Establishment of an Electroactive Microorganism Community in Anaerobic Digestion with Photosynthetic Bacteria Agents for Promoting Methane Production

Efficient electron transfer among anaerobes is critical to maintaining the high performance of anaerobic digestion. In this study, photosynthetic bacteria (PSB), as exoelectrogenic bacteria, were added to a light anaerobic digester to establish the electroactive microorganism community for the improvement of methane production during anaerobic digestion. Results showed that the daily methane production increased by 37% and the chemical oxygen demand (COD) removal efficiency increased from 70% to over 90%, accompanied by the increase of F420, ATP, and NADH/NAD+ of the sludge. The electrochemical activity of the anaerobic sludge such as capacitance and conductance increased by 28 and 16%, respectively, and the extracellular electron transfer capacity of the sludge nearly doubled. In addition, the PSB agents promoted the secretion of conductive proteins and EPS, such as the OmcS copy number increasing more than 100 times, which provided a bridge for electron transfer between other microorganisms in the sludge. Correspondingly, PSB promoted the enrichment of electrotrophic methanogens, Methanosarcina, whose abundance increased from 0.76 to 34.7%. Also, it increased the proliferation of other exoelectrogenic bacteria such as Syntrophomonas. In brief, a mutually beneficial electroactive community was established by the addition of PSB agents to facilitate electron transfer for methane production during anaerobic digestion.