BES-based biosensors for methane emissions assessment in freshwater ecosystems

Climate change is one of the most important and probable aspects influencing the stability of human societies. Anaerobic carbon oxidation by methane producing bacteria (MPB) in natural and human-made freshwater ecosystems influence the global greenhouse gas (GHG) emissions and its dynamics.  Moreover, these ecosystems are highly sensitive to climate change. However, GHG emissions assessment methodologies are complex and cannot be applied continuously. Thus, better tools to characterize methane emissions and its dynamics in these ecosystems are of capital importance to deal with climate change. Bioelectrochemical systems (BES) are devices that transform the chemical energy of organic and inorganic substrates into electric current thanks to the metabolic activity of the electroactive bacteria (EAB’s). EAB and MPB oxidate the same carbon source (acetate) and, therefore, current produced by EAB can be used as a proxy for methane formation. BES-based biosensors are an interesting type of biosensors since they do not need a transducer, can be manufactured using cost-effective materials and can be applied for real-time and remote location monitoring. The work presented aim to assess the potential use of the electric signal produced by a low-cost, membrane-less BES-based biosensor as an indicator of methane emissions. To this purpose, 3.8L PVC vessels representing a core of a shallow flooded ecosystem were constructed and a BES cell was placed in the centre for the biosensing assessment. Methane emissions were assessed through the close chamber method and analysed by gas chromatography coupled to a flame ionisation detector while the bio-electric signal was continuously recorded. Results show that the methane and the electric production follow a similar pattern, but are displaced in time, being the electric production faster than the methane one. Results indicate that the electric current of a BES-based biosensor has the potential to be used as an indirect measure of methane emissions.