Cascading Integration of Electrofermentation and Photosynthesis—Low-Carbon Biorefinery in Closed Loop Approach

Abstract

Single-chambered electrofermentation (EF) bioreactors are operated using spent wash to evaluate the effect of applied voltage (EF/AV; −0.6 V) against closed-circuit (EF/CC; 100 Ω) and control (EF/C; no voltage/resistance) operations using deoiled microalgae biomass-derived biochar electrodes (anode) on increasing acidogenesis rate/efficiency. Higher total volatile fatty acids (VFA) production (mg L−1) is observed in EF/AV (2866), depicting 31% and 57% increments than EF/CC (1984) and EF/C (1224), respectively. The VFA profiles (C2–C4) in EF/AV are higher with acetic/butyric/propionic acids (1922/704/240 mg L−1) and biogas co-generation [H2 (22%) and CH4 (3%)] than EF/CC and EF/C. The applied voltage (EF/AV) helps in electron flux regulation for increasing substrates conversion and VFA generation. Residual VFA-rich effluents from EF process is utilized as substrate to mixotrophic microalgae cultivation (nutrient- and stress-phase) that resulted in biomass production with simultaneous wastewater treatment. EF/AV depicts higher biomass growth (0.72 g L−1; 4th day) and substrate removal (63%) than other operations. Integrations of electrofermentation with photosynthetic processes operated with the residual resources in effluents towards product valorization and wastewater polishing, accounts for low-carbon economy.