Influence of electrode spacing and fed-batch operation on the maximum performance trend of a soil microbial fuel cell

The effect of electrode spacing on a soil microbial fuel cell (MFC) performance under fed-batch treatment with synthetic urine medium (SUM) was investigated at 2, 5, and 8 cm electrode spacing. The electrodes consisted of stainless-steel mesh with coarse layers of carbon-black. The MFCs were fed with SUM when the natural substrate of the medium was exhausted. Initial feeding resulted in 79.6, 108.7, and 103.1% increase in OCV with a proportional percentage increase in power at 2, 5, and 8 cm electrode spacing. Six days after the first feeding, the power was 189.9, 150.7, and 108. 5 mW/m 2 in ascending order of electrode spacing. With more extended treatment, the overall maximum power was obtained at 8 cm spacing. In ascending order of electrode spacing, the highest power (207.92, 263.38, and 271.1 mW/m 2 ) was obtained on days 39, 42, and 93, respectively. The study shows that a larger anode-to-cathode distance requires a longer time for the soil MFC to achieve stable and maximum performance in fed-batch operation. • Soil MFC is optimized for efficient substrate utilization and long-term sustainable power generation. • The effect of long-term fed-batch operation on the MFC performance with varying electrode spacing is investigated. • Soil MFC performance stability is time dependent on electrode spacing under fed-batch operation. • Smaller electrode spacing results in initially better performance due to lower internal resistance. • Larger electrode spacing takes a longer time for the MFC to reach stable and maximum performance.