Rapid Biocathode Start-Up with Mixed Methanogenic–Electroactive Inocula for Enhanced Bioelectrochemical Performance

This study explores the use of a pre-acclimated Geobacter-enriched inoculum as a novel strategy to accelerate the start-up of biocathodes. Unlike conventional inoculation with broad-spectrum communities, the proposed inoculum combines a long-term electroactive consortium, previously adapted to anaerobic bioelectrochemical conditions, with digestate produced under controlled laboratory conditions. This prior acclimation ensures the presence of Geobacter strains already conditioned to electrode-associated growth, promoting rapid colonization and early electrochemical activity. Experiments were conducted in a dual-chamber electrochemical cell equipped with a three-electrode setup polarized at −1 V vs. Ag/AgCl. The enriched biocathode reached current densities exceeding 1.4 A/m2 within 24 h, whereas the control exhibited significantly lower, less stable, and inconsistent performance. Unlike previously reported approaches based on broad-spectrum co-inoculation, this work presents a tailor-made inoculum in which the electroactive community is not only dominated by Geobacter, but also selectively preconditioned under functional bioelectrochemical conditions. This prior adaptation is a key differentiator that markedly enhances start-up efficiency. The results demonstrate that strategic enrichment with pre-acclimated Geobacter significantly accelerates start-up and improves electrochemical performance, offering a promising pathway toward more efficient and scalable bioelectrochemical systems for wastewater treatment and renewable energy generation.