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Transformation of dissolved organic matters in landfill leachate–bioelectrochemical system

Short Communication

Transformation of dissolved organic matters in land?ll leachate–bioelectrochemical

system

Guodong Zhang a ,b ,Yan Jiao c ,Duu-Jong Lee b ,d ,?

Institute of Resources and Environment Engineering,Shanxi University,Taiyuan 030006,China

Department of Chemical Engineering,National Taiwan University of Science and Technology,Taipei 10617,Taiwan c

Research Institute of Transition of Research-based Economics,Department of Environmental Economics,Shanxi University of Finance and Economics,Taiyuan 030006,China d

Department of Chemical Engineering,National Taiwan University,Taipei 106,Taiwan

h i g h l i g h t s

Bioelectrochemical system reactor

and anoxic/oxic reactor treated leachate.

BES removed 84–89%COD and 94–98%NH 4+-N,much higher than A/O reactor.

Dissolved organic matters in ef?uents from BES and A/O reactor were compared.

BES converted hydrophilic fraction of the fed DOM to CO 2and excess humin.

Electric ?elds at cathode assists ammonium removal by BES.

g r a p h i c a l a b s t r a c t

Leacha

a r t i c l e i n f o Article history:

Received 8May 2015

Received in revised form 22May 2015Accepted 23May 2015

Available online 28May 2015Keywords:

Land?ll leachate Microbial fuel cell Anoxic/oxic

Dissolved organic matter Fractionation

a b s t r a c t

A membraneless bioelectrochemical system (BES)reactor and an anoxic/oxic (A/O)reactor of identical con?gurations were applied to treat the land?ll leachate (20,100mg l à1chemical oxygen demand

(COD)and 1330mg l à1NH 4+-N)at 24-h hydraulic retention time and 3kg chemical oxygen demand m à3

d à1volum

e loading.The BES with maximum power density o

f 2.77±0.26W m à3and internal resistance of 47.5±1.4X removed 84–89%COD and 94–98%NH 4+-N,11%and 47%,respectively,higher than the A/O reactor.The dissolved organic matters (DOM)in ef?uents from the BES and the A/O reactor were for the ?rst time characterized and compared.The MFC preferentially degraded hydrophilic fraction (HPI)of the fed DOM and yielded excess humin with high aromaticity.The electric ?elds by bioelectrochemical reactions occurred at cathode stimulate the activities of COD degraders and nitri?ers in bio?lms to enhance ammonium removals by BES reactor.

1.Introduction

Land?ll leachate is heavily polluted wastewater with complex dissolved organic matter,inorganic macro-components,heavy metals and xenobiotic compounds (Kjeldsen et al.,2002).Microbial fuel cells (MFC)were devices to convert energy in organic or inorganic substances into electricity (Garner et al.,2012;Chou et al.,2014;Lee et al.,2014;Zhang et al.,2015a ).This device was applied for pollution removal and energy genera-tion from land?ll leachate (You et al.,2006;Zhang et al.,2008;Greenman et al.,2009;Gálvez et al.,2009;Puig et al.,2011;Tugtas et al.,2013;?zkaya et al.,2013;Ganesh and Jambeck,

?Corresponding author at:Department of Chemical Engineering,National Taiwan University,Taipei 106,Taiwan.Tel.:+886223625632;fax:+886223623040.

E-mail address:djlee@https://www.wendangku.net/doc/9212543195.html,.tw (D.-J.Lee).

2013;Vázquez-Larios et al.,2014;Damiano et al.,2014).These MFC studies noted28–74%removal of chemical oxygen demand (COD)and23–43%removal of NH4+in the leachate feed.To enhance cell performance,these mentioned studies commonly adopted noble metal catalysts to accelerate reaction rates on cathode and to separate the anode and cathode compartments by an ion exchange membrane to minimize backmixing of protons in the solution.However,application of noble catalyst or ion exchange membrane increases the installation costs of the leachate–MFC.

The tested leachate–MFC has low ammonium removal rates. Zhang et al.(2015b)proposed the use of a3.5-L membraneless MFC with biocathode,a bioelectrochemical system(BES),as a cost-effective device for leachate treatment.At3kg COD mà3dà1 loading and24-h hydraulic retention time(HRT),the tested mem-braneless BES could remove90%of fed COD and99%of NH4+in the leachate feed.Additionally,these authors aerated the solution around the cathode to produce anoxic/oxic local environment for removing nitrate to nitrogen gas.This newly proposed MFC presents an attractive alternative for land?ll leachate treatment, particularly on the almost complete removal of nitrogenous com-pounds that cannot be easily reached in conventional wastewater treatment process.The reasons for the supreme nitrogen removal capability by the tested BES remain unclear.

This study started up a membraneless BES as proposed by Zhang et al.(2015b)and an anoxic/oxic(A/O)reactor of identical geometry with the same operational protocol.The dissolved organic matters(DOM)in the ef?uents from both reactors were characterized for the?rst time based on their hydrophobicity and acidity.We noted a low Columbic ef?ciency of the tested BES,as commonly noted for other liter-scale BES being reported. The possible mechanisms corresponding to the noted high ammo-nium removal by the BES were discussed.

2.Methods

2.1.Reactor setup and test

The BES and the A/O reactor were of the same geometry as pro-posed by Zhang et al.(2015b).Brie?y,both the BES and A/O reactor were consisted of a cylindrical anode compartment of diameter of 10cm and height20cm,and a cathode compartment as the space outside the cylinder embraced by a cone of diameter14cm(bot-tom)and25cm(top)and of height18cm.Carbon?ber brushes embedded in graphite granules were?lled up the cathode and anode compartments for both reactors.The only difference between these two reactors is the former has an external circuit with a?xed resistance of100X while the latter was free from any external loading.

Land?ll leachates were collected from a land?ll site at Taiyuan, China,with the following mean characteristics(in mg là3):COD cr of20,100,BOD5of9035,total organic carbon(TOC)of7450, NH4+-N of1330,total nitrogen(TN)of1500,alkalinity of6720, and pH7.4.The leachate was fed to the inner cylindrical compart-ments at volume loading of3kg COD mà3dà1.All experiments were conducted at room temperatures.The cone compartment was intermittently aerated at500ml minà1in30min aera-tion+90min no-aeration cycles.

2.2.Extraction and fractionation of DOM

The collected samples(original leachate and the ef?uents from A/O reactor and from MFC)were?ltered by0.45l m cellulose nitrate membrane?lter.The?ltrate was diluted with30volumes of deionized water and then was acidi?ed to pH2using HCl.The DOM in?ltrates was fractionated using Amberlite XAD-8and XAD-4resins into?ve organic fractions:hydrophobic acid (HPO-A),hydrophobic neutral(HPO-N),transphilic acid(TPI-A), transphilic neutral(TPI-N),and hydrophilic fraction(HPI).Brie?y, 3000ml of acidi?ed?ltrate was passed through XAD-8and XAD-4resin columns at a?ow rate of10bed volumes per hour with the HPI was the organic matter in the XAD-4ef?uent.Each of the resin columns was eluted backward with0.1M NaOH at a ?ow rate of2bed volumes per hour,followed by2bed volumes of milli-Q water.The elute from XAD-8was the HPO-A,and that from XAD-4was TPI-A.The HPO-N and TPI-N were those being respectively adsorbed on XAD-8and XAD-4resins but were not eluted by NaOH.Detailed description of fractionation scheme is available in Wei et al.(2011).

2.3.Analytics and calculations

The potentials of the cathode and the anode were monitored with Ag/AgCl reference electrode(+0.197V vs.standard hydrogen electrode(SHE))(model RE-5B,BASi,Ningbo,China).The volumet-ric power density was normalized by the anode liquor volume.The polarization curves were obtained by measuring the stable voltage generated at various external resistances(maintained for30min at each resistance),from which the maximum power density(P max) was estimated(Logan et al.,2006).The internal resistance(R int) of cell was determined from the slope of polarization curves.

All DOM measurements were done in triplicate with the aver-age and standard deviation being reported.The dissolved organic carbon(DOC)in the?ltrate was analyzed using TOC-5000Total Organic Carbon Analyzer(Shimadzu,Kyoto,Japan).The ultraviolet absorbance of samples was measured at254nm with a Shimadzu UV-2550UV/VIS spectrophotometer(Shimadzu,Kyoto,Japan).The speci?c ultraviolet light absorbance(SUVA)was calculated as (UV-254/DOC)?100.The total COD(TCOD),total nitrogen(TN), NH4+-N,and alkalinity contents were analyzed according to the Standard Methods(APHA,1998).The apparent molecular weight distribution of DOM was characterized by high-performance size exclusion chromatography(HPSEC)with UV-detection at254nm. Weight-average molecular weight(M w)and number-average molecular weight(M n)were calculated from the HPSEC-UV results with molecular weight standards of polyethylene glycol(0.6kDa, 1kDa,6kDa,20kDa).Polydispersity(d)of molecular weights was calculated with the equation of d=M w/M n.

The fast Fourier infrared spectroscopy(FTIR)spectra(KBr,1%)of samples were adopted by Spectrum1B(Perkin Elmer,Waltham, MA,USA)between4000cmà1and400cmà1.The excitation–emis-sion matrix(EEM)was measured in a1-cm cuvette using a Jasco FP-6500spectro?uorometer(Tokyo,Japan)at24°C.The organic samples were diluted to1mg là1of DOC using0.01M KCl and acidi?ed to pH3with1M HCl.A xenon lamp was the excitation source,and the excitation and emission slits were set to a5nm band-pass.Each EEM plot was generated by scanning excitation wavelengths from220nm to400nm with5nm steps and emitting ?uorescence between280and480nm with1nm steps.

3.Results and discussion

3.1.Reactor performance

The tested membraneless BES yielded a power curve with P max=2.77±0.26W mà3at7.5A mà3(Supplementary materials). Correspondingly,the open circuit voltage(OCV)was noted high (743±14mV),correlating to the low R int obtained(47.5±1.4X). These data suggested that the present BES was well operated with the fed leachate.

G.Zhang et al./Bioresource Technology191(2015)350–354351

The COD and NH 4+removals were shown in Fig.1for both BES

and A/O reactors.During the testing period,the COD removals of BES ranged 84–89%,all higher than those for the A/O reactor (69–81%).The removals for NH 4+-N of BES ranged 94–98%,much higher than those for A/O reactor (42–57%).3.2.Leachate organics

The HPI,HPO-A and TPI-A fractions were the principal compo-nents in the raw land?ll leachate,accounting for 28.3%,28.2%and 20.4%of the total DOC,respectively (Fig.2).The remaining organic fractions were HPO-N (12.3%)and TPI-N (10.8%).The BES removed 83.4%of DOC in the fed leachate,including 95.6%of HPI,87.6%of TPI-A,79.7%of TPI-N,75.5%of HPO-A and 69.9of HPO-N.The A/O reactor removed 78.1%of the DOC,including 77.6%of HPI,70.3%of TPI-N,66.7%of HPO-A and 61%of HPO-N,

all less than those by BES.Restated,both BES and A/O reactors preferably degraded hydrophilic and transphilic fractions in land-?ll leachate,with the former being performing better than the latter.

The molecular weights of the ?ve organic fractions in raw lea-chate,in BES ef?uent and in A/O reactor ef?uent were listed (Table 1).The BES and A/O reactors largely reduced M w and M n of all organic fractions in the raw leachate,with the former yield-ing slightly lower molecular weights of all fractions than the latter.The d value (M w /M n )of fractions HPO-A,TPIA,HPO-N and TPI-N of raw leachate were all greater than 4.39.After treatments,besides HPI,the d values of all other fractions were reduced.This ?nding suggested that the BES and A/O reactors produce end products of low molecular weights.

The SUVA of raw leachates (Fig.3)followed (in lm à1mg à1):HPO-A (1.73±0.1)>HPO-N (0.97±0.08)>TPI-N (0.82±0.09)>TPI-A

33%

16%

17%11%

23%

A/O Effluent

HPO-A

TPI-A

HPO-N TPI-N

HPI

28%

21%

12%

11%

28%Leachate

42%

15%

22%

13%8%

BES Effluent

2.Fractional DOC distributions of the raw leachate,A/O ef?uent and BES ef?uent.DOC concentration (A)and ratios 352G.Zhang et al./Bioresource Technology 191(2015)350–354

(0.42±0.04)>HPI(0.31±0.03).The aromatic macromolecules were enriched in HPO-A,HPO-N and TPI-N fractions.The SUVA for BES ef?uents were HPO-A(2.95±0.08)>TPI-A(2.37±0.16)>TPI-N (1.41±0.14),and those for A/O reactor ef?uents were HPO-A (1.84±0.14)>TPI-A(1.45±0.07)>TPI-N(1.12±0.11).The BES removed more non-aromatic compounds than A/O reactor from land-?ll leachate.

The FT-IR analysis(Supplementary materials)showed that all four organic fractions revealed signals between3300cmà1and 3670cmà1,attributing to stretch for hydroxyl groups.The absorp-tion intensities in the A/O ef?uents were stronger than in the BES ef?uent,both were weaker than the raw leachate.The BES removed most2950cmà1band(aliphatic C A H)in HPO-A and TPI-N fractions,1600cmà1peak(C@C bond)in HPO-A and HPI-A fractions,and1720cmà1(C@O bond),1390–1420cmà1(O A H bond)and1250–1050cmà1(hydrocarbon)in leachate.The A/O reactor also removed these peaks,but also yielded new peaks: 1190cmà1(C A O stretching),1540cmà1(N A H bending), 1640cmà1(C@O stretching of amide),810cmà1(C A H vibration or N A H out of plane).

All?ve organic fractions of the raw land?ll leachate had notice-able EEM peaks in Regions II,III and IV in Chen et al.(2003) (Supplementary materials),referring to the redundancy of aro-matic proteins,fulvic acid-like components and soluble microbial byproduct-like(SMP-like)materials,respectively.The aromatic proteins and SMP-like substances predominated in the four frac-tions of the raw leachate except for the HPO-A,with the intensity following TPI-N>HPO-N>TPI-A>HPI.The A/O ef?uent had simi-lar EEM pro?les as those for raw leachate;while the BES ef?uent had a very different characteristic.All fractional EEM of the A/O ef?uents showed high?uorescent intensity in Regions II and IV, indicating that the A/O reactions were enriched with aromatic proteins and SMP-like substances.Conversely,the BES ef?uent was rich with fulvic acid-like and humic acid-like substances in order of HPO-A>TPI-A>HPI.The way MFC transforms the organic matters in leachate during treatment corresponds to literature results handling various inf?uents.

3.3.Role of bioelectrochemical reactions on cell performance

The BES and A/O reactors favorably degraded hydrophilic and transphilic fractions in land?ll leachate to form end products of high aromaticity.In particular,the BES completely removed easily degradable organic compounds to excess fulvic acid-like and humic acid-like substances.The ef?uent from A/O reactor,con-versely,contained large amounts of intermediates as evidenced by FTIR spectra.Restated,the bioelectrochemical reactions in BES accelerated COD degradation by enhancing conversion of hydro-philic and transphilic organic substances to CO2or humins,leading to the noted high COD removal(84–89%).On the other hand,since the total electron quantity during the30-d operation,estimated based on the current–time data,was0.75mol eà.Meanwhile,the COD removed by BES was315g and the ammonium removal(to nitrate)was21g,accounting for50.7mol of electron transferred. Hence,the Columbic ef?ciency of the present leachate–BES was only 1.47%.This very low ef?ciency(but common in reported liter-scale BES)suggests that direct bioelectrochemical reaction at cathode should not be responsible for the noted enhanced COD removal,nor for the supreme removal ef?ciency for nitroge-nous compounds by BES.

Since direct bioelectrochemical reactions were not responsible to the noted cell performance,indirect mechanisms are looking for.The present study supports a proposal as follows.The electric ?eld around the cathodic bio?lm of BES stimulates the activity of the incorporated functional microorganisms,leading to high ef?-ciencies of COD degradation and nitri?cation.The removal of high molecular weight and low aromaticity substances releases much inhibition on nitri?ers in bio?lms,yielding high ammonium removal.Suf?cient nitrate supply led to high denitri?cation rates in anodic compartment under anoxic environment.

4.Conclusions

At P max of2.77±0.26W mà3at a current density of7.5A mà3, the bio?lm of tested BES removed86.3±1.3%COD and 96.7±0.9%NH4+-N at3kg COD mà3dà1volume loading,much higher than the control,an A/O reactor of identical geometry.The organic compounds preferably removed by BES followed95.6% HPI,87.6%TPI-A,79.7%TPI-N,75.5%HPO-A and69.9%HPO-N, being of high molecular weights and low SUVA.The bioelectro-chemical reactions did not directly degrade the organic substances; indirectly,the electric?eld thus generated at cathodic bio?lm stimulates the microbial activity for enhanced COD removal and nitri?cation.

Acknowledgements

The authors gratefully acknowledge funding from project 51408350by National Nature Science Foundation of China,and

Table1

Mean molecular weights and polydispersity of DOM fractions in the raw leachate,A/O

ef?uent and BES ef?uent.

Fraction M w(Da)M n(Da)Polydispersity

Raw leachate

HPO-A97,80015,870 6.16

TPI-A4920980 5.02

HPO-N4810930 5.17

TPI-N3690840 4.39

HPI20,62016,210 1.27

A/O ef?uent

HPO-A17101120 1.53

TPI-A14801150 1.29

HPO-N950620 1.53

TPI-N870610 1.41

HPI14401060 1.36

BES ef?uent

HPO-A15501090 1.42

TPI-A14901250 1.19

HPO-N840550 1.53

TPI-N750570 1.32

HPI1020820 1.24

G.Zhang et al./Bioresource Technology191(2015)350–354353

project2013125supported by Scienti?c and Technological Innovation Programs of Higher Education Institutions in Shanxi. Appendix A.Supplementary data

Supplementary data associated with this article can be found,in the online version,at https://www.wendangku.net/doc/9212543195.html,/10.1016/j.biortech.2015.05. 082.

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