Enhancement of methane production by Methanosarcina barkeri using Fe3O4 nanoparticles as iron sustained release agent

Abstract

Anaerobic digestion has attracted attention because it does not require power for aeration, it reduces excess sludge and it generates methane gas. However, the growth rate of anaerobic microorganisms is slow, resulting in low treatment efficiency. In this study, the impact of Fe3O4 nanoparticles (NPs) on the growth of methanogens, which is the rate-determining step in anaerobic digestion, was investigated using a pure culture of Methanosarcina barkeri as the model methanogen. M. barkeri were cultivated in iron free medium, as well as in media amended with various concentrations of Fe3O4 NPs with a mean diameter of 8.1 ± 2.4 nm. The production of methane gas was greatly increased when organisms were cultured in media containing NPs. After the methane production was saturated, methanol was newly added to the culture, which resulted in additional methane generation at a higher production rate than occurred during the initial round of cultivation in media containing 20 ppm Fe3O4 NPs. In addition, no evidence of negative impacts of Fe3O4 NPs on the growth of M. barkeri was observed. Taken together, these results strongly suggest that adding Fe3O4 NPs into the fermenter as an agent of sustained iron release can enable sustainable methane fermentation.