In a renewable energy system, renewable electricity that is produced is excess needs to be stored not to get lost. Besides, carbon-neutral fuels need to be produced, to become independent of biomass and to avoid a further increase of CO2-levels in the atmosphere.
In this thesis, a methane-producing Bioelectrochemical System (BES) was studied: a technology in which microorganisms grow on an electrode and catalyse the conversion of CO2 and renewable electricity into renewable methane. The technology could be operated long-term (188 days) at a methane production rate of 6 L/m3 reactor per day and energy efficiency of 3.1% (at -0.55 V vs. NHE). Most energy was lost at the electrode. At the conditions studied, methane was mainly produced indirectly using hydrogen as electron donor. Bacteria likely produced the hydrogen. We show that BESs can also be used to produce medium chain fatty acids from acetate, using electricity as electron donor.