Enhancement of methane production from anaerobic digestion using different manganese species

The enhancement of methane (CH4) production by metal addition during anaerobic digestion (AD) of organic waste has drawn much attention in recent years. In this study, four different forms of manganese (Mn, MnO, Mn2O3 and MnO2) were applied at the beginning of AD to investigate their effects on CH4 production. Results suggested that both Mn and the three manganese oxides accelerated CH generation. Mn and MnO showed thehigheset carbon conversion rates (about 67%) but the Mn group generated more CH4 (330 mL g(-1) VS) than MnO. Moreover, the duration of lag phases for CH4 production was in the following order: MnO Mn < MnO2 < Mn2O3. Promotion effect of manganese on AD process was found to be the result of a composite overlay: (1) initial valence of manganese (IVM) was more likely to impact on bacteria than archaea, and high IVM could be toxic to most bacteria, (2) a high Mn2+ concentration will be unfavorable to interspecies electron transfer, and the toxicity of Mn2+ to some dominated archaea (e.g. genus Methanosarcina) could improve the competitiveness of other archaea, thereby improved the biodiversity of the archaea.