Iron-material-facilitated methane production from anaerobic wastewater treatment

Various iron materials have been used to improve the methane production rate in anaerobic sludge. The effects of iron materials, including zerovalent iron (ZVI), magnetite (iron (II,III) oxide (Fe3O4)) and iron (III) oxide (Fe2O3), on the methane production rate were compared. It was found that all the iron materials could improve the methane production rate, and ZVI, iron (II,III) oxide and iron (III) oxide increased the methane production rate by 19.8, 13.7 and 17.9%, respectively, in which ZVI performed best in improving methane production. Then, the long-term effects of ZVI on the methane production rate of anaerobic organisms were further studied. ZVI increased the methane production rate by 7.2%. The improvement was unstable and decreased due to corrosion and loss of ZVI in the anaerobic wastewater-treatment system. The improved performance was recovered after ZVI was re-added into the anaerobic sludge; the methane production rate increased by 6.1%. The added ZVI obviously enriched the exoelectrogenic archaea Methanobacterium due to its ability of direct interspecific electron transfer, and the relative abundance of Methanobacterium was up to 61.99%. Enhanced direct interspecific electron transfer was revealed as the main mechanism involved in enhanced methanogenesis in anaerobic sludge.