Dual regulation of microbial denitrification and methane mitigation with manganese-humic chelates

Methane emissions pose a significant environmental threat, as they contribute significantly to global climate change. During the conventional denitrification process, the demand for exogenous organic carbon and anoxic conditions can favor methanogenesis. The incorporation of transition metal manganese may supplant organic carbon as electron donor in conventional denitrification procedures, which may impede methanogenesis theoretically. The study explored the inhibitory effects of manganese, introduced as manganese-humus chelates (Mn-HA), on methanogenesis in manganese-driven nitrification and denitrification sludge. By Gompertz model fitting and Metagenomic analysis, a significant reduction in methanogenesis was observed, which is manifested by an extended methanogenic lag time λ and a diminished potential methanogenic content Pm. In the nitrogen removal experiment, Mn²⁺ may substitute for COD in manganese autotrophic denitrification, resulting in the removal of nitrate. The generated high-valence manganese may replace part of the dissolved oxygen (DO) for manganese-mediated ammonia oxidation (Mnammox), leading to the removal of more ammonium.