Intermittent electrostimulation-modified direct interspecies electron transfer for enhanced methanogenesis in anaerobic digestion of sulfate-rich wastewater

Abstract

Methane recovery and organics removal in sulfate (SO42−)-rich wastewater anaerobic digestion are hindered by electron competition between methanogenesis and sulfidogenesis. Here, intermittently electrostimulated bioelectrodes were developed to facilitate direct interspecies electron transfer (DIET)-driven syntrophic methanogenesis, increasing substrate competition among methanogenic archaea (MA). By optimising the electrochemical environment, MA was able to employ electron transfer more efficiently than sulfate-reducing bacteria (SRB), resulting in significant methane accumulation (58.1 ± 1.0 mL-CH4/m3reactor) and COD removal (90.5 ± 0.5 %) at lower COD/SO42− ratio. Intermittent electrostimulation improved the metabolic pathway for electroactive bacteria to utilize acetate and direct electrons to electrotrophic MA, decreasing SRB abundance and affecting the sulfate reduction pathway. Intermittently electrostimulated biofilms significantly increased gene levels of key enzymes in electron transport for cytochrome and e-pili biosynthesis, crucial for DIET, demonstrating enhanced DIET-driven syntrophic methanogenesis. This study provides a strategic approach to optimize methanogenesis in sulfate-rich wastewater anaerobic digestion.