Bioresource Technology 191 (2015) 350–354
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Transformation of dissolved organic matters in landfill leachate–bioelectrochemical system Guodong Zhang a,b, Yan Jiao c, Duu-Jong Lee b,d,⇑ a
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 b
g r a p h i c a l a b s t r a c t
Bioelectrochemical system reactor
a r t i c l e
i n f o
Article history: Received 8 May 2015 Received in revised form 22 May 2015 Accepted 23 May 2015 Available online 28 May 2015 Keywords: Landfill leachate Microbial fuel cell Anoxic/oxic Dissolved organic matter Fractionation
800 Voltage
210
3.0
600
2.5
500
2.0
400
1.5
300 1.0 200 0.5
100
Leacha
180 150 90 60 30
0.0
0 0
2
4
6
8
10
Current density (A m-3)
12
14
0
HPO-A
TPI-A
HPO-N
TPI-N
HPI
a b s t r a c t A membraneless bioelectrochemical system (BES) reactor and an anoxic/oxic (A/O) reactor of identical configurations were applied to treat the landfill leachate (20,100 mg l 1 chemical oxygen demand (COD) and 1330 mg l 1 NH+4-N) at 24-h hydraulic retention time and 3 kg chemical oxygen demand m 3 d 1 volume loading. The BES with maximum power density of 2.77 ± 0.26 W m 3 and internal resistance of 47.5 ± 1.4 X 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 effluents from the BES and the A/O reactor were for the first time characterized and compared. The MFC preferentially degraded hydrophilic fraction (HPI) of the fed DOM and yielded excess humin with high aromaticity. The electric fields by bioelectrochemical reactions occurred at cathode stimulate the activities of COD degraders and nitrifiers in biofilms to enhance ammonium removals by BES reactor. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Landfill leachate is heavily polluted wastewater with complex dissolved organic matter, inorganic macro-components, heavy ⇑ Corresponding author at: Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan. Tel.: +886 2 23625632; fax: +886 2 23623040. E-mail address: [email protected] (D.-J. Lee). http://dx.doi.org/10.1016/j.biortech.2015.05.082 0960-8524/Ó 2015 Elsevier Ltd. All rights reserved.
Power density
700
Voltage (mV)
and anoxic/oxic reactor treated leachate. BES removed 84–89% COD and 94– 98% NH4+-N, much higher than A/O reactor. Dissolved organic matters in effluents from BES and A/O reactor were compared. BES converted hydrophilic fraction of the fed DOM to CO2 and excess humin. Electric fields at cathode assists ammonium removal by BES.
Power density (W m-3)
h i g h l i g h t s
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 generation from landfill 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; Özkaya et al., 2013; Ganesh and Jambeck,
G. Zhang et al. / Bioresource Technology 191 (2015) 350–354
2013; Vázquez-Larios et al., 2014; Damiano et al., 2014). These MFC studies noted 28–74% removal of chemical oxygen demand (COD) and 23–43% removal of NH+4 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 a 3.5-L membraneless MFC with biocathode, a bioelectrochemical system (BES), as a cost-effective device for leachate treatment. At 3 kg COD m 3 d 1 loading and 24-h hydraulic retention time (HRT), the tested membraneless BES could remove 90% of fed COD and 99% of NH+4 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 landfill leachate treatment, particularly on the almost complete removal of nitrogenous compounds 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 effluents from both reactors were characterized for the first time based on their hydrophobicity and acidity. We noted a low Columbic efficiency of the tested BES, as commonly noted for other liter-scale BES being reported. The possible mechanisms corresponding to the noted high ammonium 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 proposed by Zhang et al. (2015b). Briefly, both the BES and A/O reactor were consisted of a cylindrical anode compartment of diameter of 10 cm and height 20 cm, and a cathode compartment as the space outside the cylinder embraced by a cone of diameter 14 cm (bottom) and 25 cm (top) and of height 18 cm. Carbon fiber brushes embedded in graphite granules were filled 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 fixed resistance of 100 X while the latter was free from any external loading. Landfill leachates were collected from a landfill site at Taiyuan, China, with the following mean characteristics (in mg l 3): CODcr of 20,100, BOD5 of 9035, total organic carbon (TOC) of 7450, NH+4-N of 1330, total nitrogen (TN) of 1500, alkalinity of 6720, and pH 7.4. The leachate was fed to the inner cylindrical compartments at volume loading of 3 kg COD m 3 d 1. All experiments were conducted at room temperatures. The cone compartment was intermittently aerated at 500 ml min 1 in 30 min aeration + 90 min no-aeration cycles.
351
XAD-4 resins into five organic fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N), and hydrophilic fraction (HPI). Briefly, 3000 ml of acidified filtrate was passed through XAD-8 and XAD-4 resin columns at a flow rate of 10 bed volumes per hour with the HPI was the organic matter in the XAD-4 effluent. Each of the resin columns was eluted backward with 0.1 M NaOH at a flow rate of 2 bed volumes per hour, followed by 2 bed volumes of milli-Q water. The elute from XAD-8 was the HPO-A, and that from XAD-4 was TPI-A. The HPO-N and TPI-N were those being respectively adsorbed on XAD-8 and XAD-4 resins 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 (+0.197 V vs. standard hydrogen electrode (SHE)) (model RE-5B, BASi, Ningbo, China). The volumetric 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 for 30 min at each resistance), from which the maximum power density (Pmax) was estimated (Logan et al., 2006). The internal resistance (Rint) of cell was determined from the slope of polarization curves. All DOM measurements were done in triplicate with the average and standard deviation being reported. The dissolved organic carbon (DOC) in the filtrate was analyzed using TOC-5000 Total Organic Carbon Analyzer (Shimadzu, Kyoto, Japan). The ultraviolet absorbance of samples was measured at 254 nm with a Shimadzu UV-2550 UV/VIS spectrophotometer (Shimadzu, Kyoto, Japan). The specific ultraviolet light absorbance (SUVA) was calculated as (UV-254/DOC) 100. The total COD (TCOD), total nitrogen (TN), NH+4-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 at 254 nm. Weight-average molecular weight (Mw) and number-average molecular weight (Mn) were calculated from the HPSEC-UV results with molecular weight standards of polyethylene glycol (0.6 kDa, 1 kDa, 6 kDa, 20 kDa). Polydispersity (d) of molecular weights was calculated with the equation of d = Mw/Mn. The fast Fourier infrared spectroscopy (FTIR) spectra (KBr, 1%) of samples were adopted by Spectrum 1B (Perkin Elmer, Waltham, MA, USA) between 4000 cm 1 and 400 cm 1. The excitation–emission matrix (EEM) was measured in a 1-cm cuvette using a Jasco FP-6500 spectrofluorometer (Tokyo, Japan) at 24 °C. The organic samples were diluted to 1 mg l 1 of DOC using 0.01 M KCl and acidified to pH 3 with 1 M HCl. A xenon lamp was the excitation source, and the excitation and emission slits were set to a 5 nm band-pass. Each EEM plot was generated by scanning excitation wavelengths from 220 nm to 400 nm with 5 nm steps and emitting fluorescence between 280 and 480 nm with 1 nm steps.
3. Results and discussion 3.1. Reactor performance
2.2. Extraction and fractionation of DOM The collected samples (original leachate and the effluents from A/O reactor and from MFC) were filtered by 0.45 lm cellulose nitrate membrane filter. The filtrate was diluted with 30 volumes of deionized water and then was acidified to pH 2 using HCl. The DOM in filtrates was fractionated using Amberlite XAD-8 and
The tested membraneless BES yielded a power curve with Pmax = 2.77 ± 0.26 W m 3 at 7.5 A m 3 (Supplementary materials). Correspondingly, the open circuit voltage (OCV) was noted high (743 ± 14 mV), correlating to the low Rint obtained (47.5 ± 1.4 X). These data suggested that the present BES was well operated with the fed leachate.
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G. Zhang et al. / Bioresource Technology 191 (2015) 350–354
100
B BES Reactor
A/O reactor
A/O Reactor
BES reactor
100
NH4+-N removal efficiencies
COD removal efficiency (%)
A
90
80
70
60 0
5
10
15
20
25
80
60
40
30
0
5
10
15
Time (d)
20
25
30
Time (d)
Fig. 1. Removal of COD (A) and NH+4-N (B) in BES reactor (Rext = 100 X) and A/O reactors fed with landfill leachate at loading rate of 3.0 kg COD m
The COD and NH+4 removals were shown in Fig. 1 for 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 components in the raw landfill 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 69.9 of 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,
Leachate A/O Effluent BES Effluent
DOC (mg L-1)
1500 900 600 300 0 HPO-A
TPI-A
HPO-N
A
28%
HPI
TPI-A
28%
23%
HPO-N
TPI-N 33%
HPI
13%
8%
11%
11% 12%
B
TPI-N
Fractions HPO-A
Leachate
21%
42%
22% 17%
d
1
.
all less than those by BES. Restated, both BES and A/O reactors preferably degraded hydrophilic and transphilic fractions in landfill leachate, with the former being performing better than the latter. The molecular weights of the five organic fractions in raw leachate, in BES effluent and in A/O reactor effluent were listed (Table 1). The BES and A/O reactors largely reduced Mw and Mn of all organic fractions in the raw leachate, with the former yielding slightly lower molecular weights of all fractions than the latter. The d value (Mw/Mn) 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 finding 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 1 mg 1): HPO-A (1.73 ± 0.1) > HPO-N (0.97 ± 0.08) > TPI-N (0.82 ± 0.09) > TPI-A
2100
1800
3
16%
A/O Effluent
15%
BES Effluent
Fig. 2. Fractional DOC distributions of the raw leachate, A/O effluent and BES effluent. DOC concentration (A) and ratios (B).
G. Zhang et al. / Bioresource Technology 191 (2015) 350–354 Table 1 Mean molecular weights and polydispersity of DOM fractions in the raw leachate, A/O effluent and BES effluent. Fraction
Mw (Da)
Mn (Da)
Polydispersity
Raw leachate HPO-A TPI-A HPO-N TPI-N HPI
97,800 4920 4810 3690 20,620
15,870 980 930 840 16,210
6.16 5.02 5.17 4.39 1.27
A/O effluent HPO-A TPI-A HPO-N TPI-N HPI
1710 1480 950 870 1440
1120 1150 620 610 1060
1.53 1.29 1.53 1.41 1.36
BES effluent HPO-A TPI-A HPO-N TPI-N HPI
1550 1490 840 750 1020
1090 1250 550 570 820
1.42 1.19 1.53 1.32 1.24
3.0
SUVA (L • m -1• mg -1)
byproduct-like (SMP-like) materials, respectively. The aromatic proteins and SMP-like substances predominated in the four fractions of the raw leachate except for the HPO-A, with the intensity following TPI-N > HPO-N > TPI-A > HPI. The A/O effluent had similar EEM profiles as those for raw leachate; while the BES effluent had a very different characteristic. All fractional EEM of the A/O effluents showed high fluorescent intensity in Regions II and IV, indicating that the A/O reactions were enriched with aromatic proteins and SMP-like substances. Conversely, the BES effluent 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 inffluents. 3.3. Role of bioelectrochemical reactions on cell performance
(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 effluents 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 effluents 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 landfill leachate. The FT-IR analysis (Supplementary materials) showed that all four organic fractions revealed signals between 3300 cm 1 and 3670 cm 1, attributing to stretch for hydroxyl groups. The absorption intensities in the A/O effluents were stronger than in the BES effluent, both were weaker than the raw leachate. The BES removed most 2950 cm 1 band (aliphatic CAH) in HPO-A and TPI-N fractions, 1600 cm 1 peak (C@C bond) in HPO-A and HPI-A fractions, and 1720 cm 1 (C@O bond), 1390–1420 cm 1 (OAH bond) and 1250–1050 cm 1 (hydrocarbon) in leachate. The A/O reactor also removed these peaks, but also yielded new peaks: 1190 cm 1 (CAO stretching), 1540 cm 1 (NAH bending), 1640 cm 1 (C@O stretching of amide), 810 cm 1 (CAH vibration or NAH out of plane). All five organic fractions of the raw landfill leachate had noticeable EEM peaks in Regions II, III and IV in Chen et al. (2003) (Supplementary materials), referring to the redundancy of aromatic proteins, fulvic acid-like components and soluble microbial
Row leachate A/O Effluent BES Effluent
2.5 2.0 1.5 1.0 0.5 0.0
353
HPO-A
TPI-A
HPO-N
TPI-N
The BES and A/O reactors favorably degraded hydrophilic and transphilic fractions in landfill 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 effluent from A/O reactor, conversely, contained large amounts of intermediates as evidenced by FTIR spectra. Restated, the bioelectrochemical reactions in BES accelerated COD degradation by enhancing conversion of hydrophilic and transphilic organic substances to CO2 or humins, leading to the noted high COD removal (84–89%). On the other hand, since the total electron quantity during the 30-d operation, estimated based on the current–time data, was 0.75 mol e . Meanwhile, the COD removed by BES was 315 g and the ammonium removal (to nitrate) was 21 g, accounting for 50.7 mol of electron transferred. Hence, the Columbic efficiency of the present leachate–BES was only 1.47%. This very low efficiency (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 efficiency for nitrogenous 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 field around the cathodic biofilm of BES stimulates the activity of the incorporated functional microorganisms, leading to high efficiencies of COD degradation and nitrification. The removal of high molecular weight and low aromaticity substances releases much inhibition on nitrifiers in biofilms, yielding high ammonium removal. Sufficient nitrate supply led to high denitrification rates in anodic compartment under anoxic environment. 4. Conclusions At Pmax of 2.77 ± 0.26 W m 3 at a current density of 7.5 A m 3, the biofilm of tested BES removed 86.3 ± 1.3% COD and 96.7 ± 0.9% NH+4-N at 3 kg COD m 3 d 1 volume loading, much higher than the control, an A/O reactor of identical geometry. The organic compounds preferably removed by BES followed 95.6% HPI, 87.6% TPI-A, 79.7% TPI-N, 75.5% HPO-A and 69.9% HPO-N, being of high molecular weights and low SUVA. The bioelectrochemical reactions did not directly degrade the organic substances; indirectly, the electric field thus generated at cathodic biofilm stimulates the microbial activity for enhanced COD removal and nitrification.
HPI
Fractions Fig. 3. Fractional SUVA distributions of the raw leachate, A/O effluent and BES effluent.
Acknowledgements The authors gratefully acknowledge funding from project 51408350 by National Nature Science Foundation of China, and
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project 2013125 supported by Scientific 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 http://dx.doi.org/10.1016/j.biortech.2015.05. 082. References APHA, Standards Methods for the Examination of Water and Wastewater, 20th ed., American Public Health Association, Washington, DC, USA, 1998. Chen, W., Westerhoff, P., Leenheer, J.A., Booksh, K., 2003. Fluorescence excitation– emission matrix regional integration to quantify spectra for dissolved organic matter. Environ. Sci. Technol. 37, 5701–5710. Chou, T.Y., Whiteley, C.G., Lee, D.J., 2014. Anodic potential on dual-chambered microbial fuel cell with sulphate reducing bacteria biofilm. Int. J. Hydrogen Energy 39, 19225–19231. Damiano, L., Jambeck, J.R., Ringelberg, D.B., 2014. Municipal solid waste landfill leachate treatment and electricity production using microbial fuel cells. Appl. Biochem. Biotechnol. 173, 472–485. Gálvez, A., Greenman, J., Ieropoulos, I., 2009. Landfill leachate treatment with microbial fuel cells; scale-up through plurality. Bioresour. Technol. 100, 5085– 5091. Ganesh, K., Jambeck, J.R., 2013. Treatment of landfill leachate using microbial fuel cells: alternative anodes and semi-continuous operation. Bioresour. Technol. 139, 383–387. Garner, L.E., Thomas, A.W., Sumner, J.J., Harvey, S.P., Bazan, G.C., 2012. Conjugated oligoelectrolytes increase current response and organic contaminant removal in wastewater microbial fuel cells. Energy Environ. Sci. 5, 9449–9452. Greenman, J., Gálvez, A., Giusti, L., Ieropoulos, I., 2009. Electricity from landfill leachate using microbial fuel cells: comparison with a biological aerated filter. Enzyme Microb. Technol. 44, 112–119.
Kjeldsen, P., Barlaz, M.A., Rooker, A.P., Baun, A., Ledin, A., Christensen, T.H., 2002. Present and long-term composition of MSW landfill leachate: a review. Crit. Rev. Environ. Sci. Technol. 32, 297–336. Lee, D.J., Liu, X., Weng, H.L., 2014. Sulfate and organic carbon removal by microbial fuel cell with sulfate-reducing bacteria and sulfide-oxidising bacteria anodic biofilm. Bioresour. Technol. 156, 14–19. Logan, B.E., Hamelers, B., Rozendal, R., Schröder, U., Keller, J., Freguia, S., Aelterman, P., Verstraete, W., Rabaey, K., 2006. Microbial fuel cells: methodology and technology. Environ. Sci. Technol. 40, 5181–5192. Özkaya, B., Cetinkaya, A.Y., Cakmakci, M., Karadag˘, D., Sahinkaya, E., 2013. Electricity generation from young landfill leachate in a microbial fuel cell with a new electrode material. Bioprocess Biosyst. Eng. 36, 399–405. Puig, S., Serra, M., Coma, M., Cabré, M., DolorsBalaguer, M., Colprim, J., 2011. Microbial fuel cell application in landfill leachate treatment. J. Hazard. Mater. 185, 763–767. Tugtas, A.E., Cavdar, P., Calli, B., 2013. Bio-electrochemical post-treatment of anaerobically treated landfill leachate. Bioresour. Technol. 128, 266–272. Vázquez-Larios, A.L., Solorza-Feria, O., Poggi-Varaldo, H.M., de Guadalupe GonzálezHuerta, R., Ponce-Noyola, M.T., Ríos-Leal, E., Rinderknecht-Seijas, N., 2014. Bioelectricity production from municipal leachate in a microbial fuel cell: effect of two cathodic catalysts. Int. J. Hydrogen Energy 39, 16667–16675. Wei, L.L., Zhao, Q.L., Hu, K., Lee, D.J., Xie, C.M., Jiang, J.Q., 2011. Extracellular biological organic matters in sewage sludge during mesophilic digestion at reduced hydraulic retention time. Water Res. 45, 1472–1480. You, S.J., Zhao, Q.L., Jiang, J.Q., Zhang, J.N., Zhao, S.Q., 2006. Sustainable approach for leachate treatment: electricity generation in microbial fuel cell. J. Environ. Sci. Health A 41, 2721–2734. Zhang, J.N., Zhao, Q.L., You, S.J., Jiang, J.Q., Ren, N.Q., 2008. Continuous electricity production from leachate in a novel upflow air–cathode membrane-free microbial fuel cell. Water Sci. Technol. 57, 1017–1021. Zhang, G.D., Zhao, Q.L., Jiao, Y., Lee, D.J., 2015a. Long-term operation of manuremicrobial fuel cell. Bioresour. Technol. 180, 365–369. Zhang, G.D., Jiao, Y., Lee, D.J., 2015b. A lab-scale anoxic/oxic–bioelectrochemical reactor for leachate treatments. Bioresour. Technol. 186, 97–105.
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Transformation of dissolved organic matters in landfill leachate–bioelectrochemical system Guodong Zhang a,b, Yan Jiao c, Duu-Jong Lee b,d,⇑ a
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 b
g r a p h i c a l a b s t r a c t
Bioelectrochemical system reactor
a r t i c l e
i n f o
Article history: Received 8 May 2015 Received in revised form 22 May 2015 Accepted 23 May 2015 Available online 28 May 2015 Keywords: Landfill leachate Microbial fuel cell Anoxic/oxic Dissolved organic matter Fractionation
800 Voltage
210
3.0
600
2.5
500
2.0
400
1.5
300 1.0 200 0.5
100
Leacha
180 150 90 60 30
0.0
0 0
2
4
6
8
10
Current density (A m-3)
12
14
0
HPO-A
TPI-A
HPO-N
TPI-N
HPI
a b s t r a c t A membraneless bioelectrochemical system (BES) reactor and an anoxic/oxic (A/O) reactor of identical configurations were applied to treat the landfill leachate (20,100 mg l 1 chemical oxygen demand (COD) and 1330 mg l 1 NH+4-N) at 24-h hydraulic retention time and 3 kg chemical oxygen demand m 3 d 1 volume loading. The BES with maximum power density of 2.77 ± 0.26 W m 3 and internal resistance of 47.5 ± 1.4 X 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 effluents from the BES and the A/O reactor were for the first time characterized and compared. The MFC preferentially degraded hydrophilic fraction (HPI) of the fed DOM and yielded excess humin with high aromaticity. The electric fields by bioelectrochemical reactions occurred at cathode stimulate the activities of COD degraders and nitrifiers in biofilms to enhance ammonium removals by BES reactor. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Landfill leachate is heavily polluted wastewater with complex dissolved organic matter, inorganic macro-components, heavy ⇑ Corresponding author at: Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan. Tel.: +886 2 23625632; fax: +886 2 23623040. E-mail address: [email protected] (D.-J. Lee). http://dx.doi.org/10.1016/j.biortech.2015.05.082 0960-8524/Ó 2015 Elsevier Ltd. All rights reserved.
Power density
700
Voltage (mV)
and anoxic/oxic reactor treated leachate. BES removed 84–89% COD and 94– 98% NH4+-N, much higher than A/O reactor. Dissolved organic matters in effluents from BES and A/O reactor were compared. BES converted hydrophilic fraction of the fed DOM to CO2 and excess humin. Electric fields at cathode assists ammonium removal by BES.
Power density (W m-3)
h i g h l i g h t s
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 generation from landfill 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; Özkaya et al., 2013; Ganesh and Jambeck,
G. Zhang et al. / Bioresource Technology 191 (2015) 350–354
2013; Vázquez-Larios et al., 2014; Damiano et al., 2014). These MFC studies noted 28–74% removal of chemical oxygen demand (COD) and 23–43% removal of NH+4 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 a 3.5-L membraneless MFC with biocathode, a bioelectrochemical system (BES), as a cost-effective device for leachate treatment. At 3 kg COD m 3 d 1 loading and 24-h hydraulic retention time (HRT), the tested membraneless BES could remove 90% of fed COD and 99% of NH+4 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 landfill leachate treatment, particularly on the almost complete removal of nitrogenous compounds 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 effluents from both reactors were characterized for the first time based on their hydrophobicity and acidity. We noted a low Columbic efficiency of the tested BES, as commonly noted for other liter-scale BES being reported. The possible mechanisms corresponding to the noted high ammonium 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 proposed by Zhang et al. (2015b). Briefly, both the BES and A/O reactor were consisted of a cylindrical anode compartment of diameter of 10 cm and height 20 cm, and a cathode compartment as the space outside the cylinder embraced by a cone of diameter 14 cm (bottom) and 25 cm (top) and of height 18 cm. Carbon fiber brushes embedded in graphite granules were filled 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 fixed resistance of 100 X while the latter was free from any external loading. Landfill leachates were collected from a landfill site at Taiyuan, China, with the following mean characteristics (in mg l 3): CODcr of 20,100, BOD5 of 9035, total organic carbon (TOC) of 7450, NH+4-N of 1330, total nitrogen (TN) of 1500, alkalinity of 6720, and pH 7.4. The leachate was fed to the inner cylindrical compartments at volume loading of 3 kg COD m 3 d 1. All experiments were conducted at room temperatures. The cone compartment was intermittently aerated at 500 ml min 1 in 30 min aeration + 90 min no-aeration cycles.
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XAD-4 resins into five organic fractions: hydrophobic acid (HPO-A), hydrophobic neutral (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI-N), and hydrophilic fraction (HPI). Briefly, 3000 ml of acidified filtrate was passed through XAD-8 and XAD-4 resin columns at a flow rate of 10 bed volumes per hour with the HPI was the organic matter in the XAD-4 effluent. Each of the resin columns was eluted backward with 0.1 M NaOH at a flow rate of 2 bed volumes per hour, followed by 2 bed volumes of milli-Q water. The elute from XAD-8 was the HPO-A, and that from XAD-4 was TPI-A. The HPO-N and TPI-N were those being respectively adsorbed on XAD-8 and XAD-4 resins 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 (+0.197 V vs. standard hydrogen electrode (SHE)) (model RE-5B, BASi, Ningbo, China). The volumetric 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 for 30 min at each resistance), from which the maximum power density (Pmax) was estimated (Logan et al., 2006). The internal resistance (Rint) of cell was determined from the slope of polarization curves. All DOM measurements were done in triplicate with the average and standard deviation being reported. The dissolved organic carbon (DOC) in the filtrate was analyzed using TOC-5000 Total Organic Carbon Analyzer (Shimadzu, Kyoto, Japan). The ultraviolet absorbance of samples was measured at 254 nm with a Shimadzu UV-2550 UV/VIS spectrophotometer (Shimadzu, Kyoto, Japan). The specific ultraviolet light absorbance (SUVA) was calculated as (UV-254/DOC) 100. The total COD (TCOD), total nitrogen (TN), NH+4-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 at 254 nm. Weight-average molecular weight (Mw) and number-average molecular weight (Mn) were calculated from the HPSEC-UV results with molecular weight standards of polyethylene glycol (0.6 kDa, 1 kDa, 6 kDa, 20 kDa). Polydispersity (d) of molecular weights was calculated with the equation of d = Mw/Mn. The fast Fourier infrared spectroscopy (FTIR) spectra (KBr, 1%) of samples were adopted by Spectrum 1B (Perkin Elmer, Waltham, MA, USA) between 4000 cm 1 and 400 cm 1. The excitation–emission matrix (EEM) was measured in a 1-cm cuvette using a Jasco FP-6500 spectrofluorometer (Tokyo, Japan) at 24 °C. The organic samples were diluted to 1 mg l 1 of DOC using 0.01 M KCl and acidified to pH 3 with 1 M HCl. A xenon lamp was the excitation source, and the excitation and emission slits were set to a 5 nm band-pass. Each EEM plot was generated by scanning excitation wavelengths from 220 nm to 400 nm with 5 nm steps and emitting fluorescence between 280 and 480 nm with 1 nm steps.
3. Results and discussion 3.1. Reactor performance
2.2. Extraction and fractionation of DOM The collected samples (original leachate and the effluents from A/O reactor and from MFC) were filtered by 0.45 lm cellulose nitrate membrane filter. The filtrate was diluted with 30 volumes of deionized water and then was acidified to pH 2 using HCl. The DOM in filtrates was fractionated using Amberlite XAD-8 and
The tested membraneless BES yielded a power curve with Pmax = 2.77 ± 0.26 W m 3 at 7.5 A m 3 (Supplementary materials). Correspondingly, the open circuit voltage (OCV) was noted high (743 ± 14 mV), correlating to the low Rint obtained (47.5 ± 1.4 X). These data suggested that the present BES was well operated with the fed leachate.
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100
B BES Reactor
A/O reactor
A/O Reactor
BES reactor
100
NH4+-N removal efficiencies
COD removal efficiency (%)
A
90
80
70
60 0
5
10
15
20
25
80
60
40
30
0
5
10
15
Time (d)
20
25
30
Time (d)
Fig. 1. Removal of COD (A) and NH+4-N (B) in BES reactor (Rext = 100 X) and A/O reactors fed with landfill leachate at loading rate of 3.0 kg COD m
The COD and NH+4 removals were shown in Fig. 1 for 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 components in the raw landfill 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 69.9 of 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,
Leachate A/O Effluent BES Effluent
DOC (mg L-1)
1500 900 600 300 0 HPO-A
TPI-A
HPO-N
A
28%
HPI
TPI-A
28%
23%
HPO-N
TPI-N 33%
HPI
13%
8%
11%
11% 12%
B
TPI-N
Fractions HPO-A
Leachate
21%
42%
22% 17%
d
1
.
all less than those by BES. Restated, both BES and A/O reactors preferably degraded hydrophilic and transphilic fractions in landfill leachate, with the former being performing better than the latter. The molecular weights of the five organic fractions in raw leachate, in BES effluent and in A/O reactor effluent were listed (Table 1). The BES and A/O reactors largely reduced Mw and Mn of all organic fractions in the raw leachate, with the former yielding slightly lower molecular weights of all fractions than the latter. The d value (Mw/Mn) 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 finding 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 1 mg 1): HPO-A (1.73 ± 0.1) > HPO-N (0.97 ± 0.08) > TPI-N (0.82 ± 0.09) > TPI-A
2100
1800
3
16%
A/O Effluent
15%
BES Effluent
Fig. 2. Fractional DOC distributions of the raw leachate, A/O effluent and BES effluent. DOC concentration (A) and ratios (B).
G. Zhang et al. / Bioresource Technology 191 (2015) 350–354 Table 1 Mean molecular weights and polydispersity of DOM fractions in the raw leachate, A/O effluent and BES effluent. Fraction
Mw (Da)
Mn (Da)
Polydispersity
Raw leachate HPO-A TPI-A HPO-N TPI-N HPI
97,800 4920 4810 3690 20,620
15,870 980 930 840 16,210
6.16 5.02 5.17 4.39 1.27
A/O effluent HPO-A TPI-A HPO-N TPI-N HPI
1710 1480 950 870 1440
1120 1150 620 610 1060
1.53 1.29 1.53 1.41 1.36
BES effluent HPO-A TPI-A HPO-N TPI-N HPI
1550 1490 840 750 1020
1090 1250 550 570 820
1.42 1.19 1.53 1.32 1.24
3.0
SUVA (L • m -1• mg -1)
byproduct-like (SMP-like) materials, respectively. The aromatic proteins and SMP-like substances predominated in the four fractions of the raw leachate except for the HPO-A, with the intensity following TPI-N > HPO-N > TPI-A > HPI. The A/O effluent had similar EEM profiles as those for raw leachate; while the BES effluent had a very different characteristic. All fractional EEM of the A/O effluents showed high fluorescent intensity in Regions II and IV, indicating that the A/O reactions were enriched with aromatic proteins and SMP-like substances. Conversely, the BES effluent 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 inffluents. 3.3. Role of bioelectrochemical reactions on cell performance
(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 effluents 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 effluents 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 landfill leachate. The FT-IR analysis (Supplementary materials) showed that all four organic fractions revealed signals between 3300 cm 1 and 3670 cm 1, attributing to stretch for hydroxyl groups. The absorption intensities in the A/O effluents were stronger than in the BES effluent, both were weaker than the raw leachate. The BES removed most 2950 cm 1 band (aliphatic CAH) in HPO-A and TPI-N fractions, 1600 cm 1 peak (C@C bond) in HPO-A and HPI-A fractions, and 1720 cm 1 (C@O bond), 1390–1420 cm 1 (OAH bond) and 1250–1050 cm 1 (hydrocarbon) in leachate. The A/O reactor also removed these peaks, but also yielded new peaks: 1190 cm 1 (CAO stretching), 1540 cm 1 (NAH bending), 1640 cm 1 (C@O stretching of amide), 810 cm 1 (CAH vibration or NAH out of plane). All five organic fractions of the raw landfill leachate had noticeable EEM peaks in Regions II, III and IV in Chen et al. (2003) (Supplementary materials), referring to the redundancy of aromatic proteins, fulvic acid-like components and soluble microbial
Row leachate A/O Effluent BES Effluent
2.5 2.0 1.5 1.0 0.5 0.0
353
HPO-A
TPI-A
HPO-N
TPI-N
The BES and A/O reactors favorably degraded hydrophilic and transphilic fractions in landfill 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 effluent from A/O reactor, conversely, contained large amounts of intermediates as evidenced by FTIR spectra. Restated, the bioelectrochemical reactions in BES accelerated COD degradation by enhancing conversion of hydrophilic and transphilic organic substances to CO2 or humins, leading to the noted high COD removal (84–89%). On the other hand, since the total electron quantity during the 30-d operation, estimated based on the current–time data, was 0.75 mol e . Meanwhile, the COD removed by BES was 315 g and the ammonium removal (to nitrate) was 21 g, accounting for 50.7 mol of electron transferred. Hence, the Columbic efficiency of the present leachate–BES was only 1.47%. This very low efficiency (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 efficiency for nitrogenous 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 field around the cathodic biofilm of BES stimulates the activity of the incorporated functional microorganisms, leading to high efficiencies of COD degradation and nitrification. The removal of high molecular weight and low aromaticity substances releases much inhibition on nitrifiers in biofilms, yielding high ammonium removal. Sufficient nitrate supply led to high denitrification rates in anodic compartment under anoxic environment. 4. Conclusions At Pmax of 2.77 ± 0.26 W m 3 at a current density of 7.5 A m 3, the biofilm of tested BES removed 86.3 ± 1.3% COD and 96.7 ± 0.9% NH+4-N at 3 kg COD m 3 d 1 volume loading, much higher than the control, an A/O reactor of identical geometry. The organic compounds preferably removed by BES followed 95.6% HPI, 87.6% TPI-A, 79.7% TPI-N, 75.5% HPO-A and 69.9% HPO-N, being of high molecular weights and low SUVA. The bioelectrochemical reactions did not directly degrade the organic substances; indirectly, the electric field thus generated at cathodic biofilm stimulates the microbial activity for enhanced COD removal and nitrification.
HPI
Fractions Fig. 3. Fractional SUVA distributions of the raw leachate, A/O effluent and BES effluent.
Acknowledgements The authors gratefully acknowledge funding from project 51408350 by National Nature Science Foundation of China, and
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