Anaerobic oxidation of methane (AOM) driven by multiple electron acceptors in constructed wetland and the related mechanisms of carbon, nitrogen, sulfur cycles

Anaerobic oxidation of methane (AOM) mediated by microorganisms plays an important role in the global carbon cycle and methane emission control. This study demonstrated that simultaneous multi-electron acceptor-driven AOM existed in the electroactive constructed wetland environment of freshwater, which is crucial to global carbon, sulfur, nitrogen cycles and the manganese, iron, humics reduction. This biochemical process was mediated by two anaerobic methanotrophic archaea (ANME) jointly, ANME-2a and ANME-2d. Better removal efficiency of sulfate (45.65±3.47%), ammonium nitrogen (96.48±3.82%) and COD (94.83±5.89%) was observed in CW-MFC with AOM driven by multi-electron acceptor (CW-MFC_Mn). In addition, the methane emissions from CW-MFC with sulfate and nitrogen dependent AOM were reduced by 57.50% in presence of manganese ore, suggesting that multi-electron acceptors-driven AOM can effectively control methane emissions. The transformation of manganese oxide in wetland manganese ore was studied, and almost no Mn (Ⅱ) residue was detected in the effluent, indicating the potential role of Mn-dependent AOM in manganese pollution removal. This study also revealed the interactions of methanogenesis, electrogenesis, multi-electron acceptor-driven AOM and dissimilatory metal reduction (DMR) involved in CW-MFC, in which Geobacter played a crucial role in the association of various biological reactions. This study not only expands the understanding of AOM in nature, but also proposed a novel sight to simultaneously control wetland methane emissions, manganese, sulfur, and nitrogen pollution.