Selection of waste-derived inocula for CO2 bio-electro-recycling: Integration of microbial electrosynthesis and anaerobic digestion on charcoal functionalized electrodes

Abstract

Microbial electrosynthesis (MES) has been widely used to produce volatile fatty acids (VFAs) from CO₂. In this technology, the applied potential, the source of the inoculum, and the cathode material are key parameters influencing process performance. This study evaluated different waste-derived inocula to identify the most effective one, which was then used as inoculum in MES bioreactors equipped with activated charcoal-functionalized cathodes at different cathodic potentials: −0.8 V and − 1.0 V vs Ag/AgCl to promote acetate production. Physicochemical parameters were continuously monitored and microbial community composition was characterized. MES experiments were conducted in double-chamber bioreactors using 100 % v/v CO₂ feed. The system operating at −1.0 V outperformed the one at −0.8 V MES, converting 60.4 ± 5.1 % of CO₂ into acetic acid, with a daily production rate of 98.6 ± 7.5 mg L⁻¹ d⁻¹. Productivity was used to estimate the CO₂ emission from biogas from Italian anaerobic digestion plants that can be avoided by converting this CO₂ into acetate.