Electricity generation from fermented primary sludge using single-chamber air-cathode microbial fuel cells

Single-chamber air-cathode microbial fuel cells (MFCs) were used to generate electricity from fermented primary sludge. Fermentation (30 °C, 9 days) decreased total suspended solids (26.1–16.5 g/L), volatile suspended solids (24.1–15.3 g/L) and pH (5.7–4.5), and increased conductivity (2.4–4.7 mS/cm), soluble COD (2.66–15.5 g/L), and volatile fatty acids (1.9–10.1 g/L). To lower the COD and increase pH, fermentation supernatant was diluted with primary effluent before being used in the MFCs. The maximum power density was 0.32 ± 0.01 W/m2, compared to 0.24 ± 0.03 W/m2 with only primary effluent. Power densities were higher with phosphate buffer added to the supernatant (1.03 ± 0.06 W/m2) or the solution (0.87 ± 0.05 W/m2). Coulombic efficiencies ranged from 18% to 57%, and sCOD removals from 84% to 94%. These results demonstrated that sludge can effectively be used for power generation when fermented and then diluted with only primary effluent.