Electrifying anaerobic granular sludge for enhanced waste anaerobic digestion and biogas production

Bioelectrochemical anaerobic digestion (BEAD) is an attractive way to enhance biogas production in the anaerobic digestion process. Exploring cost-effective biocatalysts with remarkable catalytic ability is a pivotal issue for the industrial application of BEAD systems. In this study, intact anaerobic granular sludge (AGS) was employed as a biocatalyst in an attempt to achieve high-efficiency CH4 production via interactions between exoelectrogens and methanogens. The biogas production in the BEAD system was optimized by controlling the applied voltage (0, 0.6, 0.8, and 1 V) and acetate load (1000, 5000, and 10000 mg/L). The CH4 production rate increased with applied voltage and acetate loading, while the overall energy efficiency was the highest at an applied voltage of 0.8 V and an acetate load of 5000 mg/L. The BEAD system with AGS as the biocatalyst was also efficient for the degradation of highly concentrated organic waste, with an average methane production rate of 86.23 ± 7.12 L/m2/d and CH4 content as high as 88.87%. Microbial communities including organic-degrading bacteria and exoelectrogens (e.g., Syntrophomonas, Geobacter) and hydrogenotrophic methanogenic archaea (r.g., Methanobacterium) were enriched at the anode and the cathode, respectively. The AGS-based BEAD system represents a promising industrial application in biogas production.