help lower internl resistnce nd increse power genertion. A uffer is lso importnt for reducing ph grdients t the electrodes [25]. While our results show tht continuous power production is fesile for this industril wstewter, much dditionl work will e needed to otin n MFC tht is economiclly vile for COD removl for this wstewter. In ddition, pilot-scle tests re needed to etter evlute process design fctors, such s sludge production, nd mterils tht cn e used to construct MFCs for lrger systems. We used rush nodes here, which we expect re esily scled up for use in lrger systems. However, we still need to otin dt using more sclle cthode designs, such s tuulr cthodes, nd cthodes tht do not use precious metls, such s Co-tetr-methyl phenylporphyrin (CoTMPP) [26,27]. Additionl reserch nd further investigtion of these mterils should led to more efficient nd economicl designs for rectors tht cn e prcticlly pplied for PRW tretment nd electricity genertion. Acknowledgements The uthors thnk Jmes R. Zuhlke, Dvid Jones, nd Elodie Llurette for help with wstewter smpling nd nlysis.

6 54 L. Hung et l. Downloded By: [Logn, Bruce E.] At: 16:1 6 April 29 This work ws supported through n I-99 Micro Industry Reserch Grnt y the Altoon Blir County Development Corportion nd the Ben Frnklin Technology Prtners, the Americn Egle Pper Mills, NREL contrct RFH , nd the Pul L. Bush wrd dministered y the Wter Environment Reserch Foundtion. References [1] B.E. Logn nd J. Regn, Microil fuel cells: Chllenges nd pplictions, Environ. Sci. Technol. 4 (26), pp [2] L. Hung, R. Zeng, nd I. Angelidki, Electricity production from xylose using meditor-less microil fuel cell, Bioresour. Technol. 99 (28), pp [3] H. Liu, R. Rmnrynn, nd B.E. Logn, Production of electricity during wstewter tretment using single chmer microil fuel cell, Environ. Sci. Technol. 38 (24), pp [4] B. Min nd B.E. Logn, Continuous electricity genertion from domestic wstewter nd orgnic sustrtes in flt plte microil fuel cell, Environ. Sci. Technol. 38 (24), pp [5] B. Min, J. Kim, S. Oh, J. Regn, nd B.E. Logn, Electricity genertion from swine wstewter using microil fuel cells, Wter Res. 39 (25), pp [6] S. Oh nd B.E. Logn, Hydrogen nd electricity production from food processing wstewter using fermenttion nd microil fuel cell technologies, Wter Res. 39 (25), pp [7] S. You, Q. Zho, J. Zhng, nd J. Zhng, Tretment of domestic wstewter with simultneous electricity genertion in microil fuel cell under continuous opertion, Chem. Biochem. Eng. Q. 2 (27), pp [8] Y. Feng, X. Wng, B.E. Logn, nd H. Lee, Brewery wstewter tretment using ir-cthode microil fuel cells, Appl. Microiol. Biotechnol. 78 (28), pp [9] L. Hung nd B.E. Logn, Electricity genertion nd tretment of pper recycling wstewter using microil fuel cell, Appl. Microiol. Biotechnol. 8 (28), pp [1] P. Lens, H. Pol, P. Wilderer, nd T. Asno, Wter recycling nd resource recovery in industry: Anlysis, technologies nd implementtion, Interntionl Wter Assocition, London, 22. [11] B.E. Logn, S. Cheng, V. Wtson, nd G. Estdt, Grphite fier rush nodes for incresed power production in ir-cthode microil fuel cells, Environ. Sci. Technol. 41 (27), pp [12] S. Cheng nd B.E. Logn, Ammoni tretment of cron cloth nodes to enhnce power genertion of microil fuel cells, Electrochem. Commun. 9 (27), pp [13] S. Cheng, H. Liu, nd B.E. Logn, Incresed performnce of single-chmer microil fuel cells using n improved cthode structure, Electrochem. Commun. 8 (26), pp [14] L. Hung nd I. Angelidki, Effect of humic cids on electricity genertion integrted with xylose degrdtion in microil fuel cells, Biotechnol. Bioeng. 1 (28), pp [15] H. Liu, S. Cheng, L. Hung, nd B.E. Logn, Scle-up of memrne-free single-chmer microil fuel cells, J. Power Sources 179 (28), pp [16] APHA, AWWA nd WEF, Stndrd Methods for the Exmintion of Wter nd Wstewter, 2th edn., Americn Pulic Helth Assocition, Wshington, D.C., [17] H. Lee, T. Pert, nd J. Crron, Gs chromtogrphic nd mss spectrometric determintion of some resin nd ftty cids in pulp mill effluents s their pentfluoroenzyl ester derivtives, J. Chromtogr. 498 (199), pp [18] A. Rigol, A. Ltorre, S. Lcorte, nd D. Brcelo, Determintion of toxic compounds in pper-recycling process wters y gs chromtogrphy mss spectrometry nd liquid chromtogrphy mss spectrometry, J. Chromtogr. 963 (22), pp [19] L. Hung nd B.E. Logn, Electricity production from xylose in fed-tch nd continuous-flow microil fuel cells, Appl. Microiol. Biotechnol. 8 (28), pp [2] B.E. Logn, Microil Fuel Cells, Wiley-Interscience, Hooken, N.J., 27. [21] S. Fregui, K. Rey, Z. Yun, nd J. Keller, Electron nd cron lnces in microil fuel cells revel temporry cteril storge ehvior during electricity genertion, Environ. Sci. Technol. 41 (27), pp [22] J. Kim, S. Cheng, S. Oh, nd B.E. Logn, Power genertion using different ction, nion, nd ultrfiltrtion memrnes in microil fuel cells, Environ. Sci. Technol. 41 (27), pp [23] T. Mrshll nd L. Don, Delivery nd performnce of the luggge point wstewter tretment plnt wter reclmtion project, Contrct to John Hollnd Pty Ltd., Brisne, Queenslnd, Austrli. (21). [24] B. Tylor, T. Grdner, nd S. Kenwy, Southest Queenslnd recycled wter spects nd soil impcts, Queenslnd AWA (Austrlin Wter Assocition) Regionl Conference, Brisne, Queenslnd, Austrli, 27. [25] Y. Fn, H. Hu, nd H. Liu, Sustinle power genertion in microil fuel cells using icronte uffer nd proton trnsfer mechnisms, Environ. Sci. Technol. 41 (27), pp [26] Y. Zuo, S. Cheng, D. Cll, nd B.E. Logn, Tuulr memrne cthodes for sclle power genertion in microil fuel cells, Environ. Sci. Technol. 41 (27), pp [27] Y. Zuo, S. Cheng, nd B.E. Logn, Ion exchnge memrne cthodes for sclle microil fuel cells, Environ. Sci. Technol. 42 (28), pp