Coupling a photosynthetic microbial fuel cell (PMFC) with photobioreactors (PBRs) for pollutant removal and bioenergy recovery from anaerobically digested effluent

Abstract

Anaerobically digested effluent from food waste (ADE-FW) needs purification treatment due to its high content of ammonium and organic matter. Here, a system that couples a photosynthetic microbial fuel cell (PMFC) with photobioreactors (PBRs) was developed to recover energy from the ADE-FW. First, the ADE-FW was treated in the PMFC for pollutant removal and power generation. The highest power density obtained from the PMFC was about 3.5 W/m3. Power generation was primarily affected by DO and substrate concentrations, which respectively determined the cathode and anode potentials. About 93% of the ammonium in the anolyte was removed in the continuous mode, owing to the ammonium migration effect. Algal biomass in the PMFC increased from 0.1 mg/L to 0.7 mg/L in the continuous mode, which was 27% higher than that in the batch operating mode (0.55 mg/L). Then the effluents from the cathodic chamber were polished in the PBRs. The nitrogen removal rates in the PBRs under continuous and batch operation were 3.0 mg/(L·d) and 1.8 mg/(L·d), respectively. In terms of energy production, more algal lipid energy was obtained in the continuous mode, but less electricity was obtained in this mode. Consequently, the total energy produced in the coupled systems in the continuous and batch modes were consistently about 1.8 kWh/m3. The high pollutant removal rate and energy recovery efficiency of the coupled system indicated that it would be a practical technology for the industrial-scale applications.