Potential of direct interspecies electron transfer in synergetic enhancement of methanogenesis and sulfate removal in an up-flow anaerobic sludge blanket reactor with magnetite

Anaerobic digestion (AD) has been widely applied in the treatment of industrial wastewater containing oxidized sulfur compounds. However, the production of hydrogen sulfide usually limits the syntrophic metabolism proceeded by interspecies hydrogen transfer (IHT), due to its corrosive and toxic properties. The current study was in an attempt to establish direct interspecies electron transfer (DIET) to resist the toxic inhibition from hydrogen sulfide and keep syntrophic metabolism stable. The results showed that, in the presence of magnetite, the methane production was improved about 3-10 folds at each ratio of COD/SO42, while the enhancement of methanogenesis had almost no negative effect on sulfate reduction. With magnetite, the sludge conductance increased about 3 folds, but the concentration of c-type cytochromes decreased, suggesting that the potential DIET via both electrically conductive pili and outer surface c-type cytochromes was established. Microbial community revealed that, Veillonella species, the Fe(III)-reducing genus capable of reducing sulfate to hydrogen sulfide, were specially enriched with magnetite. Together with the relatively higher abundance of Methanothrix and Methanosarcina species, the novel DIET between Fe(III)/sulfate-reducing genus and methanogens was inferred to be responsible for the synergetic enhancement of methanogenesis and sulfate removal. (C) 2019 Elsevier B.V. All rights reserved.