Loading rate and external resistance control the electricity generation of microbial fuel cells with different three-dimensional anodes

The electricity generation, electrochemical and microbial characteristics of five microbial fuel cells (MFCs) with different three-dimensional electrodes (graphite and carbon felt, 2 mm and 5 mm graphite granules and graphite wool) was examined in relation to the applied loading rate and the external resistance. The graphite felt electrode yielded the highest maximum power output amounting up to 386 W m−3 total anode compartment (TAC). However, based on the continuous current generation, limited differences between the materials were registered. Doubling the loading rate to 3.3 g COD L−1 TAC d−1 resulted only in an increased current generation when the external resistance was low (10.5–25 Ω) or during polarization. Conversely, lowering the external resistance resulted in a steady increase of both the kinetic capacities of the biocatalyst and the continuous current generation from 77 (50 Ω) up to 253 (10.5 Ω) A m−3 TAC. Operating a MFC at an external resistance close to its internal resistance, allows to increase the current generation from enhanced loading rates while maximizing the power generation.