The role and related microbial processes of Mn-dependent anaerobic methane oxidation in reducing methane emissions from constructed wetland-microbial fuel cell

Abstract

Anaerobic oxidation of methane (AOM) plays an important role in global carbon cycle and greenhouse gas emission reduction. In this study, an effective green technology to reduce methane emissions was proposed by introducing Mn-dependent anaerobic oxidation of methane (Mn-AOM) and microbial fuel cell (MFC) technology into constructed wetland (CW). The results indicate that the combination of biological methods and bioelectrochemical methods can more effectively control the methane emission from CW than the reported methods. The role of dissimilated metal reduction in methane control in CW and the biochemical process associated with Mn-AOM were also investigated. The results demonstrated that using Mn ore as the matrix and operating MFC effectively reduced methane emissions from CW, and higher COD removal rate was obtained in CW-MFC (Mn) during the 200 days of operation. Methane emission from CW-MFC (Mn) (53.76 mg/m²/h) was 55.61% lower than that of CW (121.12 mg/m²/h). The highest COD removal rate (99.85%) in CW-MFC (Mn) was obtained. As the dissimilative metal-reducing microorganisms, Geobacter (5.10%) was found enriched in CW-MFC (Mn). The results also showed that the presence of Mn ore was beneficial to the biodiversity of CW-MFCs and the growth of electrochemically active bacteria (EAB) including Proteobacteria (35.32%), Actinobacteria (2.38%) and Acidobacteria (2.06%), while the growth of hydrogenotrophic methanogens Methanobacterium was effectively inhibited. This study proposed an effective way to reduce methane from CW. It also provided reference for low carbon technology of wastewater treatment.

Keywords: Anaerobic oxidation of methane; Biochemical process; CW-MFC; Dissimilatory manganese reduction; Methane control.