Abstract
Microbial fuel cells (MFCs) are an evolving technology built around the idea of treating waste water while simultaneously generating a sustained power output. A large focus has been placed on known electrogens such as Shewanella oneidensis and Geobacter sulfurreducens, while very little is understood about how species interact together in a microbial community. While inoculating MFCs with naturally occurring communities is one method of studying fuel cells, this work took a different approach and attempted to build a synthetic community based upon a naturally occurring community. This will be important in the future of MFCs since being able to tailor a community to the influent feed will theoretically allow a more efficient use of the substrates and a higher level of treatment to be achieved. The synthetic community was made up of 5 different species, modelled on a naturally occurring microbial community. This was carried out through a number of single species, dual-species and 5-species MFC experiments. This will allow the electrogenic ability and the community’s ability to treat wastewater to be compared between single species and communities. The single-species MFCs demonstrated the electrogenic potential of three previously unstudied species. It was also observed that the single species MFCs produced higher power than the dual-species and 5-species communities. This contradicts the commonly held view that as biodiversity increases, power output increases. In the dual-community MFCs, a trend emerged where the species which produced the highest power outputs were associated with MFCs containing a fermentative species and an anaerobic respirator, while the lowest powers were observed in dual-cultures made up of two fermentative species. Cyclic voltammetry showed that the studied species did not produce extracellular mediators and the electrogenic activity occurred in the biofilm. It was also shown that as the biodiversity of the community increased, so did the level of chemical oxygen demand (COD) removal, with the 5-species community achieving the highest COD removal of 90% compared to the 70% of the single species. Metabolic experiments were carried out using a Biolog Omnilog on the individual species and 10 dual species combinations to try and understand the different substrates utilised by individual species. This was done by comparing respiration rates and lag times for the individual substrates which are relevant to MFC experiments. It was observed that faster growth rates but longer lag times were generally observed when two species tried to utilise the same substrate, but the results did not correlate with the results generated from the MFC experiments.