Long-term performance of pilot-scale tubular plant-microbial fuel cells in a brownfield-constructed wetland

The plant-microbial fuel cell (P-MFC) is a suitable stand-alone power source for low-power (mW) electronics. P-MFCs have been studied extensively under laboratory conditions. Some studies investigated P-MFCs under field conditions, usually on a small scale or for a short time. The objective of this research was to identify the performance of the tubular P-MFC over a period of years during the establishment of a constructed wetland from a brownfield that was fed with water from a ditch. The performance of tubular P-MFCs with seven different commercially available electrode materials, different depth below the surface, tube length, as well as tube diameter, was investigated by measuring voltages and temperature, as well as by performing polarization measurements. With a maximum of 13–18 mW/m2 projected plant surface, or 1.1 mW for a 1m tube, the tubular P-MFC is expected to be a suitable power source for remote sensing equipment. The performance of the tubular P-MFC is correlated to temperature and decreases significantly at temperatures below 6 °C. Longer tubular P-MFCs produce more power, but less power per meter, where the optimum tube length seems to be around one to 2 m. Longer tubes experience higher losses due to material resistance. The tubular P-MFC design is not so sensitive to different electrode material choices, and smaller P-MFCs seem to perform relatively well. To utilize P-MFC power for sensor applications, an appropriate harvester should be designed that is able to find the maximum power point of the P-MFC while harvesting and has sufficient buffer capacity in case of temperature and seasonal variations.