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, Mn₂O_3, 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 CH₄ 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.