| Summary: | 博士 === 國立中正大學 === 分子生物研究所 === 99 === The Microbial Fuel Cell (MFC) is a new technology, in which microorganisms produce electricity from a renewable energy source in the form of biomass. MFCs are receiving increasing scientific and more recently commercial attention as their potential for alternative energy production, wastewater treatment and bioremediation of contaminated environments is steadily realized. In MFCs, bacteria convert chemical energy to electrical energy via the catalytic breakdown of organic substrates. The electrons are then transferred to a terminal electron acceptor (TEA- oxygen, nitrate, and sulfate) which is reduced by the electrons. As an emerging technology, MFCs shows great potential for the simultaneous generation of electricity and the treatment of wastewater.
However, this thesis aims to study the development of microbial fuel cell with emphasis on different bacterial cultures and utilization of different wastewater as a carbon/food source in MFC. To achieve this aim, different experiments has been conducted. Initial study deals with the establishment of double chamber MFC with Bacillus subtilis as a model organism. The Gram-positive aerobic bacterium B. subtilis has for the first time been employed in a double chambered MFC. A glucose-fed MFC with M9 minimal medium in the anode chamber was operated for 3 months. Despite its aerobic growth pattern, sustainable electricity generation was achieved with a maximum current of 0.4 mA. The simultaneous production of electricity while utilizing complex substrate, i.e. glycerol was examined for a continuous period of around 26 days. Results suggests that glycerol, a byproduct of transesterification process, can be used as a suitable carbon source for electricity generation in MFC. Maximum current generation of 0.5 mA was primarily attributed to the consumption of glycerol by the bacteria attached to the anode. While, B. subtilis achieved highest glycerol degradation efficiency at neutral pH of 7. Due to the aerobic growth physiology of B. subtilis, we developed a MFC in which microorganisms at the cathode performed a nitrate reduction by using electrons supplied by microorganisms oxidizing glucose at the anode. Electricity generation with simultaneous nitrate reduction in a single-chamber MFC without air cathode was studied, using glucose (1 mM) as the carbon source and nitrate (1 mM) as the final electron acceptor employed by Bacillus subtilis under anaerobic conditions. A power density of 0.0019 mW/cm2 was achieved at an Rext of 220 . Nitrate as the terminal electron acceptor was found to be successfully achieved in the single chamber MFC without utilization of oxygen. This results demonstrated that high-efficiency electricity generation is possible from wastewater containing nitrate, and this represents an alternative technology for the cost-effective and environmentally benign treatment of wastewater.
Enterobacter cloacae, hydrogen gas producing bacterium was also evaluated to study the performance of double chamber MFC in to variations in anodic pH microenvironment based on current generation, maximum power density, electrochemical losses, internal resistance, electrochemical activity, COD removal, and coulombic efficiency. Considering pH as an important parameter for microbial growth and physiology to produce electrons in MFC, community wastewater as a substrate was utilized by adjusting the pH between 6.5 and 9.5. Polarization and power curves obtained with respect to individual pH, deduced the maximum current, power density, internal resistance and electrochemical losses. Maximum power density obtained from the polarization curve was observed of 0.0042 mW/cm2 for pH 7.4. The excellent performance of MFC at pH 7.4 and 6.5 indicates the efficacy of higher dehydrogenase activity of E. cloacae to served effectively at near neutral pHs. However, these results demonstrate the influence of acidic to alkaline wastewater on the current generation and wastewater treatment by E. cloacae.
Shewanella oneidensis as a most electroactive bacterium to harvest electron from different substrates was selected to utilize in the MFC. We demonstrated electricity production by agriculture (AWW), wastewater, domestic wastewater (DWW), paper wastewater (PWW) and food/dairy (FDWW) wastewater. Current generation were evaluated and compared in combination with three inoculums: wastewater endogenous microbes (MFC1), S. oneidensis (MR-1) (MFC2), and wastewater endogenous microbes with MR-1 (MFC3) in a single chamber microbial fuel cell (MFC). All the inoculums studied, varied differently to produce current output with and without the presence of S. oneidensis.
Overall results depicts the feasibility of utilizing different substrates i.e., organic substrate like glucose and wastewaters and myriads of bacteria to generate electricity in MFC.
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