- Email: [email protected]
RETRACTED: Electricity harvest from wastewaters using microbial fuel cell with sulfide as sole electron donor
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 5 7 8 7 e1 5 7 9 1
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/he
Electricity harvest from wastewaters using microbial fuel cell with sulfide as sole electron donor Chin-Yu Lee a, Kuo-Ling Ho a, Duu-Jong Lee a,b,*, Ay Su c, Jo-Shu Chang d,e,f a
Department of Chemical Engineering, National Taiwan University, No 1, Sec 4, Roosevelt Road, Taipei, Taiwan Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan c Fuel Cell Center, Department of Mechanical Engineering, Yuan Ze University, Taoyuan 320, Taiwan d Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan e Center for Bioscience and Biotechnology, National Cheng Kung University, Tainan, Taiwan f Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan, Taiwan b
article info
abstract
Article history:
Toxicity prevents the bioenergy content of certain industrial effluents from being recov-
Received 3 December 2011
ered. In operation of microbial fuel cell (MFC), microorganisms can be inhibited with high
Received in revised form
levels of sulfides. This study applied a pure culture, an autotrophic denitrifier, Pseudomonas
18 March 2012
sp. C27, to start up a two-chambered MFC using sulfide as the sole electron donor. The
Accepted 20 March 2012
experimental results revealed that the MFC can successfully convert sulfide to elementary
Available online 11 April 2012
sulfur with electricity generation at a maximum power density of 29.3 mW m2. With no use of external organic carbon sources, the present device introduces a route for treating
Keywords:
sulfide laden wastewaters with electricity harvest.
Electricity
Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Toxicity Sulfide Microbial fuel cell
1.
Introduction
Industrial effluent with high toxicity is regarded as hazardous waste that must be decontaminated before it is disposed of. Harvesting bioenergy from toxic industrial effluents is of practical interest since biological processes are commonly assumed unable to convert the organic contents in toxic wastewaters into fuel. Hydrogen sulfide is one a common inorganic pollutant in wastewater from livestock farming [1]. High levels of sulfide ions in waters are hazardous to most living beings and needs to be removed from wastewater before discharged into environment. Sulfide treatment has conventionally been accomplished using physical, chemical,
electrochemical, and biological oxidation [2,3]. Physical and chemical techniques could effectively achieve sulfide removal, but could also incur high operation and sludge disposal costs. Fuel cell presents as a key component to future hydrogen economy. Microbial fuel cells (MFC) provide a new approach for waste treatment, and especially deliver the potential to directly generate electricity from degradation of organic and inorganic substrates in wastewater (1). Sulfide removal in MFC was studied [4e11]. Ryckelynck et al. [12] showed that sulfide oxidation is one of the key players in electricity generation in sedimentary microbial fuel cells. Rabaey et al. [13] cultivated mixed sulfide-oxidizing bacteria in MFC system
* Corresponding author. Department of Chemical Engineering, National Taiwan University, No 1, Sec 4, Roosevelt Road, Taipei, Taiwan. Fax: þ886 2 23625632. E-mail addresses: [email protected], [email protected] (D.-J. Lee). 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.03.114
15788
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 5 7 8 7 e1 5 7 9 1
for simultaneous sulfide removal and electricity generation. These authors noted that the Alcaligenes sp. and Paracoccus sp. play important roles in sulfide oxidation. Sun et al. [13] demonstrated that bacterial catalysis played an important role in the electricity generation from a sulfide-fed MFC with anaerobic sludge. Sun et al. [14] investigated the microbial communities in MFC for sulfide conversion and electricity generation. These authors revealed that the exoelectrogenic, sulfur-oxidizing and sulfate-reducing bacteria can harvest electricity during sulfide oxidation. In general, the MFC systems applied for sulfide removal were conducted using organic substrates as carbon sources. Strains isolated from mature anodic biofilms could only yield low powers when was cultured alone [15]. Logan [16] proposed some synergistic interactions should exist in a mixed exoelectrogenic community so the high power from MFC can be realized. This study isolated a functional autotrophic denitrifier, Pseudomonas sp. C27, from an expanded granular sludge bed reactor treating sulfide-rich wastewater and utilized this stain to start up a two-chambered MFC using sulfide as the sole electron donor. The strain has a higher sulfide degradation rate than those reported in literature. The power generated from the sulfide-MFC was recorded.
2.
Materials and methods
2.1.
Inoculum and MFC
A strain was isolated from an expanded granular sludge bed (EGSB) reactor operated by Chen et al. [17] that treated sulfiderich wastewater for more than one year. The pure culture was used to start up a two-chambered MFC using sulfide as the sole electron donor. The DNA of the strain was isolated following the procedure of [18]; the strain was identified by 16S rDNA sequencing using 11F (50 -GTT TGA TCM TGG CTC AG-30 ) and 1512R (50 -ACG GCT ACC TTG TTA CGA CT-30 ). The DNA was amplified using an eppendorf mastercycler (Eppendorf AG, Hamburg, Germany) by denaturation at 94 C for 3 min with 35 cycles of 94 C for 30 s, 54 C for 60 s, 72 C for 90 s, and a final extension at 72 C for 7 min. The PCR-amplified 16S rDNA was sequenced using the ABI Prism model 3730 (version 3.2) DNA sequencer. The isolated strain was identified as Pseudomonas sp. C27 (16S rRNA sequence deposited to GenBank under accession number GQ241351). Two-chamber MFCs comprising anode and cathode cylindrical chambers (inside diameter, 5 cm; length, 4 cm each) was connected to a cation exchange membrane (CEM) (Ultrex CMI7000; Membrane International, Inc., Glen Rock, NJ, USA). Anode was made of carbon felt (area, 6 cm2), cathode was made of carbon cloth (area, 9 cm2) (W0S1002; CeTech Co., Taichung, Taiwan). The cathode had a surface loading of 0.5 mg cm2 Pt catalyst. The electrodes were placed at the centers of each chamber and were parallel to the CEM.
2.2.
Startup and operation
The enriched C27consortium was fed into the MFC anodic chamber for cultivation in medium (per L)e1 ml Wolfe’s
vitamin solution, 2 ml Wolfe’s mineral solution with pH adjusted to 8.0. The cathodic medium was a mixture of 50 mM PBS buffer (pH 6.9) and 50 mM K3Fe(CN)6. The MFC was inoculated with 10 ml of Pseudomonas sp. C27 culture at 30 C. Sulfide was added to a final concentration of 100 ppm after the anodic chamber was sparged with N2 for 5 min to remove O2 in solution. After MFC startup, the synthetic wastewater was fed to the anodic chamber containing (per l) 2.0 g NaHCO3; 1.0 g NH4Cl; 1.8 g KH2PO4; 1.2 g K2HPO4 and 10 ml of trace element. The wastewater pH was adjusted to 8.0 0.1 using 1 N NaOH or HCl. The cathode chamber was filled with 50 mM PBS buffer (pH 6.9) and 50 mM K3Fe(CN)6. Ag/AgCl reference electrode was used to record the individual electrode potential. The MFC was operated in fed-batch mode. Different sulfide concentrations were added to the anode solution of MFCs in batch tests. An abiotic reactor with a sterile anode was operated as control. All electrochemical experiments and MFC operations reported in this study were carried out in duplicate at 30 C and only the mean values were reported. Residual sulfide, pH and metabolite composition in waters were determined at each time point.
2.3.
Electrochemical analysis
Voltage cross the 1 kU resistor was recorded at an interval of 2 min using a digital acquisition system (611D, CH Instruments Inc., USA). Current density was normalized by the projected surface areas of anodic sides. Polarization curves were measured by applying a linear potential decrease of 1 mVs1 from the open circuit voltage to 0 mV. Coulombic efficiency was calculated by dividing coulomb output (integrating current and time) by total coulomb input (based on sulfide or acetate) according to previous literature [14]. Sulfide concentration was determined by potential titration using Sure-Flow Combination Silver/Sulfide Electrodes. Concentrations of sulfate, thiosulfate and sulfite were measured using an ion chromatography (Dionex ICS-3000). Elemental sulfur on the anode electrode was imaged with a scanning electronic microscopy (Nova NanoSEM 230) at the end of batch tests according to the protocol described by Chung et al. [19,20]. The pH was measured by a pH meter. All tests were repeated at least three times for data assurance.
3.
Results and discussion
3.1.
Cell performance
Fig. S1 (in Supplementary Data) shows the current profiles of abiotic reactors in batch tests. The abiotic reactors fed with synthetic wastewater containing different concentrations of sulfide (50150 ppm). Electricity was generated immediately after the addition of sulfide. However, the current could not sustain but rapidly decline. For instance, upon addition of 150 ppm sulfide, the cell voltage was increased to 70 mV, and then rapidly dropped below 10 mV after 1.5 d of operation. About 40.7% of sulfide was converted to thiosulfate (Fig. S2 in Supplementary Data); since minimal quantity of sulfate was produced, the elemental sulfur production rate was estimated as 57.6%. According to the sulfide metabolite distributions, the
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 5 7 8 7 e1 5 7 9 1
15789
coulombic efficiency of the abiotic cells for conversion of sulfide was only 3.2%.
3.2.
Effects of sulfide concentrations
Fig. 1 shows the voltage and current of the tested MFC. The voltage and current both were increased right after sulfide dosage, which gradually declined over time. The power outputs for biotic cells were much higher than the abiotic cells. For instance, at 150 mgl1 S2, the maximum potential and current density of MFC were 65 mV and 108 mA m2, respectively. Then, the cell was maintained at 56 mV and 95 mA m2 for one day. The time evolution of cell performance of the tested MFC and the control resembled the reported [14]. The thiosulfate (31.7%), sulfite (6.6%) and elementary sulfur (60.2%) were the primary metabolites. The polarization and power-current curves of the MFC at different sulfide concentrations are shown in Fig. 2. The electricity output and power density increased with increasing sulfide concentration. The maximum power densities and open-circle voltages in sulfide concentration at 30, 80 and 150 mgl1 were 8.2, 19.1 and 29.3 mW m2, and 600, 670 and 669 mV, respectively. Compared with the abiotic reactor, the present MFC-C27 system delivered higher and
Fig. 2 e Polarization curves (a) and power density curves (b) for the tested MFC at different sulfide concentrations.
more sustainable power by microbial catalysis. As the mean power delivery was increased with sulfide concentration, the present MFC-C27 can harvest electricity from wastewater with sulfide as the sole electron donor with no apparent inhibition at up to 150 mgl1 S2. The Coulombic efficiency was calculated based on sulfur compound distribution as 25.6%, much higher than control (3.2%). The loss in efficiency may be attributable to the oxygen leakage through the membrane in the MFC [21,22]. Tests with changing sulfide concentrations were conducted (Fig. 3). Although with data fluctuation, the cell voltage was increased with increasing sulfide concentration, after peaking the voltage at 650 mV at 150 mgl1 S2, the voltage dropped with reduced sulfide concentration. The yielded biofilm revealed reversibility upon change in sulfide concentrations.
3.3. Effects of electrode materials and organic carbon sources Fig. 1 e Cell performance at different sulfide concentrations. (a) Cell potential, (b) cell current.
Tests with carbon cloth or carbon felt as anodic materials were conducted (Fig. 4). Apparently the cell voltage with
15790
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 5 7 8 7 e1 5 7 9 1
Fig. 3 e Reversibility of cell performance at different sulfide concentrations.
Fig. 5 e Cell performance with different carbon sources. 150 mglL1 S2L.
50.9 mW m2. With acetate, the MFC has poor removal of COD and the maximum power density was 32 mW m2 only. carbon cloth as anodic materials was higher than that with carbon felt. Such an observation correlates with the understanding that mature biofilm needs extended electrode surface to attach on. The carbon cloth provides more surface area than carbon felt, hence presenting superior cell performance than the latter. Organic substances exist frequently in wastewaters. Liu [23] demonstrated that pure culture Pseudomonas sp. C27 can utilize alcohol, organic acid and carbohydrates as carbon sources for growth, with alcohol as the preferred one. Restated, the strain C27 can also conduct heterotrophic pathway. Tests with 150 mgl1 S2 and added ethanol or acetate were performed (Fig. 5). With ethanol, the MFC can maintain an output voltage up to six days with chemical oxygen demand (COD) for ethanol being reduced by 15.7%. Fig. S3 shows the polarization curve for the S2- with ethanol system. The OCV was 696 mV while the maximum power density was
3.4.
Harvesting of electricity from toxic wastewater
To harvest bioenergy from toxic influent is relevant on both resource recovery and environmental protection perspectives [24e26]. The results presented in this study revealed the potential of the present C27 strain to harvest electricity from toxic (sulfide-containing) industrial effluent. Besides the electricity generated from the MFC, the sulfide was converted to less toxic products, such as elementary sulfur. Hence, the present MFC can be an autotrophic unit to effectively treat sulfide-containing wastewaters. On the other hand, tests in Sec 3.3 demonstrated the possible interference of organic substances on cell performance. Care should be taken in handling wastewater properties beyond understanding the lumped parameter such as COD in influent.
4.
Conclusions
In this study, the MFC system inoculated with autotrophic denitrifier Pseudomonas sp. C27 has been successfully applied to treat sulfide in wastewater, yielding a maximum power density of 29.3 mW m2. Sulfide was nearly completely removed from the wastewater during the MFC operation and electrochemically oxidized to elemental sulfur and other sulfur compounds by the anode. The MFCC27 system has potential to generate electricity from sulfide-containing wastewater without the addition of external carbon sources.
Acknowledgments
Fig. 4 e Cell performance with different anodic materials. 150 mglL1 S2L.
This work was financially supported by the National Taiwan University (Toward Top University Project) and project NSFC No. 51176037.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 5 7 8 7 e1 5 7 9 1
Appendix A. Supplementary material Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.ijhydene.2012. 03.114.
references
[1] Rai C, Taylor M. Microbial sweetening of sour natural gas using mixed cultures. Environ Progr 1996;15:6e11. [2] Chen C, Ren NQ, Wang AJ, Liu L, Lee DJ. Enhanced performance of denitrifying sulfide removal process under micro-aerobic condition. J Hazard Mater 2010;179:1147e51. [3] Pikaar I, Rozendal RA, Yuan ZG, Keller J, Rabaey K. Electrochemical sulfide removal from synthetic and real wastewater at high current densities. Water Res 2011;45:2281e9. [4] Habermann W, Pommer EH. Biological fuel cells with sulphide storage capacity. Appl Microbiol Biotechnol 1991;35: 128e33. [5] Cooney MJ, Roschi E, Marison IW, Comninellis C, Stockar UV. Physiologic studies with the sulfate-reducing bacterium Desulfovibrio desulfuricans: Evaluation for use in a biofuel cell. Enzym Microbiol Technol 1998;18:358e65. [6] Wang YR, Yan HQ, Wang E. The electrochemical oxidation and the quantitative determination of hydrogen sulfide on a solid polymer electrolyte-based system. J Electroanal Chem 2001;497:163e7. [7] Tender LM, Reimers CE, Stecher HA, Holmes DE, Bond DR, Lowy DA, et al. Harvesting microbially generated power on the seafloor. Nat Biotechnol 2002;20:821e5. [8] Ryckelunck N, Stecher HA, Reimers CE. Understanding the anodic mechanism of a seafloor fuel cell: interactions between geochemistry and microbial activity. Biogeochem 2005;76:113e39. [9] Zhang BG, Zhao HZ, Shi CH, Zhou SG, Ni JR. Simultaneous removal of sulfide and organics with vanadium(V) reduction in microbial fuel cells. J Chem Technol Biotechnol 2009;84: 1780e6. [10] Zhang BG, Zhao HZ, Zhou SG, Shi CH, Wang C, Ni JR. A novel UASB-MFC-BAF integrated system for high strength molasses wastewater treatment and bioelectricity generation. Bioresour Technol 2009;100:5687e93. [11] Nielsen ME, Wu DM, Girguis PR, Reimers CE. Influence of substrate on electron transfer mechanisms in chambered benthic microbial fuel cell. Environ Sci Technol 2009;43: 8671e7.
15791
[12] Rabaey K, Van de Sompel K, Maignien L, Boon N, Aelterman P, Clauwaert P, et al. Microbial fuel cells for sulfide removal. Environ Sci Technol 2006;40:5218e24. [13] Sun M, Mu ZX, Chen YP, Sheng GP, Liu XW, Chen YZ, et al. Microbe-assisted sulfide oxidation in the anode of a microbial fuel cell. Environ Sci Technol 2009;43:3372e7. [14] Sun M, Tong ZH, Sheng GP, Chen YZ, Zhang F, Mu ZX, et al. Microbial communities involved in electricity generation from sulfide oxidation in a microbial fuel cell. Biosens Bioelectron 2010;26:470e6. [15] Zuo Y, Xing D, Regan JM, Logan BE. Isolation of the exoelectrogenic bacterium Ochrobactrum anthropi YZ-1 by using a U-tube microbial fuel cell. Appl Environ Microbiol 2006;74:3130e7. [16] Logan BE. Exoelectrogenic bacteria that power microbial fuel cells. Nat Rev Microbiol 2009;7:375e81. [17] Chen C, Wang AJ, Ren NQ, Lee DJ, Lai JY. High-rate denitrifying sulfide removal process in expanded granular sludge bed reactor. Bioresour Technol 2009;100:2316e9. [18] Adav SS, Lin JCT, Yang Z, Whiteley CG, Lee DJ, Peng XF, et al. Stereological assessment of extracellular polymeric substances, exo-enzymes, and specific bacterial strains in bioaggregates using fluorescence experiments. Biotechnol Adv 2010;28:255e80. [19] Chung YC, Ho KL, Tseng CP. Treatment of high H2S concentration by chemical absorption and biological oxidation process. Environ Eng Sci 2006;23:942e53. [20] Chung YC, Lin YY, Tseng CP. Operational characteristics of effective removal of H2S and NH3 waste gases by activated carbon biofilter. J Air Waste Manage Assoc 2004; 54:450e8. [21] Liu H, Ramnarayanan R, Logan BE. Production of electricity during wastewater treatment using a single chamber microbial fuel cell. Environ Sci Technol 2004;38:2281e5. [22] Kim JR, Min B, Logan BE. Evaluation of procedures to acclimate a microbial fuel cell for electricity production. Appl Microbiol Biotechnol 2005;68:23e30. [23] Liu FC. Use of heterotrophic denitrifier pseudomonas sp. C27 to achieve simultaneous removal of sulfide, nitrate and organic carbon. Master thesis. National Taiwan University; 2010. [24] Lee DJ, Tai J, Adav SS, Su A. Harvesting biohydrogen from toxic wastewater using isolated strain. Int J Hydrogen Energy 2011;36:13907e13. [25] Tai J, Adav SS, Su A, Lee DJ. Biological hydrogen produced from phenol-containing wastewater using Clostridium butyricum. Int J Hydrogen Energy 2010;35:13345e9. [26] Ho KL, Chen YY, Lee DJ. Biohydrogen production from cellobiose in phenol and cresol-containing medium using Clostridium sp. R1. Int J Hydrogen Energy 2010;35:10239e44.
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/he
Electricity harvest from wastewaters using microbial fuel cell with sulfide as sole electron donor Chin-Yu Lee a, Kuo-Ling Ho a, Duu-Jong Lee a,b,*, Ay Su c, Jo-Shu Chang d,e,f a
Department of Chemical Engineering, National Taiwan University, No 1, Sec 4, Roosevelt Road, Taipei, Taiwan Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan c Fuel Cell Center, Department of Mechanical Engineering, Yuan Ze University, Taoyuan 320, Taiwan d Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan e Center for Bioscience and Biotechnology, National Cheng Kung University, Tainan, Taiwan f Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan, Taiwan b
article info
abstract
Article history:
Toxicity prevents the bioenergy content of certain industrial effluents from being recov-
Received 3 December 2011
ered. In operation of microbial fuel cell (MFC), microorganisms can be inhibited with high
Received in revised form
levels of sulfides. This study applied a pure culture, an autotrophic denitrifier, Pseudomonas
18 March 2012
sp. C27, to start up a two-chambered MFC using sulfide as the sole electron donor. The
Accepted 20 March 2012
experimental results revealed that the MFC can successfully convert sulfide to elementary
Available online 11 April 2012
sulfur with electricity generation at a maximum power density of 29.3 mW m2. With no use of external organic carbon sources, the present device introduces a route for treating
Keywords:
sulfide laden wastewaters with electricity harvest.
Electricity
Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Toxicity Sulfide Microbial fuel cell
1.
Introduction
Industrial effluent with high toxicity is regarded as hazardous waste that must be decontaminated before it is disposed of. Harvesting bioenergy from toxic industrial effluents is of practical interest since biological processes are commonly assumed unable to convert the organic contents in toxic wastewaters into fuel. Hydrogen sulfide is one a common inorganic pollutant in wastewater from livestock farming [1]. High levels of sulfide ions in waters are hazardous to most living beings and needs to be removed from wastewater before discharged into environment. Sulfide treatment has conventionally been accomplished using physical, chemical,
electrochemical, and biological oxidation [2,3]. Physical and chemical techniques could effectively achieve sulfide removal, but could also incur high operation and sludge disposal costs. Fuel cell presents as a key component to future hydrogen economy. Microbial fuel cells (MFC) provide a new approach for waste treatment, and especially deliver the potential to directly generate electricity from degradation of organic and inorganic substrates in wastewater (1). Sulfide removal in MFC was studied [4e11]. Ryckelynck et al. [12] showed that sulfide oxidation is one of the key players in electricity generation in sedimentary microbial fuel cells. Rabaey et al. [13] cultivated mixed sulfide-oxidizing bacteria in MFC system
* Corresponding author. Department of Chemical Engineering, National Taiwan University, No 1, Sec 4, Roosevelt Road, Taipei, Taiwan. Fax: þ886 2 23625632. E-mail addresses: [email protected], [email protected] (D.-J. Lee). 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2012.03.114
15788
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 5 7 8 7 e1 5 7 9 1
for simultaneous sulfide removal and electricity generation. These authors noted that the Alcaligenes sp. and Paracoccus sp. play important roles in sulfide oxidation. Sun et al. [13] demonstrated that bacterial catalysis played an important role in the electricity generation from a sulfide-fed MFC with anaerobic sludge. Sun et al. [14] investigated the microbial communities in MFC for sulfide conversion and electricity generation. These authors revealed that the exoelectrogenic, sulfur-oxidizing and sulfate-reducing bacteria can harvest electricity during sulfide oxidation. In general, the MFC systems applied for sulfide removal were conducted using organic substrates as carbon sources. Strains isolated from mature anodic biofilms could only yield low powers when was cultured alone [15]. Logan [16] proposed some synergistic interactions should exist in a mixed exoelectrogenic community so the high power from MFC can be realized. This study isolated a functional autotrophic denitrifier, Pseudomonas sp. C27, from an expanded granular sludge bed reactor treating sulfide-rich wastewater and utilized this stain to start up a two-chambered MFC using sulfide as the sole electron donor. The strain has a higher sulfide degradation rate than those reported in literature. The power generated from the sulfide-MFC was recorded.
2.
Materials and methods
2.1.
Inoculum and MFC
A strain was isolated from an expanded granular sludge bed (EGSB) reactor operated by Chen et al. [17] that treated sulfiderich wastewater for more than one year. The pure culture was used to start up a two-chambered MFC using sulfide as the sole electron donor. The DNA of the strain was isolated following the procedure of [18]; the strain was identified by 16S rDNA sequencing using 11F (50 -GTT TGA TCM TGG CTC AG-30 ) and 1512R (50 -ACG GCT ACC TTG TTA CGA CT-30 ). The DNA was amplified using an eppendorf mastercycler (Eppendorf AG, Hamburg, Germany) by denaturation at 94 C for 3 min with 35 cycles of 94 C for 30 s, 54 C for 60 s, 72 C for 90 s, and a final extension at 72 C for 7 min. The PCR-amplified 16S rDNA was sequenced using the ABI Prism model 3730 (version 3.2) DNA sequencer. The isolated strain was identified as Pseudomonas sp. C27 (16S rRNA sequence deposited to GenBank under accession number GQ241351). Two-chamber MFCs comprising anode and cathode cylindrical chambers (inside diameter, 5 cm; length, 4 cm each) was connected to a cation exchange membrane (CEM) (Ultrex CMI7000; Membrane International, Inc., Glen Rock, NJ, USA). Anode was made of carbon felt (area, 6 cm2), cathode was made of carbon cloth (area, 9 cm2) (W0S1002; CeTech Co., Taichung, Taiwan). The cathode had a surface loading of 0.5 mg cm2 Pt catalyst. The electrodes were placed at the centers of each chamber and were parallel to the CEM.
2.2.
Startup and operation
The enriched C27consortium was fed into the MFC anodic chamber for cultivation in medium (per L)e1 ml Wolfe’s
vitamin solution, 2 ml Wolfe’s mineral solution with pH adjusted to 8.0. The cathodic medium was a mixture of 50 mM PBS buffer (pH 6.9) and 50 mM K3Fe(CN)6. The MFC was inoculated with 10 ml of Pseudomonas sp. C27 culture at 30 C. Sulfide was added to a final concentration of 100 ppm after the anodic chamber was sparged with N2 for 5 min to remove O2 in solution. After MFC startup, the synthetic wastewater was fed to the anodic chamber containing (per l) 2.0 g NaHCO3; 1.0 g NH4Cl; 1.8 g KH2PO4; 1.2 g K2HPO4 and 10 ml of trace element. The wastewater pH was adjusted to 8.0 0.1 using 1 N NaOH or HCl. The cathode chamber was filled with 50 mM PBS buffer (pH 6.9) and 50 mM K3Fe(CN)6. Ag/AgCl reference electrode was used to record the individual electrode potential. The MFC was operated in fed-batch mode. Different sulfide concentrations were added to the anode solution of MFCs in batch tests. An abiotic reactor with a sterile anode was operated as control. All electrochemical experiments and MFC operations reported in this study were carried out in duplicate at 30 C and only the mean values were reported. Residual sulfide, pH and metabolite composition in waters were determined at each time point.
2.3.
Electrochemical analysis
Voltage cross the 1 kU resistor was recorded at an interval of 2 min using a digital acquisition system (611D, CH Instruments Inc., USA). Current density was normalized by the projected surface areas of anodic sides. Polarization curves were measured by applying a linear potential decrease of 1 mVs1 from the open circuit voltage to 0 mV. Coulombic efficiency was calculated by dividing coulomb output (integrating current and time) by total coulomb input (based on sulfide or acetate) according to previous literature [14]. Sulfide concentration was determined by potential titration using Sure-Flow Combination Silver/Sulfide Electrodes. Concentrations of sulfate, thiosulfate and sulfite were measured using an ion chromatography (Dionex ICS-3000). Elemental sulfur on the anode electrode was imaged with a scanning electronic microscopy (Nova NanoSEM 230) at the end of batch tests according to the protocol described by Chung et al. [19,20]. The pH was measured by a pH meter. All tests were repeated at least three times for data assurance.
3.
Results and discussion
3.1.
Cell performance
Fig. S1 (in Supplementary Data) shows the current profiles of abiotic reactors in batch tests. The abiotic reactors fed with synthetic wastewater containing different concentrations of sulfide (50150 ppm). Electricity was generated immediately after the addition of sulfide. However, the current could not sustain but rapidly decline. For instance, upon addition of 150 ppm sulfide, the cell voltage was increased to 70 mV, and then rapidly dropped below 10 mV after 1.5 d of operation. About 40.7% of sulfide was converted to thiosulfate (Fig. S2 in Supplementary Data); since minimal quantity of sulfate was produced, the elemental sulfur production rate was estimated as 57.6%. According to the sulfide metabolite distributions, the
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 5 7 8 7 e1 5 7 9 1
15789
coulombic efficiency of the abiotic cells for conversion of sulfide was only 3.2%.
3.2.
Effects of sulfide concentrations
Fig. 1 shows the voltage and current of the tested MFC. The voltage and current both were increased right after sulfide dosage, which gradually declined over time. The power outputs for biotic cells were much higher than the abiotic cells. For instance, at 150 mgl1 S2, the maximum potential and current density of MFC were 65 mV and 108 mA m2, respectively. Then, the cell was maintained at 56 mV and 95 mA m2 for one day. The time evolution of cell performance of the tested MFC and the control resembled the reported [14]. The thiosulfate (31.7%), sulfite (6.6%) and elementary sulfur (60.2%) were the primary metabolites. The polarization and power-current curves of the MFC at different sulfide concentrations are shown in Fig. 2. The electricity output and power density increased with increasing sulfide concentration. The maximum power densities and open-circle voltages in sulfide concentration at 30, 80 and 150 mgl1 were 8.2, 19.1 and 29.3 mW m2, and 600, 670 and 669 mV, respectively. Compared with the abiotic reactor, the present MFC-C27 system delivered higher and
Fig. 2 e Polarization curves (a) and power density curves (b) for the tested MFC at different sulfide concentrations.
more sustainable power by microbial catalysis. As the mean power delivery was increased with sulfide concentration, the present MFC-C27 can harvest electricity from wastewater with sulfide as the sole electron donor with no apparent inhibition at up to 150 mgl1 S2. The Coulombic efficiency was calculated based on sulfur compound distribution as 25.6%, much higher than control (3.2%). The loss in efficiency may be attributable to the oxygen leakage through the membrane in the MFC [21,22]. Tests with changing sulfide concentrations were conducted (Fig. 3). Although with data fluctuation, the cell voltage was increased with increasing sulfide concentration, after peaking the voltage at 650 mV at 150 mgl1 S2, the voltage dropped with reduced sulfide concentration. The yielded biofilm revealed reversibility upon change in sulfide concentrations.
3.3. Effects of electrode materials and organic carbon sources Fig. 1 e Cell performance at different sulfide concentrations. (a) Cell potential, (b) cell current.
Tests with carbon cloth or carbon felt as anodic materials were conducted (Fig. 4). Apparently the cell voltage with
15790
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 5 7 8 7 e1 5 7 9 1
Fig. 3 e Reversibility of cell performance at different sulfide concentrations.
Fig. 5 e Cell performance with different carbon sources. 150 mglL1 S2L.
50.9 mW m2. With acetate, the MFC has poor removal of COD and the maximum power density was 32 mW m2 only. carbon cloth as anodic materials was higher than that with carbon felt. Such an observation correlates with the understanding that mature biofilm needs extended electrode surface to attach on. The carbon cloth provides more surface area than carbon felt, hence presenting superior cell performance than the latter. Organic substances exist frequently in wastewaters. Liu [23] demonstrated that pure culture Pseudomonas sp. C27 can utilize alcohol, organic acid and carbohydrates as carbon sources for growth, with alcohol as the preferred one. Restated, the strain C27 can also conduct heterotrophic pathway. Tests with 150 mgl1 S2 and added ethanol or acetate were performed (Fig. 5). With ethanol, the MFC can maintain an output voltage up to six days with chemical oxygen demand (COD) for ethanol being reduced by 15.7%. Fig. S3 shows the polarization curve for the S2- with ethanol system. The OCV was 696 mV while the maximum power density was
3.4.
Harvesting of electricity from toxic wastewater
To harvest bioenergy from toxic influent is relevant on both resource recovery and environmental protection perspectives [24e26]. The results presented in this study revealed the potential of the present C27 strain to harvest electricity from toxic (sulfide-containing) industrial effluent. Besides the electricity generated from the MFC, the sulfide was converted to less toxic products, such as elementary sulfur. Hence, the present MFC can be an autotrophic unit to effectively treat sulfide-containing wastewaters. On the other hand, tests in Sec 3.3 demonstrated the possible interference of organic substances on cell performance. Care should be taken in handling wastewater properties beyond understanding the lumped parameter such as COD in influent.
4.
Conclusions
In this study, the MFC system inoculated with autotrophic denitrifier Pseudomonas sp. C27 has been successfully applied to treat sulfide in wastewater, yielding a maximum power density of 29.3 mW m2. Sulfide was nearly completely removed from the wastewater during the MFC operation and electrochemically oxidized to elemental sulfur and other sulfur compounds by the anode. The MFCC27 system has potential to generate electricity from sulfide-containing wastewater without the addition of external carbon sources.
Acknowledgments
Fig. 4 e Cell performance with different anodic materials. 150 mglL1 S2L.
This work was financially supported by the National Taiwan University (Toward Top University Project) and project NSFC No. 51176037.
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 7 ( 2 0 1 2 ) 1 5 7 8 7 e1 5 7 9 1
Appendix A. Supplementary material Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.ijhydene.2012. 03.114.
references
[1] Rai C, Taylor M. Microbial sweetening of sour natural gas using mixed cultures. Environ Progr 1996;15:6e11. [2] Chen C, Ren NQ, Wang AJ, Liu L, Lee DJ. Enhanced performance of denitrifying sulfide removal process under micro-aerobic condition. J Hazard Mater 2010;179:1147e51. [3] Pikaar I, Rozendal RA, Yuan ZG, Keller J, Rabaey K. Electrochemical sulfide removal from synthetic and real wastewater at high current densities. Water Res 2011;45:2281e9. [4] Habermann W, Pommer EH. Biological fuel cells with sulphide storage capacity. Appl Microbiol Biotechnol 1991;35: 128e33. [5] Cooney MJ, Roschi E, Marison IW, Comninellis C, Stockar UV. Physiologic studies with the sulfate-reducing bacterium Desulfovibrio desulfuricans: Evaluation for use in a biofuel cell. Enzym Microbiol Technol 1998;18:358e65. [6] Wang YR, Yan HQ, Wang E. The electrochemical oxidation and the quantitative determination of hydrogen sulfide on a solid polymer electrolyte-based system. J Electroanal Chem 2001;497:163e7. [7] Tender LM, Reimers CE, Stecher HA, Holmes DE, Bond DR, Lowy DA, et al. Harvesting microbially generated power on the seafloor. Nat Biotechnol 2002;20:821e5. [8] Ryckelunck N, Stecher HA, Reimers CE. Understanding the anodic mechanism of a seafloor fuel cell: interactions between geochemistry and microbial activity. Biogeochem 2005;76:113e39. [9] Zhang BG, Zhao HZ, Shi CH, Zhou SG, Ni JR. Simultaneous removal of sulfide and organics with vanadium(V) reduction in microbial fuel cells. J Chem Technol Biotechnol 2009;84: 1780e6. [10] Zhang BG, Zhao HZ, Zhou SG, Shi CH, Wang C, Ni JR. A novel UASB-MFC-BAF integrated system for high strength molasses wastewater treatment and bioelectricity generation. Bioresour Technol 2009;100:5687e93. [11] Nielsen ME, Wu DM, Girguis PR, Reimers CE. Influence of substrate on electron transfer mechanisms in chambered benthic microbial fuel cell. Environ Sci Technol 2009;43: 8671e7.
15791
[12] Rabaey K, Van de Sompel K, Maignien L, Boon N, Aelterman P, Clauwaert P, et al. Microbial fuel cells for sulfide removal. Environ Sci Technol 2006;40:5218e24. [13] Sun M, Mu ZX, Chen YP, Sheng GP, Liu XW, Chen YZ, et al. Microbe-assisted sulfide oxidation in the anode of a microbial fuel cell. Environ Sci Technol 2009;43:3372e7. [14] Sun M, Tong ZH, Sheng GP, Chen YZ, Zhang F, Mu ZX, et al. Microbial communities involved in electricity generation from sulfide oxidation in a microbial fuel cell. Biosens Bioelectron 2010;26:470e6. [15] Zuo Y, Xing D, Regan JM, Logan BE. Isolation of the exoelectrogenic bacterium Ochrobactrum anthropi YZ-1 by using a U-tube microbial fuel cell. Appl Environ Microbiol 2006;74:3130e7. [16] Logan BE. Exoelectrogenic bacteria that power microbial fuel cells. Nat Rev Microbiol 2009;7:375e81. [17] Chen C, Wang AJ, Ren NQ, Lee DJ, Lai JY. High-rate denitrifying sulfide removal process in expanded granular sludge bed reactor. Bioresour Technol 2009;100:2316e9. [18] Adav SS, Lin JCT, Yang Z, Whiteley CG, Lee DJ, Peng XF, et al. Stereological assessment of extracellular polymeric substances, exo-enzymes, and specific bacterial strains in bioaggregates using fluorescence experiments. Biotechnol Adv 2010;28:255e80. [19] Chung YC, Ho KL, Tseng CP. Treatment of high H2S concentration by chemical absorption and biological oxidation process. Environ Eng Sci 2006;23:942e53. [20] Chung YC, Lin YY, Tseng CP. Operational characteristics of effective removal of H2S and NH3 waste gases by activated carbon biofilter. J Air Waste Manage Assoc 2004; 54:450e8. [21] Liu H, Ramnarayanan R, Logan BE. Production of electricity during wastewater treatment using a single chamber microbial fuel cell. Environ Sci Technol 2004;38:2281e5. [22] Kim JR, Min B, Logan BE. Evaluation of procedures to acclimate a microbial fuel cell for electricity production. Appl Microbiol Biotechnol 2005;68:23e30. [23] Liu FC. Use of heterotrophic denitrifier pseudomonas sp. C27 to achieve simultaneous removal of sulfide, nitrate and organic carbon. Master thesis. National Taiwan University; 2010. [24] Lee DJ, Tai J, Adav SS, Su A. Harvesting biohydrogen from toxic wastewater using isolated strain. Int J Hydrogen Energy 2011;36:13907e13. [25] Tai J, Adav SS, Su A, Lee DJ. Biological hydrogen produced from phenol-containing wastewater using Clostridium butyricum. Int J Hydrogen Energy 2010;35:13345e9. [26] Ho KL, Chen YY, Lee DJ. Biohydrogen production from cellobiose in phenol and cresol-containing medium using Clostridium sp. R1. Int J Hydrogen Energy 2010;35:10239e44.