Studies On The Biocathode Microbial Fuel Cell Using Two Kind Of Cathodic Electron Acceptors

As an emerging technology, microbial fuel cell (MFC) can extract electricity from wastewater and has attracted much attention during the past couple years. While a plethora of recent studies reported electricity could be generated from MFCs using various easily degradable organics as fuels in the anode, the cost of cathode materials incorporating precious metals such as Pt is prohibitive to wide-scale implementation, and the unsustainable use of ferricyanide as a catalyst-independent cathode electrolyte is not an option despite its positive effect on power density. Microbial cathode, which uses bacteria as biocatalysts to accept electrons from the cathode substratum, provides a different path that avoids the use of noble or non-noble catalysts for oxygen reduction, thereby enhancing the economic viability and environmentally sustainability of MFC systems. In this thesis, Cr (VI) and pentachlorophenol (PCP) were used as two new electron accptors in the biocathode MFCs. Kinetic parameters such as Cr(VI) reduction, PCP degradation, power generation, and effects of electrode material, poised potential, pH and temperature were assessed.Graphite fibers, graphite felt and graphite granules were evaluated as biocatalytic cathode materials in tubular MFCs in terms of Cr (VI) reduction and electricity generation. At cathode to anode surface area ratio (C/A) of 3, graphite fiber was found superior to graphite felt or graphite granule. Under a temperature of 22℃and pH 7.0, Cr (VI) reduction followed pseudo-first-order kinetic model with the rate constant being 0.451±0.003 h-1. In comparison with pH 7.0, an acidic pH of 5.0 improved Cr (VI) reduction of 27.3% and power generation of 61.8% whereas an alkaline pH of 8.0 decreased Cr (VI) reduction of 21.2% and power generation of 6.0%. Elevating temperature from 22 to 50℃increased Cr (VI) reduction with the apparent activation energy (Ea) obtained as 10.6 kJ/mol. Setting a biocathode potential at-300 mV improved the subsequent performance of an MFC for Cr (VI) reduction compared to a control (no set potential). With this set potential, the startup time was reduced to 19 days, the reduction of Cr (VI) was improved to 19.7 mg/(L-d), and the maximum power density was increased to 6.4W/m3 compared to the control (26 days,14.0 mg/(L·d) and 4.1 W/m3). Set potentials of-150 mV and -300 mV also improved system performance and led to similarly higher utilization of metabolic energy gained (PMEG) than set potentials of +200 mV and-450 mV. We observed putative pili at -150 and -300 mV potentials, and aggregated precipitates on bacterial surfaces in both poised and nonpoised controls. These tests show that there are optimal potentials that can be set for developing a Cr (VI) biocathode.This biocathode tubular MFCs equipped with graphite felt electrode successfully achieved PCP degradation with simulatanous power generation. At an initial PCP concentration of 10 mg/L, a PCP reduction rate of 0.11 mg/(L·h) (2.34 mg/(g·h)) with a power production of 0.91 W/m3 were obtained with the achievement of an open potential of 0.23 V.