Optimization Of Microbial Fuel Cell Separator, Air-cathode And Configuration

Microbial fuel cells (MFCs) are devices which can generate electricity frombiomass using electrochemically active bacteria, and have drawn increasing attention asa promising technology for wastewater treatment and energy recovery. Air-cathode,single-chamber MFCs have the great potential for practical applications due to the factthat they directly use oxygen in air as electron acceptor producing water, and noaeration or chemical regeneration is needed. The main challenges for practicalapplication of MFCs are to increase the power and the recovery of electronsfrom the substrate (coulombic efficiency, CE), and reduce the cost of thematerials. In this dissertation, separator characteristics were systematicallyexamined, and air-cathode structure and MFC reactor configuration wereoptimized, in order to enhance the power production and CE.Separator properties affecting MFC performances were identified, including protontransfer, oxygen transfer and ohmic resistance. Various separator materials, includingglass fiber, nylon, J-Cloth, anion exchange membrane (AEM) and cation exchangemembrane (CEM), were systematically examined and compared. Glass fiber showeda high proton transfer coefficient, a low oxygen transfer coefficient, and a low ohmicresistance, and it is non-biodegradable. Using glass fiber as separator in air-cathodeMFCs shortened start-up time, enhanced the anode performance, reduced cathodebiofouling, and increased power generation and CE.Effect of the separator pore size on the maximum power densities produced usingnylon as separators was further investigated. Nylon separators led to an increase inpower density with pore sizes increasing from0.2to160μm, while the CE wasinversely correlated to the power density. It was found that AEM and CEMdeformed in air-cathode MFCs resulting in poor power generation. To correctthis, stainless steel mesh was used to press the membrane flat against thecathode. Power densities of MFCs were significantly enhanced, and AEMworked better than CEM.Air-cathode structure was optimized in glass fiber separator coupled MFCs. Basedon polytetrafluoroethylene (PTFE) as materials for wet-proofing and diffusion layers, it was shown that the cathode performance with different percentages of carbon clothwet-proofing and numbers of diffusion layers was directly related to conditions thatincreased oxygen transfer. For new air-cathode design in MFCs constructed withseparators, the cathode should have the minimum number of diffusion layers thatprevent water leakage and maximize oxygen transfer to the cathode. New air-cathodeswere developed based on fluorinated ethylene propylene (FEP) for carbon clothwet-proofing and diffusion layers, which showed a better performance than PTFE basedair-cathode.Glass fiber separator and air-cathode were integrated here to create a double-sidesMFC architecture. Electrode space was significantly reduced and thus the internalresistances of MFC decreased, resulting in that the MFC steadily generated an enhancedpower density with a high CE of91%. This MFC configuration is useful for scaling upair-cathode MFC system design.