A critical review of microbial electrolysis cells coupled with anaerobic digester for enhanced biomethane recovery from high-strength feedstocks

Anaerobic digestion (AD) is considered as a traditional method for biomethane recovery from high-strength waste and wastewater. The limitations of conventional anaerobic digestion processes include sluggish kinetics, process instability, and low methane yield. Recently, microbial electrolysis cell (MEC) has been demonstrated as a promising approach for enhancing biomethane recovery from various organic feedstocks. In recent years, a variety of hybrid anaerobic bioreactors coupling MEC and AD were employed to improve biomethane recovery and anaerobic treatability of various high-strength feedstocks. The MEC-AD integrated systems also exhibited better process stability than traditional anaerobic digesters by alleviating the accumulation of short-chain volatile fatty acids at higher organic loading rates, as well as mitigating the inhibitory effects of various toxic and refractory compounds. Firstly, this article provides a comprehensive performance review of the MEC-AD systems treating various high-strength (>8 g COD/L) substrates. Secondly, the implications of process parameters, energy efficiencies, and microbial community characteristics are discussed. Finally, valuable operational insights and future research needs are highlighted.