Influence of ionic conductivity in bioelectricity production from saline domestic sewage sludge in microbial fuel cells

•Seawater based domestic wastewater sewage sludge (SWS) was used as a MFC substrate.•EC of the SWS can be adjusted using freshwater based domestic sewage sludge (FWS).•Mixed sludge yielded a peak power density of 41Wm−3 and CE of 28.6%.•EC of ∼12mScm−1 and the lower internal resistance enhanced the power density. This study aimed at manipulating ionic conductivity (EC) to harvest the maximum electrical energy from seawater-based domestic wastewater sewage sludge (SWS), unique to only a few cities, through microbial fuel cell (MFC). SWS has never been investigated as a MFC substrate before, and thus the influence of high in-situ EC on the energy recovery was unknown. In this study, the EC of the SWS was reduced through mixing it with fresh water-based domestic wastewater sewage sludge (FWS) or diluted 50% using deionized water while FWS and SWS were individually served as reference treatments. SWS:FWS mix (1:1) exhibited a maximum Coulombic efficiency of 28.6±0.5% at a COD removal of 59±3% while the peak power density was 20-fold higher than FWS. The improved performance was due to the lower ohmic internal resistance (36.8±4.2Ω) and optimal conductivity (12.8±0.2mScm−1). Therefore, dilution with FWS could enhance energy recovery from SWS.