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  • International Journal of Advanced Research in Engineering RESEARCH IN ENGINEERING INTERNATIONAL JOURNAL OF ADVANCED and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME AND TECHNOLOGY (IJARET) ISSN 0976 - 6480 (Print) ISSN 0976 - 6499 (Online) Volume 4, Issue 7, November - December 2013, pp. 198-206 © IAEME: www.iaeme.com/ijaret.asp Journal Impact Factor (2013): 5.8376 (Calculated by GISI) www.jifactor.com IJARET ©IAEME EFFECT OF COD ON OCV, POWER PRODUCTION AND COULOMBIC EFFICIENCY OF SINGLE-CHAMBERED MICROBIAL FUEL CELLS T. Opoku-Donkor, R. Y. Tamakloe, R. K. Nkum, K. Singh Department of Physics, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana (West Africa) ABSTRACT An attempt has been made to find the effect of Chemical Oxygen Demand (COD) on the Open Circuit Voltage (OCV), Power production and Coulombic efficiency of single – chambered Microbial Fuel Cells (MFCs). Three different MFCs of similar design have been fabricated using carbon paper doped with platinum as cathode and graphite as anode separated by Proton Exchange Membrane (PEM).It has been found that the Open Circuit Voltage (OCV), power production and Coulombic efficiency obtained are in direct proportion with COD level. Keywords: MFC = Microbial Fuel Cell; SC-MFC = Single Chambered MFC; Ecell = Total Cell Potential; OCV = Open Circuit Voltage GGBL = Guinness Ghana Brewery Limited INTRODUCTION Power generation from MFCs using anaerobic microbes is a novel technology with great potential for alternative energy generation and environmental pollution reduction. Microbial fuel cell is a system that drives a current to generate electricity using bacteria found in nature. Organic substances are degraded by micro-organisms through anaerobic metabolism liberating electrons and protons in a biochemical cell using anode and cathode separated by proton exchange membrane (PEM). For example, nutrient such as glucose is broken down into carbon dioxide, hydrogen ions and electrons. C12H22O11 + 13H2O -> 12CO2 + 48H+ +48e- 198
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME The current is generated through the flow of electrons via a complete electric circuit. In 1910, Potter had proposed the idea of production of EMF during fermentation of organic compounds by yeast. However the first known patent of MFC was in 1967. Since then, different researchers worked on the development of MFCs with different setups. For example, dual chambered cell with a proton exchange membrane or single chambered cell with anode and cathode separated by cotton cloth, were successful [1]. There are two main components of the fuel cell; cathode and anode compartments along with a cation specific membrane. In the anode compartment, microorganism oxidizes substrates which generate electrons and protons. Electrons are then transferred to the cathode compartment via an external electric circuit. Protons are transferred to the cathode compartment through the cation specific membrane. Consumption of electrons and protons in the cathode compartment with oxygen results in formation of water. As stated by Logan et al [2] virtually any biodegradable organic matter can be used in an MFC, including volatile acids, carbohydrates, proteins, alcohols, and even relatively recalcitrant materials like cellulose. A large amount of beer brewery wastewater is produced from cooling (eg. saccharification cooling, fermentation) and washing units in brewery industry and often causes several environmental problems. The wastewater is non-toxic, but has high Biological Oxygen Demand (BOD) compared with other industrial wastewater. Generally, biological methods used for the beer brewery wastewater treatment are reported to perform well in COD removal [3]. Domestic wastewater is also reported in electricity generation in several MFC configurations (Liu et al. 2004; Liu & Logan 2004; Min & Logan 2004) [4]. Beer brewery wastewater might be good source for electricity generation in MFCs due to its nature of high carbohydrate and low ammonium-nitrogen concentration. In this study, we have successfully verified the potential of brewery wastewater (Malta Guinness - brewed from barley, hops, and water) to be used as fuel to generate electricity in a singlechamber MFCs. All the experiments have been performed at temperature between 25 oC and 26 oC. The scope of this study comprises two aspects: (i) to examine the possibility of direct power generation from brewery wastewater; (ii) to investigate effect of different loading of COD on OCV and Coulombic efficiency (CE). Besides, the main purpose of the study was also to validate workability of a novel MFC design in terms of current generation and cheap materials, hence showing current generation could be increased with multiple anodes sharing a common cathode and also providing possibility for serial connectivity for increasing voltage output. COULOMBIC AND ENERGY EFFICIENCY OF MFC The generation of power is a main goal of MFC operation, but there is a need to extract as much of the electrons stored in the biomass as possible as current, and to recover as much energy as possible from the system. The recovery of electrons is defined as the fraction (or percent) of electrons recovered as current versus that in the starting organic matter and referred as Coulombic efficiency(CE) [5]. CE = Coulombs recovered/Total coulombs in the substrate The energy eficiency of an MFC is based on energy recovered in the system compared to the energy content of the starting material. The energy efficiency, ηMFC, is the ratio of power produced by the cell over a time interval ‘t’ divided by the heat of combustion of the organic substrate, or ηMFC = ∫ EMFC I dt / H ns where H is the heat of combustion n (J mol-1) and n, is the amount (mol) of substrate added. 199
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME POWER PRODUCTION BY MFC From the graph, we read off a peak power in mW/cm2. Converting this to just power production from the system as given below P = PAN AAN Where PAN is the peak power in mW/cm2 and AAN is the area of PEM. EXPERIMENTAL PROCEDURES Preparation of PEM: Nafion 117 of area 12.6 cm2 was taken through the normal cleaning process [distilled water → 3% hydrogen peroxide → dilute sulfuric acid → distilled water ]. Fabrication of MFCs: Figures 1 – 6 show the necessary steps for the fabrication of MFCs. - 2 Perspex slabs were cut, shaped and dilled for each cell (Fig 1). - Carbon paper doped with platinum was cut and shaped (Fig 2). - PEM (Nafion 117 – Fig 3) - Cupper conductor was cut and shaped (Fig 4). - Graphite electrode (Fig 5) - A plastic container of 2 liters capacity served as the anodic chamber (Fig 6). The anode chamber contains the wastewater and the graphite electrode. The carbon paper tightens onto the PEM served as the cathode. Types of Wastewater for MFCs: Following three types of wastewater of different COD and pH from GGBL (Kumasi, Ghana) were used as Fuel for these cells. The characteristics of the wastewater are listed in Table 1: Wastewater Influent Anaerobic Balance Table 1 COD[mg/L] 3790.0 748.0 4330.0 Fig 1: Perspex slabs pH 11.18 6.80 6.01 Fig 2: Carbon paper 200
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME Fig 3: Nafion 117 Fig 4: Cupper plate and wire Fig 5: Graphite electrode Fig 6: b) Finished cell Fig 6: a) Block diagram of finished cell 201
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME Fig 7: Operational Cells setup with Campbell Scientific Ltd Datalogger CR10X, Logger to PC adapter, USB to RS232 Cable and 12 V Battery to power the logger. The Datalogger stores data every minute. We programmed the logger using Shortcut (CS PC200W 4.1 Datalogger Support Software –CR10X) Operation The cells were kept at 25 oC (+- 0.5 oC). The anode was immersed in the wastewater such that the cupper conductor did not touch the water in order to avoid corrosion. The anode chamber was sealed to maintain anaerobic system throughout the experiment. OCV readings were taken for 35 days with the CR10X datalogger which stores the differential voltage every one minute. A multimeter (Peak Tech 2010DMM) was used in the reading of the load voltage and the current through a resistance box ranging from 0 to 10,000 ohms. RESULTS AND DISCUSSION The experiment was operational for 35 days. A constant increment of OCV was observed from day one of the operation of MFCs until it got to their peak values of OCV. These values were maintained for about 10 days. The graph of OCV against time is shown in Fig 8. Also their pH and COD values at the end experiment are given in Table 2. The experiments were performed with the wastewater as collected in order to check the viability of the cells without adding inoculants and other chemicals. Wastewater Influent Anaerobic Balance Starting COD 3790.0 748.0 4330.0 Table 2 Ending COD 133 59 267 202 Starting pH 11.18 6.8 6.01 Ending pH 8.3 8.9 8.6
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME Fig 8: Open circuit voltage (OCV) as a function of time as measured (stored every munite) by the Datalogger. The lines shown are actual measured throughout the experimental period The red line indicated that the Balance produced very high voltage for a long period and thus maintains that for the period compare to Anaerobic and Influent substrates. This may be attributed to the high value of COD. The effect of external load on the voltage is shown in Fig 9. This characteristic curves show wide variation in the three substrates indicating the dominance of Balance type of wastewater. As expected, the power generation was observed to be highest when the COD was higher and the pH skews towards acidity. Using the potential drop as function of load we calculated the current density in mA/cm2 and the power. The polarization curve is shown in Fig 10. According to Logan [5] the determination of power produced varied depending on the relative sizes of the anode, cathode and PEM. We therefore, chose to normalize the current density by the PEM surface area. To obtain a polarization curve we used a series of different resistances from 0 to 10,000 on the circuit, measuring the voltage at each resistance, as shown in Fig. 9 and 10. INTERNAL RESISTANCE According to Logan [5] the maximum power occurs when the internal and external resistances are equal. From the graph shown in Fig. 11 the peak occurred at (8.04, 31.01) and this corresponds to an external resistance of 3,000 . Consequently the internal resistance for Balance is equal to 3,000 in the anode system (6 cm separation between anode and PEM). The peak for Influent occurred at 8,000 and that for Anaerobic occurred at 10,000 . The high values of the internal resistances may be due to the fact that the conductivities of the substrates were not tempered with. 203
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME Fig 9: This depicts the potential dropped verses load (external resistance). We obtained a data set as a function of resistance for the three systems Fig 10: Polarization Curves for the Three Cells 204
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME Fig 11: Power Density Curves Power Production by MFC From Fig. 11 we read off a peak power of 31.01 mW/cm2. Converting this to power production from the system we obtain P = 31.01 (mW/cm2) x (12.6 cm2) = 30 x 10-4 W Coulombic Efficiency (CE) The recovery of electrons is referred to as Coulombic efficiency, defined as the fraction (or percent) of electrons recovered as current versus that in the starting organic matter [6]. That is Where tb = Total cycle (s) I = Current (A) F = Faraday’s constant (C/mole) VAn = volume of liquid in the anode compartment (L) ∆COD = Change in COD (g/L) CE = 11.3 % Partition Surface Area of PEM per Volume = 0.7 m2/m3 205
  • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME CONCLUSION It has been found that the Balance wastewater produced power most significantly than the other two. It has been observed that the current generation of the cells increased for a higher COD and lower pH. Characterization curves for Influent and Anaerobic wastewaters are insignificant compared to that of Balance wastewater. The removal of COD of observed to be highest for the cell which produces higher current. The COD for Balance dropped from 4386 to 267mg/L for the 36 days of running. Summary of other Generated Parameters Substrate Balance Influent Anaerobic Max. OCV (mV) Max Current (mA) 782 345 66 Power Density (mW/cm2) 246 37.9 10.7 0.330 0.021 0.003 Current Density (mA/cm2) 8.04 0.34 0.028 Internal Resistance ( ) 3k 8k 10 k ACKNOWLEDGEMENTS Authors would like to thank Dr. Young-Gi Yoo of Korea Institute of Energy Research for providing Carbon paper doped with platinum. We would also like to thank the Head of Physics Department, KNUST and Guinness Ghana Brewery Limited for necessary facilities for this work. REFERENCES [1] [2] [3] [4] [5] [6] Banik et al, 2012 Greener Journal of Biological Sciences ISSN: 2276-7762 Vol. 2 (2), pp. 013-019, October 2012. Logan, B.E. 2008, Microbial Fuel Cells pp. 6. X. Wang; Y. J. Feng, H. Lee 2008, Electricity production from beer brewery wastewater using single chamber microbial fuel cell – Water Science & Technology – WST, 57.7, 1117. Liu, H., Cheng S. and Logan, B.E. 2005b, Production of Electricity from acetate or butyrate in a single chamber microbial fuel cell, Environ. Sci. Techno, 39(2), 658 -662. Logan, B.E. 2008, Microbial Fuel Cells, pp 46 – 48. Chonde Sonal G, Mishra A. S. and Raut P.D., “Bioelectricity Production from Wastewater using Microbial Fuel Cell (MFC)”, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 4, Issue 6, 2013, pp. 62 - 69, ISSN Print: 0976-6480, ISSN Online: 0976-6499. 206