Influence of ferric oxides with varying crystallinity on the enrichment of halophilic exoelectrogens: An application for power generation in microbial fuel cells

Abstract

Pre-enriching electroactive microbes (EAM) capable of respiration using solid terminal electron acceptors (TEA) is a prospective strategy that promotes faster start-up of bioanodes in microbial fuel cells (MFC) for energy-efficient treatment of saline wastewater. Previous studies demonstrated a reduction in the start-up times of bioanodes with ferric oxides as TEA, though the enriched EAM generated a wide range of current densities as opposed to those using graphene oxide (GO) as TEA. Additionally, the influence of ferric oxides with varying crystallinity on the anode-respiring activity of halophilic EAM is understudied. This study elaborates a systematic investigation into the influence of inoculum sources, different crystallinity of ferric oxides and their redox potentials on the selective enrichment of GO-respiring EAM for developing bioanodes with high current-generating capacity at shorter start-up times. A holistic assessment of the bioanodes, including analysis of their electrochemical performance and generated power densities, revealed that enrichment of GO-respiring EAM with amorphous ferrihydrite as TEA fostered the growth of high-performing biofilms at shorter start-up times (48–72 h) compared to crystalline goethite used as TEA (∼96 h). These biofilms produced power densities ranging from 142 ± 10 mW/m2 to 276 ± 76 mW/m2 with corresponding Coulombic efficiencies of 16 ± 6 % to 30 ± 6 %. Finally, the implications of promising halophilic EAM consortia were explored for saline MFC as a prospective energy-neutral wastewater treatment technology.