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 (C ₂ –C ₄ ) in EF/AV are higher with acetic/butyric/propionic acids (1922/704/240 mg L ⁻¹ ) and biogas co‐generation [H ₂ (22%) and CH ₄ (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 ; 4 ^th 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.