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Simultaneous production of bioelectricity and treatment of membrane concentrate in multitube microbial fuel cell
Journal of Bioscience and Bioengineering VOL. 122 No. 5, 594e600, 2016 www.elsevier.com/locate/jbiosc
Simultaneous production of bioelectricity and treatment of membrane concentrate in multitube microbial fuel cell Emre Oguz Koroglu,* Afsin Y. Cetinkaya, Bestami Ozkaya, and Ahmet Demir Yildiz Technical University, Department of Environmental Engineering, 34220, Esenler, Istanbul, Turkey Received 25 December 2015; accepted 8 April 2016 Available online 30 April 2016
The performance of upflow multitube microbial fuel cell (UM2FC) from membrane concentrate of domestic wastewater (50% concentrate or a volume to concentration ratio of 2) has been investigated in a laboratory test. The test found that the UM2FC with the tin-coated copper mesh and coil spring under different hydraulic retention times (HRTs) produced maximum electricity of 916 ± 200 mW/m3 (61 mW/m2) at an HRT of 0.75 day with a 78% soluble chemical oxygen demand (sCOD) removal efficiency and 3% and 20% Coulombic efficiencies (CEs). The whole-cell resistance as calculated from the Nyquist plot and equivalent circuit were approximately 134 and 255 U for HRTs of 0.5 and 0.75 days, respectively. Considering HRT, the current increase with longer HRT could be due to longer contact time between organic material and biofilm, which results in a higher electrical efficiency. The results showed that UM2FC could represent an effective system for simultaneous membrane concentrate treatment and electricity production after further improvements on MFC and operating conditions. Ó 2016, The Society for Biotechnology, Japan. All rights reserved. [Key words: Tubular microbial fuel cell; Multielectrode connection; Electrochemical impedance spectroscopy; Surface morphology; Membrane concentrate]
Microbial fuel cells (MFCs) are microbiological systems that can be used in wastewater treatment for energy recovery and biomass reduction. The studies conducted in the last decade have focused on effective MFC design and economical electrode and separator materials. Optimizing the other operating conditions is also another important approach to improve the performance of MFCs. The MFC design, electrode performance, external operating conditions, resistance, and rate of substrate degradation principally increase the power output from MFCs (1,2). Much effort is being devoted to more effective and applicable MFC design and materials. Tubular MFC designs have attracted much attention recently to make the MFCs feasible to scale up and improve electrical performance. For example, tubular MFCs with spiral spacers were developed by creating a helical flow to increase electricity generation and investigated in both laboratory and on-site tests (3). The energy production in the tubular MFCs ranged from 0.071 to 0.073 kWh/kg chemical oxygen demand (COD), and it was proved to be an effective approach to improve energy production. In this study, an upflow multitube microbial fuel cell (UM2FC) was tested for its ability to simultaneously treat concentrate streams of domestic wastewater and produce electricity (4). The pipe-in-pipe electrode assemblies and compact design represented a new treatment technology for membrane concentrate treatment as well as electricity generation. A tubular configuration makes it possible to
* Corresponding author. Yildiz Technical University, Faculty of Civil Engineering, Department of Environmental Engineering, Davutpasa Campus, 34220 Esenler, Istanbul, Turkey. Tel.: þ90 212 383 54 02; fax: þ90 212 383 51 02. E-mail address: [email protected] (E.O. Koroglu).
achieve distribution close to optimal spatial distribution of anode, cathode, and separator in an MFC. A granular carbon anode MFC with an external cathode surrounding the vertical upflow containment tube was considered by Rabaey et al. (5). Maximum and average power densities of 90 and 52 W/m3 were obtained with acetate at an organic loading rate (OLR) of 1.1 kg COD/m3/day. A similar configuration of tubular reactor was investigated with an open-air biocathode generating 65 W/m3 of power density at an OLR of 1.5 kg COD/m3/day (6). A recent development of tubular MFCs has aimed to optimize operating conditions to increase the production of electricity and understand electrochemical behavior of cells and physical properties such as surface morphology and elemental analysis. Li et al. (7) tested the feasibility of bioelectricity production from animal carcass wastewater under different hydraulic retention times (HRTs). After a start-up period of approximately 55 days, when HRT was set at 3 days, MFC showed best bioelectricity performance with the maximum power density of 2.19 W/m3 and minimum internal resistance of 30.3 U. Increasing HRT from 3 to 6 days increased COD and nitrate removal efficiency, but reduced the rate of production of ammonia. Kim et al. (8) investigated the energy recovery using longitudinal tubular MFC reactors with influent sucrose OLRs between 0.04 and 0.42 g COD/l/day. The maximum energy production was 1.75 Wh/g COD at an OLR of 0.24 g/l/day and Coulombic efficiency (CE) ranged from 9% to 92%. Therefore, the tubular MFC design is promising for wastewater treatment and electricity generation. Nevertheless, the disposal and treatment of membrane concentrates besides wastewater is a serious problem that constrains the application of membrane technology (9). MFCs could represent
1389-1723/$ e see front matter Ó 2016, The Society for Biotechnology, Japan. All rights reserved. http://dx.doi.org/10.1016/j.jbiosc.2016.04.002
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an effective system for membrane concentrate treatment and electricity production simultaneously. The feasibility of membrane concentrate treatment and electricity production has not been considerably tested in the MFCs. Koroglu et al. (4) studied the generation of electricity from membrane concentrate using a UM2FC. In this study, different electrode materials were installed in a tubular MFC differently from Koroglu et al. (4) with the same substrate and inoculum. The objectives of this study were to (i) investigate the performance of UM2FC for electricity generation and wastewater treatment from membrane concentrate; (ii) investigate the effect of HRT; (iii) evaluate the electrochemical behavior of UM2FC and identify the distribution of the internal resistance; and (iv) investigate the surface morphology, dispersion, and functional groups by scanning electronic microscopy (SEM) and attenuated total reflectioneFourier transform infrared (ATReFTIR) spectroscopy. MATERIALS AND METHODS Reactor configuration and operation In this study, a patented (by Turkish Patent Institute with number of TR-201106609B) tubular UM2FC was used with a tin-coated mesh (LessEMF, USA) as anodeecathode electrode, stainless steel coil spring (0.5-mm wire diameter, 5-mm outer diameter, and 1.1 103-U cm1 electrical resistivity) to obtain a mechanical support between mesh electrodes, cylindrical glass reactor, and a tubular Nafion (Perma Pure) membrane. The volume of the anode chamber was 100 ml and the total surface area of the electrodes was 15 cm2. The electrodes were constructed by entwining the membrane over spring and rolling up tin-coated copper meshes around the springs (Fig. 1). Five electrode configurations were connected in parallel by a titanium wire with 100-U external resistance and their electrical responses were monitored together. Before setting up the electrode, membranes were pretreated in accordance with Koroglu et al. (4) described previously by sequential immersion in a 30% volume fraction H2O2 solution, 49.04 g L1 H2SO4 solution, and deionized water at 85 C for 1 h. During the initial start-up period, the UM2FC was inoculated with a sediment _ sample (2:10 v:v) obtained from Golden Horn in Istanbul, Turkey, and the anodic liquid was collected from the ISKI Domestic Wastewater Pretreatment Plant in Yenikapi (41 000 09.2800 N 28 560 56.8700 E). The UM2FC was operated for approximately 48 h until the desired current generation and biofilm formation were observed. The cathode chambers were recirculated continuously with oxygensaturated distilled water. The experimental setup was the same as that of Koroglu et al. (4). The reactor was operated in batch mode at room temperature (20 2 C) with raw domestic wastewater and anodic liquid was recirculated via a circulating pump to produce gentle shear on the surface of the anode to obtain an active biofilm. After 48 h of enrichment and adaptation period, the UM2FC switched to continuous mode with concentrated wastewater with an HRT of 0.75e0.5 day. The molecular weight (MW) distribution analysis and membrane concentrate production using
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membrane filtration were done as described by Koroglu et al. (4) using a stirred filtration apparatus (Amicon-8400, Merck Millipore) under 200-kPa absolute pressure for MW distribution analysis and a laboratory scale cross-flow mode filtration apparatus with a flat sheet membrane system for membrane concentrate production of domestic wastewater. The 50% retained ratio or a volume concentration ratio (VCR) of 2 was used in this study, and the former represents the percentage ratio of filtered wastewater volume to initial feed volume or VCR was used to express the degree of concentration of a target compound, as shown by the following equation: VCR ¼ CF ¼
Vp V0 ¼ 1þ Vr Vr
(1)
where V0 is the initial feed tank volume, Vp is the volume of the permeate, and Vr is the volume retained (10). The characteristics of the domestic wastewater and membrane concentrate were: pH 6.9 0.8, conductivity 900 300 mS m1, soluble chemical oxygen demand (sCOD) 480 70 g m3, and total suspended solid (TSS) 240 28 g m3 for raw wastewater and pH 7.2 0.0, conductivity 950 210 mS m1, sCOD 685 31 g m3, and TSS 348 24 g m3 for 50% concentrate stream. Measurement and analysis The electrochemical impedance spectroscopy (EIS) analysis represents the limiting factors as internal resistance in MFCs and in this study, internal resistance of UM2FC cell was segmented in various specific resistances such as Ohmic resistance (RU), anodic charge transfer resistance (Ra), cathodic charge transfer resistance (Rc), and constant phase element (CPE) as a component of equivalent electrical circuit. The impedance data of the UM2FC were analyzed by fitting them to an equivalent electrical circuit model. The magnitude of the impedance can be expressed in terms of the real and imaginary components, as given in Eq. 3: jZj ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Z 2r þ Z 2j
(2)
Electrochemical measurements were monitored by a computer-based potentiostat system (Ludre L02/V01, Ludre Software, Istanbul, Turkey) every 5 min (4). EIS data were recorded on a Ludre potentiostat in a frequency range of 100 kHz to 1 MHz and amplitude of 10 mV. The impedance spectra were recorded when the maximum power was observed, because the power reaches its maximum values as a result of the maximum biochemical conversion rate. The internal resistances were calculated by fitting and simulating the experimental data with equivalent circuits using the ZsimpWin 3.22 software (11). The concentrations of sCOD and TSS were measured using the standard methods (method 5220 D and 2540 D). All samples for SCOD measurements were filtered through 0.45-mm syringe filters (polyvinylidene difluoride (PVDF), 25 mm, Restek). Measurement of pH and conductivity was made using a probe (WTW Multi 3420, Germany) after sampling. CE was calculated as given by Logan (12): CE ¼
Ms $I F$bes $q$DC
(3)
where Ms is the MW of the substrate added, I is the circuit current, F is the Faraday’s constant, bes is the number of electrons exchanged per mole of oxygen, q is the flow rate, and DC is the difference between the influent and effluent CODs.
FIG. 1. Configuration of UM2FC: (A) tin-coated copper mesh; (B) stainless steel coil springs; and (C) the assembled UM2FC for the test.
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FIG. 2. Power density and COD removal outputs as a function of time at different stages.
FTIR spectral analysis was performed to determine the changes in microstructure of Perma Pure membrane using an ATR method in IR spectrometer by a Watson 1000 FTIR apparatus at ambient temperature. The membranes were pressed against the crystal using a pressure applicator at the maximum setting. Spectra were acquired for 100 scans between 400 and 4000 cm1 at a resolution of 16 cm1. These spectra were analyzed in more detail for chemical shifts and peaks. SEM and energy dispersive X-ray spectrometry (EDX) analyses was carried out using an Apollo-300 Cam Scan scanning electron microscope to determine the morphology of membranes. The film surface was sputter-coated with gold (Polaron range). Then, elements in the membranes before and after beer water are determined by EDX.
RESULTS AND DISCUSSION Electricity generation and treatment performance The reactor configuration was similar to previous configuration and no significant change was observed; therefore, the configuration and results were compared with the previous reactor (4). The 100-U power density generation at external resistance and different HRTs was monitored in the UM2FC for 37 days (Fig. 2). It was observed that the UM2FC produced unstable electrical current
FIG. 3. Impedance spectra and equivalent circuit exploited for the fitting of the impedance spectra for the UM2FC with different operating conditions.
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TABLE 1. Fit parameters for spectra of the UM2FC at different operating conditions. HRT
Ra (U)
Rc (U)
Rs (U)
CPEa (U1sN)
CPEc (U1sN)
Rint (U)
0.5 0.75
61.93 144.9
63.16 101.2
8.84 9.13
0.01501 0.00896
0.01338 0.01107
133.93 255.23
density, mostly varying between 20 and 600 mA/m2. The power densities for different HRTs were 916 200 mW/m3 or 61 mW/ m2 (HRT 0.75 day) and 22 4 mW/m3 or 12 mW/m2 (HRT 0.5 day). The results are higher (0e260 mA/m2) than those obtained from a tubular multitube MFC (4), but much lower (2e60 W/m3) than laboratory-scale tubular MFCs (5,13). The increase of the OLR influenced direct anodic oxidation in UM2FC; hence, the power density was increased. Direct anodic oxidation might activate the oxidation species on the anode surface through bioelectrochemical reactions, which would facilitate oxidation of organic compounds in wastewater and lead to enhanced electricity production. The observed high power output can be attributed to the availability of a higher substrate concentration to sustain metabolic activity (14). There was an electrical problem in the laboratory between days 18 and 22, during which the reactor was fed manually in batch mode, leading to a decrease in UM2FC performance. Then, the operation mode was switched again to continuous mode, and steady-state conditions were obtained in 4e5 days. When the HRT was decreased to 0.5 day, a sharp decrease on the UM2FC performance was observed. Clearly, the HRT of 0.75 day for this type of reactor was beneficial for electricity generation. Considering HRT of 0.75 and 0.5 days, the current increase with longer HRT could be due to higher contact time between organic material and biofilm, and that results in higher electrical efficiency (15). The unstable current density and power density compared with Rabaey et al. (5) may be because the substrate used in this study has low organic constituent or more complex compounds such as recalcitrants. The laboratory tests generally use easily degradable
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substrates in anode, such as glucose, and that results in higher efficiencies in MFCs. The other reason might be biofouling on the membrane surface. Because of the nature and membrane concentrate of the domestic wastewater, biofilm quickly formed on the anode surface and results in membrane fouling. Over the range of HRT tests, the overall sCOD removal efficiency ranged from 40% to 78% for UM2FC (Fig. 2). The maximum sCOD removal efficiencies were 78% and 58% for HRTs of 0.75 and 0.5 days, respectively. Although the sCOD removal efficiency in UM2FC was lower than that of activated sludge systems, the UM2FC produced much less sludge. The CEs of different HRTs were found to vary between 3% and 20%. It has been reported that approximately 20% of the COD removal is practically related to electricity production (16). The maximum CE based on sCOD removal ranged from 10% to 20% at HRT of 0.75 day. The obtained CE was >0.3 0.04% for a pilot-scale multianode/cathode MFC of 16-L capacity (17) and 3 1.2% using domestic wastewater for a stackable pilot MFC of 250-L capacity at an Rext of 2 U (18). However, the results are lower than 38e49% CE for tubular MFC using sucrose wastewater with a reactor volume of 220 ml (8). This lower CE was attributed to several factors such as fermentation and complexity of the substrate. However, the domestic wastewater used in this study can be easy biodegraded. Oxygen diffusion to the anode chamber through Perma Pure membrane could possibly be another reason for the reduced energy conversion (19). The whole-cell resistances calculated from the Nyquist plot and equivalent circuit (Fig. 3) were approximately 134 and 255 U for HRTs of 0.5 and 0.75 days (Table 1). As given in Table 1, anodic and cathodic charge transfer resistances and Ohmic resistance increased, and as a result, total internal resistance decreased with the decrease of HRT from 0.75 to 0.5 day. The internal resistance at an HRT of 0.75 day was 90% higher than that at an HRT of 0.5 day. The increase of internal resistance was caused by 61.95% anodic charge transfer resistance, 28.40% cathodic charge transfer resistance, and 0.22% Ohmic resistance.
FIG. 4. SEM images of the membrane surfaces populated with bacterial cells: (A) pure membrane (1000); (B) used membrane (20,000); and (C) used membrane (5000).
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Anodic charge transfer resistance showed a 57% decrease by switching the HRT from 0.75 to 0.5 day, and this attributes majorly to the increase in internal resistance. The possible reason of increased anodic and cathodic charge transfer resistances might be the lack of electron transfer between bacteria and electrode and hence a decrease in chemical reaction in anode and cathode. Thus, the major factor in the increase of the total internal resistance could be related to a decrease in chemical reaction occurring in anode. SEM and EDX analyses Analysis of SEM images provided more detailed information about the conditions of the pure and used membrane surfaces (20,21). Fig. 4 shows the SEM images of pure and used membranes surfaces. The pure membranes had a uniform surface morphology, and no cracks and pores were observed. As shown in Fig. 4, the microbial community is attached to the membrane surfaces with a uniform morphology and different cations are formed on the surface of membranes used by the UM2FC. The results of EDX analysis for pure and used membranes are shown in Fig. 5. The EDX analysis showed the presence of some inorganic salt precipitations on the used membranes. Fig. 5 shows the composition of particles on the membrane surface. Chemical analysis of the top layer of pure membrane film
by EDX analysis shows that the surface contains carbon (C) and fluorine (F). The different elements present on the surface of used membranes are carbon (C), oxygen (O), fluorine (F), calcium (Ca), copper (Cu), and silicon (Si). It can be seen that these elements are evenly distributed on the membrane surface. These observations can be explained by the biofilms on the membrane surfaces. SEM and EDX analyses revealed that fouling of the membrane surface was attributed to the presence of bacteria in cation and anion, microorganisms from fungi mixture, extracellular microbial polymers, and the inorganic salt (21,22). The formed biofilms constitute a physical barrier against protons from the anode side to the cathode side during the pass of protons. During the formation of biofilm, the electrical resistance and pH gradient of the MFC are increased, which resulted in a loss of performance (23,24). SEM, EDX, and ATReFTIR analyses revealed that fouling on the anode surface was explained with the decrease in migration of protons (24,25). FTIR analysis Infrared spectra of both anode and cathode sides of the membrane are shown in Fig. 6 as pure and used. Water is present in the structure of membranes in both free and connected forms. The free water was usually located in the region between 3700 and 3080 cm1 (Fig. 6) and presented as monomeric H2O molecules. However, the bound water was found
FIG. 5. EDX spectra of membranes used in UM2FC: (A) pure membrane and (B) used membrane.
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FIG. 6. ATReFTIR spectra of membranes.
in the porous structure and it was difficult to remove (22,26,27). This band hydrophilicity and conductivity of membrane were attributed to the increase of HeO stretching in the free SO3H group (28). In Fig. 6, the S]O (1410 cm1) and SeOH (910 cm1) stretching bands of the eSO3H group are observed. AmideI band as an indicator of proteins were located in the region between 1600 ile 1650 cm1 which was not seen this band (20). It is evident from the figure that the membranes were observed at 1300 and 1056 cm1 due to asymmetric and symmetric SO 3 stretching. Although the strong CeF stretching bands were shrouded, the presence of SO 3 stretching bands and humidity sensing can be evidenced with the transfer of proton (29). This group of bands can provide information about proton transfer, proton transport, and the mechanism involved. The strong bands centered at 1300 and 1100 cm1 were attributed to CF stretching band (30). Furthermore, it is observed as attributed to the CeOeC linkage between the backbone and side chain (Fig. 6) (30). The ATReFTIR spectra of the anode and cathode surface of the used membrane are compared in Fig. 6. A shift to low frequency and a decrease in intensity of the OH stretching band on anode and only a shift to low frequency on cathode surface compared with pure membrane were determined. In a fuel cell system, it is well known that this type of decrease of intensity of the OH stretching band is directly proportional to the decrease in membrane conductivity and OH groups (28,31). The shifting of bands can be shown as a result of microbial contamination (31). The magnitudes of shifting in anode and cathode were determined to be 54 and 173 cm1. A remarkable decrease of the peak magnitude was observed at 2950 cm1 in anode compared with cathode. The magnitudes of the asymmetrical and symmetrical eSO 3 stretching bands were decreased in anode and disappeared and shifted to a low frequency (1029 cm1) in cathode. A new peak was observed in anode at 855 cm1, which was attributed to a biofilm layer on membrane surface. The results showed that biofilm layer was organic-based and the structure of the layer contained carbon (C), oxygen (O), sulfide (S), thiol (SeH) and disulfide (SeS). In this study, tin-coated copper mesh and coil spring made from stainless steel were tested as electrode materials in UM2FC design. These materials showed satisfactory results, but unstable electricity production comparable to a previous study. It is concluded that utilization of MFC with mesh and spring significantly reduces the internal resistance. Results obtained from the system were among the higher values reported earlier. The design also provided a sustainable solution to membrane concentrate treatment over 70% COD removal. However, its efficacy should be further studied.
ACKNOWLEDGMENTS The authors gratefully acknowledge the Scientific and Technological Research Council of Turkey (TUBITAK) (Project No. 111Y252) for financial support and Istanbul Water and Sewage Administration (ISKI) for providing wastewater. They also thank Dr. Cenk Denktas and Dr. Derya Yılmaz Baysoy for their valuable comments.
References 1. Zhou, M., Chi, M., Luo, J., He, H., and Jin, T.: An overview of electrode materials in microbial fuel cells, J. Power Source, 196, 4427e4435 (2011). 2. Liu, H., Cheng, S., and Logan, B. E.: Power generation in fed-batch microbial fuel cells as a function of ionic strength, temperature, and reactor configuration, Environ. Sci. Technol., 39, 5488e5493 (2005). 3. Zhang, F., Ge, Z., Grimaud, J., Hurst, J., and He, Z.: Improving electricity production in tubular microbial fuel cells through optimizing the anolyte flow with spiral spacers, Bioresour. Technol., 134, 251e256 (2013). 4. Koroglu, E. O., Baysoy, D. Y., Cetinkaya, A. Y., Ozkaya, B., and Cakmakcı, M.: Novel design of a multitube microbial fuel cell (UM2FC) for energy recovery and treatment of membrane concentrates, Biomass Bioenergy, 69, 58e65 (2014). 5. Rabaey, K., Lissens, G., and Verstraete, W.: Microbial fuel cells: performances and perspectives. Biofuels for fuel cells: renewable energy from biomass fermentation, pp. 377e399. IWA Publishing, London (2005). 6. Clauwaert, P., Van der Ha, D., Boon, N., Verbeken, K., Verhaege, M., Rabaey, K., and Verstraete, W.: Open air biocathode enables effective electricity generation with microbial fuel cells, Environ. Sci. Technol., 41, 7564e7569 (2007). 7. Li, X., Zhu, N., Wanga, Y., Li, P., Wua, P., and Wua, J.: Animal carcass wastewater treatment and bioelectricity generation in up-flow tubular microbial fuel cells: effects of HRT and non-precious metallic catalyst, Bioresour. Technol., 128, 454e460 (2013). 8. Kim, J. R., Premier, G. C., Hawkes, F. R., Rodríguez, J., Dinsdale, R. M., and Guwyb, A.: Modular tubular microbial fuel cells for energy recovery during sucrose wastewater treatment at low organic loading rate, Bioresour. Technol., 101, 1190e1198 (2010). 9. Sperlich, A., Warschke, D., Wegmann, C., Ernst, M., and Jekel, M.: Treatment of membrane concentrates: phosphate removal and reduction of scaling potential, Water Sci. Technol., 61, 301e306 (2010). 10. Wang, L. K., Chen, J. P., Hung, Y. T., and Shammas, N. K.: Membrane and desalination technologies, pp. 433e476. Springer, New York (2011). 11. Cheng, K., He, D., Peng, T., Lu, H., Pan, M., and Mu, S.: Porous grapheme supported Pt catalysts for proton exchange membrane fuel cells, Electrochim. Acta, 132, 356e363 (2014). 12. Logan, B. E.: Microbial fuel cell, 1st ed. John Wiley & Sons Inc., Hoboken (2008). 13. Zhang, F., Jacobson, K. S., Torres, P., and He, Z.: Effects of anolyte recirculation rates and catholytes on electricity generation in a liter-scale upflow microbial fuel cell, Energy Environ. Sci., 3, 1347e1352 (2010). 14. Mohan, S. V., Raghavulu, S. V., Peri, D., and Sarma, P. N.: Integrated function of microbial fuel cell (MFC) as bioelectrochemical treatment system associated with bioelectricity generation under higher substrate load, Biosens. Bioelectron., 24, 2021e2027 (2009).
600
KOROGLU ET AL.
15. Sharma, Y. and Li, B.: Optimizing energy harvest in wastewater treatment by combining anaerobic hydrogen producing biofermentor (HPB) and microbial fuel cell (MFC), Int. J. Hydrog. Energy, 35, 3789e3797 (2010). 16. He, Z. and Mansfeld, F.: Exploring the use of electrochemical impedance spectroscopy (EIS) in microbial fuel cell studies, Energy Environ. Sci., 2, 215e219 (2009). 17. Jiang, D., Curtis, M., Troop, E., Scheible, K., McGrath, J., Hu, B., Suib, S., Raymond, D., and Li, B.: Pilot-scale study on utilizing multi-anode/cathode microbial fuel cells (MAC MFCs) to enhance the power production in wastewater treatment, Int. J. Hydrog. Energy, 36, 876e884 (2011). 18. Feng, Y., He, W., Liu, J., Wang, X., Qu, Y., and Ren, N.: A horizontal plug flow and stackable pilot microbial fuel cell for municipal wastewater treatment, Bioresour. Technol., 156, 132e138 (2014). 19. Nandy, A., Kumar, V., Mondal, S., Dutta, K., Salah, M., and Kundu, P.: Performance evaluation of microbial fuel cells: effect of varying electrode configuration and presence of a membrane electrode assembly, New Biotechnol., 32, 272e281 (2015). 20. Rabiller-Baudry, M., Gouttefangeas, F., Le Lannic, J., and Rabiller, P.: Coupling of SEM-EDX and FTIR-ATR to (quantitatively) investigate organic fouling on porous organic composite membranes, pp. 1066e1076, in: MéndezVilas, A. (Ed.), Current microscopy contributions to advances in science and technology. Formatex, Badajoz (2012). 21. Ping, Q., Cohen, B., Dosoretz, C., and He, Z.: Long-term investigation of fouling of cation and anion exchange membranes in microbial desalination cells, Desalination, 325, 48e55 (2013). 22. Xu, J., Sheng, G. P., Luo, H., Li, W., Wang, L., and Yu, H.: Fouling of proton exchange membrane (PEM) deteriorates the performance of microbial fuel cell, Water Res., 46, 1817e1824 (2012). 23. Leong, J. X., Dauda, W. R., Ghasemi, M., Liew, K. B., and Ismail, M.: Ion exchange membranes as separators in microbial fuel cells for bioenergy
J. BIOSCI. BIOENG.,
24.
25.
26.
27.
28.
29.
30.
31.
conversion: a comprehensive review, Renew. Sustain. Energy Rev., 28, 575e587 (2013). Chung, K., Fujiki, I., and Okabe, S.: Effect of formation of biofilms and chemical scale on the cathode electrode on the performance of a continuous two-chamber microbial fuel cell, Bioresour. Technol., 102, 355e360 (2011). Chae, K. J., Choi, M., Ajayi, G. F., Park, W., Chang, I. S., and Kim, I. S.: Mass transport through a proton exchange membrane (Nafion) in microbial fuel cells, Energy Fuel, 22, 169e176 (2008). Noto, V. D., Piga, M., Giffin, S., Lavina, E. S., Smotkin, J. Y., and Sanchez, C.: Influence of anions on proton-conducting membranes based on neutralized nafion 117, triethylammonium methanesulfonate, and triethylammonium perfluorobutanesulfonate, J. Phys. Chem., 116, 1361e1369 (2012). Belfer, S., Fainchtain, R., Purinson, Y., and Kedem, O.: Surface characterization by FTIR-ATR spectroscopy of polyethersulfone membranes-unmodified, modified and protein fouled, J. Membr. Sci., 172, 113e124 (2000). Ghasemi, M., Daud, W. R., Ismail, M., Rahimnejad, M., Ismail, A., Leong, J., Miskan, M., and Liew, K.: Effect of pre-treatment and biofouling of proton exchange membrane on microbial fuel cell performance, Int. J. Hydrog. Energy, 38, 5480e5484 (2013). Wu, R., Sun, Y., Lin, C., Chen, H., and Chavali, M.: Composite of TiO2 nanowires and nafion as humidity sensor material, Sens. Actuators, 115, 198e204 (2006). Danilczuk, M., Lin, S., Schlick, S., and Hamrock, M.: Understanding the fingerprint region in the infra-red spectra of perfluorinated ionomer membranes and corresponding model compounds: experiments and theoretical calculations, J. Power Source, 196, 8216e8224 (2011). Barbora, L., Singhb, R., Shrotib, N., and Verma, A.: Synthesis and characterization of neodymium oxide modified nafion membrane for direct alcohol fuel cells, Mater. Chem. Phys., 122, 211e216 (2010).
Simultaneous production of bioelectricity and treatment of membrane concentrate in multitube microbial fuel cell Emre Oguz Koroglu,* Afsin Y. Cetinkaya, Bestami Ozkaya, and Ahmet Demir Yildiz Technical University, Department of Environmental Engineering, 34220, Esenler, Istanbul, Turkey Received 25 December 2015; accepted 8 April 2016 Available online 30 April 2016
The performance of upflow multitube microbial fuel cell (UM2FC) from membrane concentrate of domestic wastewater (50% concentrate or a volume to concentration ratio of 2) has been investigated in a laboratory test. The test found that the UM2FC with the tin-coated copper mesh and coil spring under different hydraulic retention times (HRTs) produced maximum electricity of 916 ± 200 mW/m3 (61 mW/m2) at an HRT of 0.75 day with a 78% soluble chemical oxygen demand (sCOD) removal efficiency and 3% and 20% Coulombic efficiencies (CEs). The whole-cell resistance as calculated from the Nyquist plot and equivalent circuit were approximately 134 and 255 U for HRTs of 0.5 and 0.75 days, respectively. Considering HRT, the current increase with longer HRT could be due to longer contact time between organic material and biofilm, which results in a higher electrical efficiency. The results showed that UM2FC could represent an effective system for simultaneous membrane concentrate treatment and electricity production after further improvements on MFC and operating conditions. Ó 2016, The Society for Biotechnology, Japan. All rights reserved. [Key words: Tubular microbial fuel cell; Multielectrode connection; Electrochemical impedance spectroscopy; Surface morphology; Membrane concentrate]
Microbial fuel cells (MFCs) are microbiological systems that can be used in wastewater treatment for energy recovery and biomass reduction. The studies conducted in the last decade have focused on effective MFC design and economical electrode and separator materials. Optimizing the other operating conditions is also another important approach to improve the performance of MFCs. The MFC design, electrode performance, external operating conditions, resistance, and rate of substrate degradation principally increase the power output from MFCs (1,2). Much effort is being devoted to more effective and applicable MFC design and materials. Tubular MFC designs have attracted much attention recently to make the MFCs feasible to scale up and improve electrical performance. For example, tubular MFCs with spiral spacers were developed by creating a helical flow to increase electricity generation and investigated in both laboratory and on-site tests (3). The energy production in the tubular MFCs ranged from 0.071 to 0.073 kWh/kg chemical oxygen demand (COD), and it was proved to be an effective approach to improve energy production. In this study, an upflow multitube microbial fuel cell (UM2FC) was tested for its ability to simultaneously treat concentrate streams of domestic wastewater and produce electricity (4). The pipe-in-pipe electrode assemblies and compact design represented a new treatment technology for membrane concentrate treatment as well as electricity generation. A tubular configuration makes it possible to
* Corresponding author. Yildiz Technical University, Faculty of Civil Engineering, Department of Environmental Engineering, Davutpasa Campus, 34220 Esenler, Istanbul, Turkey. Tel.: þ90 212 383 54 02; fax: þ90 212 383 51 02. E-mail address: [email protected] (E.O. Koroglu).
achieve distribution close to optimal spatial distribution of anode, cathode, and separator in an MFC. A granular carbon anode MFC with an external cathode surrounding the vertical upflow containment tube was considered by Rabaey et al. (5). Maximum and average power densities of 90 and 52 W/m3 were obtained with acetate at an organic loading rate (OLR) of 1.1 kg COD/m3/day. A similar configuration of tubular reactor was investigated with an open-air biocathode generating 65 W/m3 of power density at an OLR of 1.5 kg COD/m3/day (6). A recent development of tubular MFCs has aimed to optimize operating conditions to increase the production of electricity and understand electrochemical behavior of cells and physical properties such as surface morphology and elemental analysis. Li et al. (7) tested the feasibility of bioelectricity production from animal carcass wastewater under different hydraulic retention times (HRTs). After a start-up period of approximately 55 days, when HRT was set at 3 days, MFC showed best bioelectricity performance with the maximum power density of 2.19 W/m3 and minimum internal resistance of 30.3 U. Increasing HRT from 3 to 6 days increased COD and nitrate removal efficiency, but reduced the rate of production of ammonia. Kim et al. (8) investigated the energy recovery using longitudinal tubular MFC reactors with influent sucrose OLRs between 0.04 and 0.42 g COD/l/day. The maximum energy production was 1.75 Wh/g COD at an OLR of 0.24 g/l/day and Coulombic efficiency (CE) ranged from 9% to 92%. Therefore, the tubular MFC design is promising for wastewater treatment and electricity generation. Nevertheless, the disposal and treatment of membrane concentrates besides wastewater is a serious problem that constrains the application of membrane technology (9). MFCs could represent
1389-1723/$ e see front matter Ó 2016, The Society for Biotechnology, Japan. All rights reserved. http://dx.doi.org/10.1016/j.jbiosc.2016.04.002
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an effective system for membrane concentrate treatment and electricity production simultaneously. The feasibility of membrane concentrate treatment and electricity production has not been considerably tested in the MFCs. Koroglu et al. (4) studied the generation of electricity from membrane concentrate using a UM2FC. In this study, different electrode materials were installed in a tubular MFC differently from Koroglu et al. (4) with the same substrate and inoculum. The objectives of this study were to (i) investigate the performance of UM2FC for electricity generation and wastewater treatment from membrane concentrate; (ii) investigate the effect of HRT; (iii) evaluate the electrochemical behavior of UM2FC and identify the distribution of the internal resistance; and (iv) investigate the surface morphology, dispersion, and functional groups by scanning electronic microscopy (SEM) and attenuated total reflectioneFourier transform infrared (ATReFTIR) spectroscopy. MATERIALS AND METHODS Reactor configuration and operation In this study, a patented (by Turkish Patent Institute with number of TR-201106609B) tubular UM2FC was used with a tin-coated mesh (LessEMF, USA) as anodeecathode electrode, stainless steel coil spring (0.5-mm wire diameter, 5-mm outer diameter, and 1.1 103-U cm1 electrical resistivity) to obtain a mechanical support between mesh electrodes, cylindrical glass reactor, and a tubular Nafion (Perma Pure) membrane. The volume of the anode chamber was 100 ml and the total surface area of the electrodes was 15 cm2. The electrodes were constructed by entwining the membrane over spring and rolling up tin-coated copper meshes around the springs (Fig. 1). Five electrode configurations were connected in parallel by a titanium wire with 100-U external resistance and their electrical responses were monitored together. Before setting up the electrode, membranes were pretreated in accordance with Koroglu et al. (4) described previously by sequential immersion in a 30% volume fraction H2O2 solution, 49.04 g L1 H2SO4 solution, and deionized water at 85 C for 1 h. During the initial start-up period, the UM2FC was inoculated with a sediment _ sample (2:10 v:v) obtained from Golden Horn in Istanbul, Turkey, and the anodic liquid was collected from the ISKI Domestic Wastewater Pretreatment Plant in Yenikapi (41 000 09.2800 N 28 560 56.8700 E). The UM2FC was operated for approximately 48 h until the desired current generation and biofilm formation were observed. The cathode chambers were recirculated continuously with oxygensaturated distilled water. The experimental setup was the same as that of Koroglu et al. (4). The reactor was operated in batch mode at room temperature (20 2 C) with raw domestic wastewater and anodic liquid was recirculated via a circulating pump to produce gentle shear on the surface of the anode to obtain an active biofilm. After 48 h of enrichment and adaptation period, the UM2FC switched to continuous mode with concentrated wastewater with an HRT of 0.75e0.5 day. The molecular weight (MW) distribution analysis and membrane concentrate production using
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membrane filtration were done as described by Koroglu et al. (4) using a stirred filtration apparatus (Amicon-8400, Merck Millipore) under 200-kPa absolute pressure for MW distribution analysis and a laboratory scale cross-flow mode filtration apparatus with a flat sheet membrane system for membrane concentrate production of domestic wastewater. The 50% retained ratio or a volume concentration ratio (VCR) of 2 was used in this study, and the former represents the percentage ratio of filtered wastewater volume to initial feed volume or VCR was used to express the degree of concentration of a target compound, as shown by the following equation: VCR ¼ CF ¼
Vp V0 ¼ 1þ Vr Vr
(1)
where V0 is the initial feed tank volume, Vp is the volume of the permeate, and Vr is the volume retained (10). The characteristics of the domestic wastewater and membrane concentrate were: pH 6.9 0.8, conductivity 900 300 mS m1, soluble chemical oxygen demand (sCOD) 480 70 g m3, and total suspended solid (TSS) 240 28 g m3 for raw wastewater and pH 7.2 0.0, conductivity 950 210 mS m1, sCOD 685 31 g m3, and TSS 348 24 g m3 for 50% concentrate stream. Measurement and analysis The electrochemical impedance spectroscopy (EIS) analysis represents the limiting factors as internal resistance in MFCs and in this study, internal resistance of UM2FC cell was segmented in various specific resistances such as Ohmic resistance (RU), anodic charge transfer resistance (Ra), cathodic charge transfer resistance (Rc), and constant phase element (CPE) as a component of equivalent electrical circuit. The impedance data of the UM2FC were analyzed by fitting them to an equivalent electrical circuit model. The magnitude of the impedance can be expressed in terms of the real and imaginary components, as given in Eq. 3: jZj ¼
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Z 2r þ Z 2j
(2)
Electrochemical measurements were monitored by a computer-based potentiostat system (Ludre L02/V01, Ludre Software, Istanbul, Turkey) every 5 min (4). EIS data were recorded on a Ludre potentiostat in a frequency range of 100 kHz to 1 MHz and amplitude of 10 mV. The impedance spectra were recorded when the maximum power was observed, because the power reaches its maximum values as a result of the maximum biochemical conversion rate. The internal resistances were calculated by fitting and simulating the experimental data with equivalent circuits using the ZsimpWin 3.22 software (11). The concentrations of sCOD and TSS were measured using the standard methods (method 5220 D and 2540 D). All samples for SCOD measurements were filtered through 0.45-mm syringe filters (polyvinylidene difluoride (PVDF), 25 mm, Restek). Measurement of pH and conductivity was made using a probe (WTW Multi 3420, Germany) after sampling. CE was calculated as given by Logan (12): CE ¼
Ms $I F$bes $q$DC
(3)
where Ms is the MW of the substrate added, I is the circuit current, F is the Faraday’s constant, bes is the number of electrons exchanged per mole of oxygen, q is the flow rate, and DC is the difference between the influent and effluent CODs.
FIG. 1. Configuration of UM2FC: (A) tin-coated copper mesh; (B) stainless steel coil springs; and (C) the assembled UM2FC for the test.
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FIG. 2. Power density and COD removal outputs as a function of time at different stages.
FTIR spectral analysis was performed to determine the changes in microstructure of Perma Pure membrane using an ATR method in IR spectrometer by a Watson 1000 FTIR apparatus at ambient temperature. The membranes were pressed against the crystal using a pressure applicator at the maximum setting. Spectra were acquired for 100 scans between 400 and 4000 cm1 at a resolution of 16 cm1. These spectra were analyzed in more detail for chemical shifts and peaks. SEM and energy dispersive X-ray spectrometry (EDX) analyses was carried out using an Apollo-300 Cam Scan scanning electron microscope to determine the morphology of membranes. The film surface was sputter-coated with gold (Polaron range). Then, elements in the membranes before and after beer water are determined by EDX.
RESULTS AND DISCUSSION Electricity generation and treatment performance The reactor configuration was similar to previous configuration and no significant change was observed; therefore, the configuration and results were compared with the previous reactor (4). The 100-U power density generation at external resistance and different HRTs was monitored in the UM2FC for 37 days (Fig. 2). It was observed that the UM2FC produced unstable electrical current
FIG. 3. Impedance spectra and equivalent circuit exploited for the fitting of the impedance spectra for the UM2FC with different operating conditions.
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TABLE 1. Fit parameters for spectra of the UM2FC at different operating conditions. HRT
Ra (U)
Rc (U)
Rs (U)
CPEa (U1sN)
CPEc (U1sN)
Rint (U)
0.5 0.75
61.93 144.9
63.16 101.2
8.84 9.13
0.01501 0.00896
0.01338 0.01107
133.93 255.23
density, mostly varying between 20 and 600 mA/m2. The power densities for different HRTs were 916 200 mW/m3 or 61 mW/ m2 (HRT 0.75 day) and 22 4 mW/m3 or 12 mW/m2 (HRT 0.5 day). The results are higher (0e260 mA/m2) than those obtained from a tubular multitube MFC (4), but much lower (2e60 W/m3) than laboratory-scale tubular MFCs (5,13). The increase of the OLR influenced direct anodic oxidation in UM2FC; hence, the power density was increased. Direct anodic oxidation might activate the oxidation species on the anode surface through bioelectrochemical reactions, which would facilitate oxidation of organic compounds in wastewater and lead to enhanced electricity production. The observed high power output can be attributed to the availability of a higher substrate concentration to sustain metabolic activity (14). There was an electrical problem in the laboratory between days 18 and 22, during which the reactor was fed manually in batch mode, leading to a decrease in UM2FC performance. Then, the operation mode was switched again to continuous mode, and steady-state conditions were obtained in 4e5 days. When the HRT was decreased to 0.5 day, a sharp decrease on the UM2FC performance was observed. Clearly, the HRT of 0.75 day for this type of reactor was beneficial for electricity generation. Considering HRT of 0.75 and 0.5 days, the current increase with longer HRT could be due to higher contact time between organic material and biofilm, and that results in higher electrical efficiency (15). The unstable current density and power density compared with Rabaey et al. (5) may be because the substrate used in this study has low organic constituent or more complex compounds such as recalcitrants. The laboratory tests generally use easily degradable
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substrates in anode, such as glucose, and that results in higher efficiencies in MFCs. The other reason might be biofouling on the membrane surface. Because of the nature and membrane concentrate of the domestic wastewater, biofilm quickly formed on the anode surface and results in membrane fouling. Over the range of HRT tests, the overall sCOD removal efficiency ranged from 40% to 78% for UM2FC (Fig. 2). The maximum sCOD removal efficiencies were 78% and 58% for HRTs of 0.75 and 0.5 days, respectively. Although the sCOD removal efficiency in UM2FC was lower than that of activated sludge systems, the UM2FC produced much less sludge. The CEs of different HRTs were found to vary between 3% and 20%. It has been reported that approximately 20% of the COD removal is practically related to electricity production (16). The maximum CE based on sCOD removal ranged from 10% to 20% at HRT of 0.75 day. The obtained CE was >0.3 0.04% for a pilot-scale multianode/cathode MFC of 16-L capacity (17) and 3 1.2% using domestic wastewater for a stackable pilot MFC of 250-L capacity at an Rext of 2 U (18). However, the results are lower than 38e49% CE for tubular MFC using sucrose wastewater with a reactor volume of 220 ml (8). This lower CE was attributed to several factors such as fermentation and complexity of the substrate. However, the domestic wastewater used in this study can be easy biodegraded. Oxygen diffusion to the anode chamber through Perma Pure membrane could possibly be another reason for the reduced energy conversion (19). The whole-cell resistances calculated from the Nyquist plot and equivalent circuit (Fig. 3) were approximately 134 and 255 U for HRTs of 0.5 and 0.75 days (Table 1). As given in Table 1, anodic and cathodic charge transfer resistances and Ohmic resistance increased, and as a result, total internal resistance decreased with the decrease of HRT from 0.75 to 0.5 day. The internal resistance at an HRT of 0.75 day was 90% higher than that at an HRT of 0.5 day. The increase of internal resistance was caused by 61.95% anodic charge transfer resistance, 28.40% cathodic charge transfer resistance, and 0.22% Ohmic resistance.
FIG. 4. SEM images of the membrane surfaces populated with bacterial cells: (A) pure membrane (1000); (B) used membrane (20,000); and (C) used membrane (5000).
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Anodic charge transfer resistance showed a 57% decrease by switching the HRT from 0.75 to 0.5 day, and this attributes majorly to the increase in internal resistance. The possible reason of increased anodic and cathodic charge transfer resistances might be the lack of electron transfer between bacteria and electrode and hence a decrease in chemical reaction in anode and cathode. Thus, the major factor in the increase of the total internal resistance could be related to a decrease in chemical reaction occurring in anode. SEM and EDX analyses Analysis of SEM images provided more detailed information about the conditions of the pure and used membrane surfaces (20,21). Fig. 4 shows the SEM images of pure and used membranes surfaces. The pure membranes had a uniform surface morphology, and no cracks and pores were observed. As shown in Fig. 4, the microbial community is attached to the membrane surfaces with a uniform morphology and different cations are formed on the surface of membranes used by the UM2FC. The results of EDX analysis for pure and used membranes are shown in Fig. 5. The EDX analysis showed the presence of some inorganic salt precipitations on the used membranes. Fig. 5 shows the composition of particles on the membrane surface. Chemical analysis of the top layer of pure membrane film
by EDX analysis shows that the surface contains carbon (C) and fluorine (F). The different elements present on the surface of used membranes are carbon (C), oxygen (O), fluorine (F), calcium (Ca), copper (Cu), and silicon (Si). It can be seen that these elements are evenly distributed on the membrane surface. These observations can be explained by the biofilms on the membrane surfaces. SEM and EDX analyses revealed that fouling of the membrane surface was attributed to the presence of bacteria in cation and anion, microorganisms from fungi mixture, extracellular microbial polymers, and the inorganic salt (21,22). The formed biofilms constitute a physical barrier against protons from the anode side to the cathode side during the pass of protons. During the formation of biofilm, the electrical resistance and pH gradient of the MFC are increased, which resulted in a loss of performance (23,24). SEM, EDX, and ATReFTIR analyses revealed that fouling on the anode surface was explained with the decrease in migration of protons (24,25). FTIR analysis Infrared spectra of both anode and cathode sides of the membrane are shown in Fig. 6 as pure and used. Water is present in the structure of membranes in both free and connected forms. The free water was usually located in the region between 3700 and 3080 cm1 (Fig. 6) and presented as monomeric H2O molecules. However, the bound water was found
FIG. 5. EDX spectra of membranes used in UM2FC: (A) pure membrane and (B) used membrane.
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FIG. 6. ATReFTIR spectra of membranes.
in the porous structure and it was difficult to remove (22,26,27). This band hydrophilicity and conductivity of membrane were attributed to the increase of HeO stretching in the free SO3H group (28). In Fig. 6, the S]O (1410 cm1) and SeOH (910 cm1) stretching bands of the eSO3H group are observed. AmideI band as an indicator of proteins were located in the region between 1600 ile 1650 cm1 which was not seen this band (20). It is evident from the figure that the membranes were observed at 1300 and 1056 cm1 due to asymmetric and symmetric SO 3 stretching. Although the strong CeF stretching bands were shrouded, the presence of SO 3 stretching bands and humidity sensing can be evidenced with the transfer of proton (29). This group of bands can provide information about proton transfer, proton transport, and the mechanism involved. The strong bands centered at 1300 and 1100 cm1 were attributed to CF stretching band (30). Furthermore, it is observed as attributed to the CeOeC linkage between the backbone and side chain (Fig. 6) (30). The ATReFTIR spectra of the anode and cathode surface of the used membrane are compared in Fig. 6. A shift to low frequency and a decrease in intensity of the OH stretching band on anode and only a shift to low frequency on cathode surface compared with pure membrane were determined. In a fuel cell system, it is well known that this type of decrease of intensity of the OH stretching band is directly proportional to the decrease in membrane conductivity and OH groups (28,31). The shifting of bands can be shown as a result of microbial contamination (31). The magnitudes of shifting in anode and cathode were determined to be 54 and 173 cm1. A remarkable decrease of the peak magnitude was observed at 2950 cm1 in anode compared with cathode. The magnitudes of the asymmetrical and symmetrical eSO 3 stretching bands were decreased in anode and disappeared and shifted to a low frequency (1029 cm1) in cathode. A new peak was observed in anode at 855 cm1, which was attributed to a biofilm layer on membrane surface. The results showed that biofilm layer was organic-based and the structure of the layer contained carbon (C), oxygen (O), sulfide (S), thiol (SeH) and disulfide (SeS). In this study, tin-coated copper mesh and coil spring made from stainless steel were tested as electrode materials in UM2FC design. These materials showed satisfactory results, but unstable electricity production comparable to a previous study. It is concluded that utilization of MFC with mesh and spring significantly reduces the internal resistance. Results obtained from the system were among the higher values reported earlier. The design also provided a sustainable solution to membrane concentrate treatment over 70% COD removal. However, its efficacy should be further studied.
ACKNOWLEDGMENTS The authors gratefully acknowledge the Scientific and Technological Research Council of Turkey (TUBITAK) (Project No. 111Y252) for financial support and Istanbul Water and Sewage Administration (ISKI) for providing wastewater. They also thank Dr. Cenk Denktas and Dr. Derya Yılmaz Baysoy for their valuable comments.
References 1. Zhou, M., Chi, M., Luo, J., He, H., and Jin, T.: An overview of electrode materials in microbial fuel cells, J. Power Source, 196, 4427e4435 (2011). 2. Liu, H., Cheng, S., and Logan, B. E.: Power generation in fed-batch microbial fuel cells as a function of ionic strength, temperature, and reactor configuration, Environ. Sci. Technol., 39, 5488e5493 (2005). 3. Zhang, F., Ge, Z., Grimaud, J., Hurst, J., and He, Z.: Improving electricity production in tubular microbial fuel cells through optimizing the anolyte flow with spiral spacers, Bioresour. Technol., 134, 251e256 (2013). 4. Koroglu, E. O., Baysoy, D. Y., Cetinkaya, A. Y., Ozkaya, B., and Cakmakcı, M.: Novel design of a multitube microbial fuel cell (UM2FC) for energy recovery and treatment of membrane concentrates, Biomass Bioenergy, 69, 58e65 (2014). 5. Rabaey, K., Lissens, G., and Verstraete, W.: Microbial fuel cells: performances and perspectives. Biofuels for fuel cells: renewable energy from biomass fermentation, pp. 377e399. IWA Publishing, London (2005). 6. Clauwaert, P., Van der Ha, D., Boon, N., Verbeken, K., Verhaege, M., Rabaey, K., and Verstraete, W.: Open air biocathode enables effective electricity generation with microbial fuel cells, Environ. Sci. Technol., 41, 7564e7569 (2007). 7. Li, X., Zhu, N., Wanga, Y., Li, P., Wua, P., and Wua, J.: Animal carcass wastewater treatment and bioelectricity generation in up-flow tubular microbial fuel cells: effects of HRT and non-precious metallic catalyst, Bioresour. Technol., 128, 454e460 (2013). 8. Kim, J. R., Premier, G. C., Hawkes, F. R., Rodríguez, J., Dinsdale, R. M., and Guwyb, A.: Modular tubular microbial fuel cells for energy recovery during sucrose wastewater treatment at low organic loading rate, Bioresour. Technol., 101, 1190e1198 (2010). 9. Sperlich, A., Warschke, D., Wegmann, C., Ernst, M., and Jekel, M.: Treatment of membrane concentrates: phosphate removal and reduction of scaling potential, Water Sci. Technol., 61, 301e306 (2010). 10. Wang, L. K., Chen, J. P., Hung, Y. T., and Shammas, N. K.: Membrane and desalination technologies, pp. 433e476. Springer, New York (2011). 11. Cheng, K., He, D., Peng, T., Lu, H., Pan, M., and Mu, S.: Porous grapheme supported Pt catalysts for proton exchange membrane fuel cells, Electrochim. Acta, 132, 356e363 (2014). 12. Logan, B. E.: Microbial fuel cell, 1st ed. John Wiley & Sons Inc., Hoboken (2008). 13. Zhang, F., Jacobson, K. S., Torres, P., and He, Z.: Effects of anolyte recirculation rates and catholytes on electricity generation in a liter-scale upflow microbial fuel cell, Energy Environ. Sci., 3, 1347e1352 (2010). 14. Mohan, S. V., Raghavulu, S. V., Peri, D., and Sarma, P. N.: Integrated function of microbial fuel cell (MFC) as bioelectrochemical treatment system associated with bioelectricity generation under higher substrate load, Biosens. Bioelectron., 24, 2021e2027 (2009).
600
KOROGLU ET AL.
15. Sharma, Y. and Li, B.: Optimizing energy harvest in wastewater treatment by combining anaerobic hydrogen producing biofermentor (HPB) and microbial fuel cell (MFC), Int. J. Hydrog. Energy, 35, 3789e3797 (2010). 16. He, Z. and Mansfeld, F.: Exploring the use of electrochemical impedance spectroscopy (EIS) in microbial fuel cell studies, Energy Environ. Sci., 2, 215e219 (2009). 17. Jiang, D., Curtis, M., Troop, E., Scheible, K., McGrath, J., Hu, B., Suib, S., Raymond, D., and Li, B.: Pilot-scale study on utilizing multi-anode/cathode microbial fuel cells (MAC MFCs) to enhance the power production in wastewater treatment, Int. J. Hydrog. Energy, 36, 876e884 (2011). 18. Feng, Y., He, W., Liu, J., Wang, X., Qu, Y., and Ren, N.: A horizontal plug flow and stackable pilot microbial fuel cell for municipal wastewater treatment, Bioresour. Technol., 156, 132e138 (2014). 19. Nandy, A., Kumar, V., Mondal, S., Dutta, K., Salah, M., and Kundu, P.: Performance evaluation of microbial fuel cells: effect of varying electrode configuration and presence of a membrane electrode assembly, New Biotechnol., 32, 272e281 (2015). 20. Rabiller-Baudry, M., Gouttefangeas, F., Le Lannic, J., and Rabiller, P.: Coupling of SEM-EDX and FTIR-ATR to (quantitatively) investigate organic fouling on porous organic composite membranes, pp. 1066e1076, in: MéndezVilas, A. (Ed.), Current microscopy contributions to advances in science and technology. Formatex, Badajoz (2012). 21. Ping, Q., Cohen, B., Dosoretz, C., and He, Z.: Long-term investigation of fouling of cation and anion exchange membranes in microbial desalination cells, Desalination, 325, 48e55 (2013). 22. Xu, J., Sheng, G. P., Luo, H., Li, W., Wang, L., and Yu, H.: Fouling of proton exchange membrane (PEM) deteriorates the performance of microbial fuel cell, Water Res., 46, 1817e1824 (2012). 23. Leong, J. X., Dauda, W. R., Ghasemi, M., Liew, K. B., and Ismail, M.: Ion exchange membranes as separators in microbial fuel cells for bioenergy
J. BIOSCI. BIOENG.,
24.
25.
26.
27.
28.
29.
30.
31.
conversion: a comprehensive review, Renew. Sustain. Energy Rev., 28, 575e587 (2013). Chung, K., Fujiki, I., and Okabe, S.: Effect of formation of biofilms and chemical scale on the cathode electrode on the performance of a continuous two-chamber microbial fuel cell, Bioresour. Technol., 102, 355e360 (2011). Chae, K. J., Choi, M., Ajayi, G. F., Park, W., Chang, I. S., and Kim, I. S.: Mass transport through a proton exchange membrane (Nafion) in microbial fuel cells, Energy Fuel, 22, 169e176 (2008). Noto, V. D., Piga, M., Giffin, S., Lavina, E. S., Smotkin, J. Y., and Sanchez, C.: Influence of anions on proton-conducting membranes based on neutralized nafion 117, triethylammonium methanesulfonate, and triethylammonium perfluorobutanesulfonate, J. Phys. Chem., 116, 1361e1369 (2012). Belfer, S., Fainchtain, R., Purinson, Y., and Kedem, O.: Surface characterization by FTIR-ATR spectroscopy of polyethersulfone membranes-unmodified, modified and protein fouled, J. Membr. Sci., 172, 113e124 (2000). Ghasemi, M., Daud, W. R., Ismail, M., Rahimnejad, M., Ismail, A., Leong, J., Miskan, M., and Liew, K.: Effect of pre-treatment and biofouling of proton exchange membrane on microbial fuel cell performance, Int. J. Hydrog. Energy, 38, 5480e5484 (2013). Wu, R., Sun, Y., Lin, C., Chen, H., and Chavali, M.: Composite of TiO2 nanowires and nafion as humidity sensor material, Sens. Actuators, 115, 198e204 (2006). Danilczuk, M., Lin, S., Schlick, S., and Hamrock, M.: Understanding the fingerprint region in the infra-red spectra of perfluorinated ionomer membranes and corresponding model compounds: experiments and theoretical calculations, J. Power Source, 196, 8216e8224 (2011). Barbora, L., Singhb, R., Shrotib, N., and Verma, A.: Synthesis and characterization of neodymium oxide modified nafion membrane for direct alcohol fuel cells, Mater. Chem. Phys., 122, 211e216 (2010).