Impacts of intermittent electrical stimulation on continuous electro-anaerobic digestion from wastewater: performance...

The recently reported electro-anaerobic digestion with intermittent electrical stimulation (IEAD) offers new opportunities for renewable energy storage. However, the mechanistic insights and resilience of long-term continuous and stable IEAD are still yet to be better understood. This study lasted up to 155 days of continuous operation of IEAD in up-flow anaerobic sludge blanket bioreactors to evaluate the long-term effects of different intermittent power periods on IEAD performance. The optimal electrical stimulation period was obtained for 12 h:12 h intermittence, resulting in a 15.9 % improvement of the specific methane yield while achieving an organic removal efficiency higher than 98 %. Intermittent electrical stimulation favored biofilm growth, electroactive substance secretion, and enhanced electrochemical activity and cellular repair. Genomic analysis demonstrated that IEAD microbial community was dominated by Methanothrix, whereas continuous energization promoted Methanobacteriaceae enrichment. Proteomic analysis suggested that intermittent power supply preserved functional proteins and upregulated dominant enzymes such as acetyl-CoA carboxylase biotin carboxyl carrier protein and enoyl-CoA hydratase, while conferring flexible carbon source allocation and electron transfer capacity to the suspension zone. Life cycle assessment results showed that the IEAD system could achieve an energy conversion rate of 20.6 and low carbon emissions of 7.3 g CO_2-eq/MJ.