Ferroferric oxide triggered possible direct interspecies electron transfer between Syntrophomonas and Methanosaeta to enhance waste activated sludge anaerobic digestion

Abstract

ZVI was reported to enrich H₂-utilizing methanogens that enhanced interspecies H₂ transfer, while Fe(III) oxide served as a conductive material to promote direct interspecies electron transfer (DIET). However, the interaction of these two modes in anaerobic digestion has not been clarified yet. In this study, when adding Fe₃O₄ and ZVI simultaneously into an anaerobic digester, the abundance of hydrogenotrophic methanogens decreased drastically compared to ZVI-added digester and Fe-free digester. However, the methane production of ZVI + Fe₃O₄ added digester were 68.9% higher than Fe-free digester and 20.0% higher than ZVI-added digester, respectively. Sludge reduction rate of these three digesters also showed similar results. These indicated that hydrogenotrophic methanogenesis was not the main reason for methanogenesis in Fe₃O₄-added digester. Instead, Syntrophomonas and Methanosaeta were specially enriched in Fe₃O₄-added digesters, which implied that the potential DIET between Syntrophomonas and Methanosaeta was likely a crucial reason for accelerating anaerobic digestion of waste sludge.

Keywords: Anaerobic sludge digestion; Direct interspecies electron transfer; Fe(3)O(4); Hydrogen; Zero-valent iron.