International Journal of Energy Science (IJES) Volume 4 Issue 1, February 2014 doi: 10.14355/ijes.2014.0401.07
Microbial Fuel Cells for Energy Recovery from Waste Emre Oğuz Köroğlu*1, Bestamin Özkaya2, Afşin Yusuf Çetinkaya3 Department of Environmental Engineering, Yıldız Technical University Istanbul, Turkey *email@example.com; firstname.lastname@example.org; 3afsincetinkaya @gmail.com Abstract Microbial fuel cells (MFCs) are bioelectrochemical systems which enable the conversion of chemical energy directly into electrical energy with microorganism. Studies focused on using organic materials of waste to increase power production performance. In this study, two different MFC reactors were investigated to produce electricity using domestic wastewater. The highest current and power density were 1385 mA/m2 and 16 mW/m2 at Ti-TiO2/Nafion combination with 78% COD removal. Ti-TiO2/CMI7000 assemblies generated 750 mA/m2 of current densities and 5 mW/m2 of power density and HRT of 1 day was found favorable for MFC system.
PEM, electrons transfer to anode electrode by bacteria and transport cathode electrode via the external circuit (Logan, 2008).
Keywords Microbial Fuel Cell; Membrane; Wastewater
Introduction Increase in the use of fossil fuels to meet energy needs has accelerated environmental problems and the need of renewable energy has increased steadily (Sung et al., 2010); making the focus of researches shift to alternative energy sources to replace fossil fuels. Mankind has been in a constant quest to meet this need. This quest has found new energy sources as time goes by. One of these new energy sources is Microbial Fuel Cell (MFC). Microbial fuel cells holds an important place among the bio-electrochemical systems. In microbial fuel cells, by means of metabolic activities of microorganisms biomass is converted into electrical energy systems (Du et al., 2007). It uses wastewater as a nutrient use in electricity production and treats wastewater during the electricity production, so in terms of both cost and benefits, microbial fuel cells have attracted much attention. MFC typically consists of an anode chamber, cathode chamber and proton exchange membrane (PEM) which separates anode and cathode chambers (Fig. 1). Microorganisms oxidize organic matters in the anode chamber and produce electrons and protons (Liu et al., 2010). Protons diffuse into cathode chamber through
FIG. 1 SCHEMATIC VIEW OF MICROBIAL FUEL CELL
A list of various wastewaters used in microbial fuel cell and obtained power generations is given in Table 1 TABLE 1 LIST OF WASTEWATER USED AS SUBSTRATE IN MFC STUDIES
MFC Type Power Generation References Single chamber 261 mW/m2 Min et al. Swine Two chamber 45 mW/m2 Starch Air-cathode 239,4 mW/m2 Lu et al. Domestic Two chamber 190 mW/m2 Oh et al. Domestic Baffled 60 W/m3 Oh et al. Domestic Air-cathode 422 mW/m2 Ahn et al. Air-cathode 205 mW/m2 Feng et al. Beer Brewery Single chamber 170 mW/m2 Leachate Two chamber 2060,19 mW/m3 You et al. Leachate Single chamber 6817,4 mW/m3 Galvez et al. Leachate Colon type 1822 μW/cm2 Galvez et al. Leachate Air-cathode 344 mW/m3 Puig et al.
In this study, in order to develop high efficiency MFCs, different membrane configurations were tested and electricity generation from different hydraulic retention time (HRT) was investigated. Materials and Methods MFC Construction In this study, two-chamber microbial fuel cell was
International Journal of Energy Science (IJES) Volume 4 Issue 1, February 2014
used with a volume of 275 ml and made of plexiglass (Ozkaya et al., 2013). Schematic view of two-chamber MFC is given Fig. 2. Partitions separated by Nafion® 117 and CMI7000 PEM membranes and cathode compartment were filled with distilled water and aerated.
times to evaluate electricity generation capacity of reactors (Fig. 3). HRT was decreased stepwise from 2 d to 1.5 d, 1 d, 0.75 and 0.5 d, respectively. MFCs were fed with domestic wastewater taken from Yenikapı Pre-treatment Plant and characterization is given in Table 1. Calculations and Measurements Voltage across the external resistance of Ω 10 was measured at 5 min intervals using a data logger system connected to a computer. Power and current were calculated as described in Logan et al, 2008.
FIG. 2 TWO CHAMBER MFC
Nafion 117 was pretreated at 85oC in 5% H2O2, distilled water, 0.05 M H2SO4 and distilled water, respectively. CMI7000 was pretreated at 40oC in 5% NaCl for 24 hours. Two-chamber MFC was usually maintained under strict anaerobic condition. Ti-TiO2 electodes were used as anode and cathode electrode with 7 cm2 of surface area. ®
Results Obtained current and power densities with Ti-TiO2 electode configurations with Nafion® 117 and CMI7000 are shown in Fig. 4.
Inoculation and Operation The described reactor was constructed, inoculated with sediment sample taken from Golden Horn in Istanbul and operated as a fed-batch MFC reactor for about 45 days. Temperature was set at 25◦C during inoculation and operation. In case of the lowertemperature, anode compartments were heated by a water-bath. CODs were measured using standard methods (APHA, 1998).
FIG. 4 TIME DEPENDENT CURRENT AND POWER DENSITY (A: CMI7000; B:Nafion)
FIG. 3 HRT AND ORGANIC LOADING RATE TABLE 2 WASTEWATER CHARACTERIZATION
Concentration 477 ± 69.9
208 ± 33.5
28 ± 6.9
9.005 ± 3.096
6.9 ± 0.8
6 ± 1.2
MFC reactors operated at different hydraulic retention
According to the results of the study, Ti-TiO2/CMI7000 pair of electrode-membrane reactor started to produce electricity after 2 days. Power increased by reducing the hydraulic retention time and reached maximum on HRT for 1 day. Maximum current and power densities obtained in 1 day were 750 mA/m2 and 5 mW/m2, respectively. COD removal efficiency was measured 63%. A decline in electricity production has been seen due to reduction of HRT to 0.5 day so HRT was set to be 1 day and continued under this conditions. Ti-TiO2/Nafion pair of electrode-membrane reactor has been activated as late as 8 days but power generation observed more than CMI7000. The maximum current and power density were 1385 mA/m2 and 16 mW/m2 29
International Journal of Energy Science (IJES) Volume 4 Issue 1, February 2014
with 78% COD removal. Increasing electricity production as reduction of HRT to 0.75 day was affected by decreasing HRT to 0.5 day. Therefore, HRT was set to be 1 day again at 35th day and continued to operation.
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bacterium sp. Strain MFCO3 under Alkaline Condition
The results showed that two-chambered MFC was able to generate electricity and simultaneously treat domestic wastewaters. MFCs was performed during operation as illustrated by variations in HRT. The results showed that HRT and membrane material play an important role in electricity generation performance in the fed-batch MFC. The MFCs performed better at a HRT of 1 day and with Nafion 117 PEM membrane. Nevertheless, it remains a challenge to clear the applicability of MFC as a direct step waste to electricity technology so further investigations are needed to scale MFC up and integrate into wastewater treatment plants.
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Electrode Surface Areas as Factors that Affect Power
The authors gracefully acknowledge the financial support from TÜBİTAK with project number of 111Y252 and Yildiz Technical University.
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