AbstractMicrobial fuel cell (MFC) systems capable of both treating wastewaters and recovering energy have the potential for successful scale-up as a low carbon technology. These systems utilize microorganisms residing in biofilms as biocatalytic agents in the conversion of reduced substrates to electrical energy. As such, it is important to understand how MFC anodic biofilms develop over time and also how environmental parameters such as substrate type, temperature, carbon support material, anode architecture and optimized applied potentials also affect electrogenic performance.
The type of substrate was found to have a large impact on the acclimation and performance of electrogenic biofilms. Acetate produced the highest power density of 7.2 W m 3 and butyrate the lowest at 0.29 W m"3, but it was also found that biofilm acclimation to these different trophic conditions also determined the MFC response to different substrate types i.e. both acetate and butyrate substrates produced power densities of 1.07 and 1.0 W m"3 respectively in a sucrose enriched reactor.
The use of MFCs for wastewater treatment in temperate regions requires the development of reactor systems that are robust to seasonal fluctuations and are energy efficient. As such, system performance was examined at three different operating temperatures (10°C, 20°C and 35°C). At each temperature a maximum steady-state voltage of 0.49 V ± 0.02V was achieved after an operational period of 47 weeks, with the time to reach steady-state voltage being dependent on acclimation temperature. The highest COD removal rates of 2.98g COD L^d * were produced in the 35°C reactor but coulombic efficiencies (CE) were found to be significantly higher at pyschrophilic temperatures. Acclimation at different operating temperatures was found to a have a significant effect on the dynamic selection of psychrophilic, psychrotolerant and mesophilic anode respiring bacteria (ARB) and also influence the development of biofilm biomass, methanogenesis and electrogenic activity. Although start-up times were inversely influenced by temperature the amount of biomass accumulation increased with higher operational temperatures and this had a direct impact on biocatalytic performance.
The three dimensional structure and porosity of different carbon anode materials affected anodic performance by determining the levels of surface area available for biofilm growth and the capacity for mass transfer to occur. Novel helical electrode configurations were used to look at the effect of altering turbulent flows to increase mass transfer rates and carbon surface areas available for electrogenic growth. The spiral with the highest amount of carbon veil and the smallest gap produced the highest power production of 11.63 W m"3 .
Comparative studies of a logic controlled and un-controlled external load impedance showed that control affected the biocatalyst development and hence MFC performance. The controlled MFC better optimized the electrogenic anodic biofilm for power production, indicating that improved power and substrate conversion can be achieved by ensuring sustainable current demand, applied microbial selection pressures and near-optimal impedance for power transference.
|Date of Award
|Jung Rae Kim (Supervisor), Giuliano Premier (Supervisor), Alan Guwy (Supervisor) & Richard Dinsdale (Supervisor)
- Microbial fuel cells
- Microbial biotechnology
- Biomass energy
- Renewable energy sources