In search for appropriate processes to enhance the efficiency of municipal sewage plants, microbial fuel cells (MFC) have moved into research focus. Due to the MFC characteristic, which is able to treat wastewater while generating power simultaneously, it is also a promising approach to change the energy balance of sewage plants – switching from the biggest municipal energy consumer to an energy producer.

Owing to the small power density of MFCs in comparison to chemical fuel cells, large active surface areas and therefore low-cost cell constructions, electrodes and catalysts are necessary.

Challenges in MFC upscaling have been overcome and a functional and less price intensive cell design for integration in existing aeration tanks of municipal wastewater treatment plants has been developed (figure left). The new cell design integrates a double-sided graphite/polymer composite anode between two cathodes, to enlarge the surface area. It allows online half-cell potential measurement and biofilm flushing by nitrogen (figure right), among other options. High performance catalytic active cathodes are used, which are produced in-house by a semi-automatic production line.

A fuel cell stack of up to fifty MFCs, each with an active area of 6000 square centimeters respectively, has successfully started operation with real municipal wastewater at the wastewater treatment plant in Goslar, Germany.

In addition to the technical cell design, the wastewater parameters strongly affect the electrochemical performance of microbial fuel cells. Therefore the influences of process parameters (temperature, pH, O₂, TOC etc.) were measured to determine optimized operating points when fed by real wastewater.

Additionally cathodic catalysts influence the MFC performance considerably, so the electrode-performance of the scaled up microbial fuel cells were investigated by half-cell measurements.