Mitigating <scp>VFA</scp> accumulation in hydrogen‐assisted anaerobic digestion through <scp>MEC</scp> integration

Abstract BACKGROUND Biological hydrogenotrophic methanization is a promising method to improve biogas quality in anaerobic digestion systems. However, hydrogen‐assisted anaerobic digesters (AD‐H 2 ) are prone to volatile fatty acid (VFA) accumulation and process instability. There is a need for solutions to mitigate the risks associated with hydrogen addition in anaerobic digestion while harnessing its benefits. This study aimed to investigate whether microbial electrolysis cell (MEC) integration can mitigate VFA accumulation caused by hydrogen addition in AD systems. RESULTS Results revealed that the integration of the MEC increased methane yield in a hydrogen‐assisted anaerobic digester (i.e. a MEC‐H 2 system), achieving 391.80 mL CH 4 per g of COD removed (COD r ). In comparison, the AD‐H 2 reactor produced 334.42 mL CH 4 /g COD r . Additionally, about 45.04% less acetate was observed in the MEC‐H 2 compared to the AD‐H 2 system, while concurrently, residual COD was lower in the MEC‐H 2 system by 39.10% and 27.40% compared to the AD‐H 2 and conventional AD reactors, respectively. CONCLUSION The integration of MEC with the AD‐H 2 promoted the enrichment of acetoclastic methanogens (Methanotrix genus) on the cathode surface, which supports the view that the enhanced methane production in MEC systems is due to the effective degradation of VFAs via direct electron transfer. Integrating an MEC with a hydrogen‐assisted anaerobic digestion system can provide more stable reactor performance and higher bioenergy production. © 2026 The Author(s). Journal of Chemical Technology and Biotechnology published by John Wiley &amp; Sons Ltd on behalf of Society of Chemical Industry (SCI).