How biofilms can produce current
EABs may have applications in biosensors and microbial fuel cells. They are essentially a film of microorganisms able to supply electrons for electricity, but the exact mechanism of this electron transfer process remains poorly understood. The EU-funded project 'Electroactive biofilms for microbial fuel cells and biosensors' (EA-BIOFILMS) was set up to enhance knowledge in this area so that reliable EAB-based technologies can be developed. Researchers studied model metal-reducing microorganisms such as Shewanella sp. and Geobacter sp. Both of these have structures in their outer membranes that allow for direct electron transfer between itself and an electrode. The project also advanced the first spectroelectrochemical method for the in vivo characterisation of EABs, which researchers successfully applied to the Geobacter biofilms. The method allows for rapid and informative studies, with minimal pre-treatment or destruction of the biofilm. For Shewanella, researchers discovered that electrons are indirectly transferred in young biofilms (this produces more current), but that the process becomes mostly direct as the biofilm ages. In general, electron transfer is also very rapid in thin biofilms. The knowledge gained during this project will aid the industrial scale-up of EAB-based devices as researchers now better understand how to optimise biofilm efficiency. It will also inform the design of fuel cells for the recovery of energy from wastewater, as well as biosensors for monitoring drainage water.
