Enhancing biomethane production and pyrene biodegradation by addition of bio-nano FeS or magnetic carbon during sludge anaerobic digestion

Pyrene exerts toxic effects on methanogens during anaerobic digestion of sludge, thus affecting the efficiency of sludge treatment. This study evaluated the facilitated direct interspecific electron transfer (DIET) between bacteria and methanogens when bio-nano FeS or magnetic carbon is added into anaerobic reactors. Results showed that adding 200 mg/L bio-nano FeS or magnetic carbon clearly reduced the accumulation of short-chain fatty acids and avoided acidification during 25 days of anaerobic digestion. The methane productions were 98.38 L/kg total solid (TS) and 73.69 L/kg TS in the bio-nano FeS and magnetic carbon systems, respectively, which accelerated methane production by 58.1% and 33.4%, respectively, compared with the control system (40.26 L/kg TS). The pyrene removal rates reached 77.5% and 72.1% in the bio-nano FeS and magnetic carbon systems, whereas it was only 40.8% in the control system. Analysis of microbial community structure revealed that methanogens (e.g. Methanosarcina and Methanosaeta) and extracellular electron-transfer bacteria (e.g. Pseudomonas, Cloastridia, and Synergistetes) were enriched in the reactors added with bio-nano FeS or magnetic carbon. This result indicates that the addition of bio-nano FeS or magnetic carbon may promote the activity and growth of microorganisms to improve the efficiency of methane production and pyrene degradation by enhancing DIET.