Bioelectrochemical stimulation enhances methane production and microbial stability in anaerobic digestion

Bioelectrochemically improved anaerobic digestion (AD-BES) is a promising strategy to intensify biogas production and enhance process stability, yet validation on real feedstocks at relevant scale remains limited. This study compares a continuously fed AD-BES treating liquid agricultural digestate with a conventional AD reactor. Both reactors were operated under progressively reduced hydraulic retention times (HRTs) of 40, 30 and 20 days to assess their performance under intensified conditions. Electrochemical monitoring confirmed biofilm establishment on both electrodes. While methane production in control AD decreased at lower HRTs, AD-BES improved its performance, showing a 25% higher methane production at HRT 30 and a 22% higher one at HRT 20. The specific methane yield reached 46 L-CH₄·kg-COD_added^-1. Anodic Coulombic efficiency ranged from 7 to 16%, while 8-12% of the methane was produced bioelectrochemically. Microbial analysis revealed that both electrodes hosted similar biofilms enriched in fermentative Firmicutes, including Gallicola and W5053, taxa associated with electroactive niches. The AD-BES digestate maintained a stable microbial structure across the different HRT reductions, while the control AD exhibited pronounced shifts (e.g., Fastidiosipila). qPCR confirmed strong enrichment of methanogenic markers on both the electrodes. Overall, AD-BES maintained methane productivity at reduced HRT, showing higher methane production than traditional AD.