Micro–Nano Magnetite-Loaded Biochar Enhances Interspecies Electron Transfer and Viability of Functional Microorganisms in Anaerobic Digestion

Magnetite-loaded biochar generated by gasification serves as a potential additive to facilitate electron transfer and boost methane production. In this study, the focus was placed on the mechanism of magnetite-loaded biochar-enhanced methanogens with live bacteria in real habitats, and the connection between live microorganisms and the methanogenic pathway was revealed. Magnetite-loaded biochar produced at a FeCl3-to-woodchip ratio (w/w) of 15/100 presented maximal methane production, where the daily methane yield was improved by 157% compared with the control. Magnetite accelerated the consumption of short-chain fatty acids through dissimilatory iron reduction, and it was converted into siderite and goethite after anaerobic digestion. The iron cycle coupling with the organic removal enhanced electron transfer efficiency and further transmitted electrons to promote methanogenesis. As indicated from the results, live high DNA (Atelge, M. R.; Atabani, A. E.; Banu, J. R.; Krisa, D.; Kaya, M.; Eskicioglu, C.; Kumar, G.; Lee, C.; Yildiz, Y. Ş.; Unalan, S.; et al. Fuel 2020, 270, 117494.) cells with high viability increased from 21 to 44%, which probably facilitated the electron transfer and direct interspecies electron transfer via membrane proteins. Moreover, the activities of the functional enzyme participating in the acetoclastic and hydrogenotrophic methanogenic pathways were enhanced. As revealed from the gene abundance from live microorganisms of the acetoclastic/hydrogenotrophic methanogenic pathway, the magnetite-loaded biochar facilitated the methanogenesis process, probably due to the DIET formed between the iron reduction bacteria Ruminococcaceae and methanogenesis Methanothrix and Methanosarcina by the magnetite-loaded biochar.