Novel pyrrhotite and alum sludge as substrates in a two-tiered constructed wetland-microbial fuel cell

Abstract

Integrated constructed wetland-microbial fuel cells (CW-MFCs) use exoelectrogenic bacteria to transform the energy inherently existed in wastewater into bioelectricity and simultaneously remove the contaminants in wastewater. They have the potential to provide a solution for both water and energy challenges. In this study, a novel two-tiered CW-MFC system consisted of a dewatered Al-DWTR-based up-flow CW-MFC (Top CW-MFC) and a pyrrhotite-based downflow CW-MFC (Bottom CW-MFC) was constructed. The two-tiered CW-MFC system was operated under different COD concentrations, HRTs and operation modes over a 477-day trial. The treated effluent had an overall average COD concentration of 69.05 mg/L. High power density of the top CW-MFC of 741.36 mW/m3 (A1-C) and 339.56 mW/m3 (A2-C) at HRT of 2.49 d (Phase 7) with continuous flow and 1162.63 mW/m3 (A1-C) and 352.34 mW/m3 (A2-C) with tidal flow (Phase 10), respectively, was achieved. Co-occurrence of Feammox and iron sulphide-based denitrification were found in bottom CW-MFC, leading to the enhanced nitrogen removal in the system. The genera of SRB (Desulfosporosinus, Desulfobulbus, Desulfobacca, Desulfovibrio and members of Desulfobacteraceae), exoelectrogenic bacteria enriched in the system resulted in a low release of sulfate, and effective pollutant removal and bioelectricity production. The findings highlight the novel two-tiered CW-MFC system for efficient wastewater treatment and high performance of energy extraction, supporting a clean environment.