Reduction of greenhouse gases emissions during anoxic wastewater treatment by strengthening nitrite-dependent anaerobic methane oxidation process

•Co-existence of n-damo bacteria and methanogens was achieved by using UASB.•Introduction of n-damo process in anoxic environment could reduce GHG emissions.•Carbon source had significant influence on diversity of n-damo bacteria.•In situ production and consumption of CH4 led to unique n-damo bacteria community.

Nitrite-dependent anaerobic methane oxidation (n-damo) is a recently discovered process performed by NC10 phylum, which plays an important role in greenhouse gases (GHG) reduction. In this study, co-existence of n-damo bacteria and methanogens was successfully achieved by using upflow anaerobic sludge blanket (UASB) reactor. Reactor with inorganic carbon source (CO2/H2) showed the highest abundance of n-damo bacteria and the highest n-damo potential activity, resulted in its highest nitrogen removal rate. Significant reduction in GHG was obtained after introduction of n-damo process, especially for N2O. Furthermore, GHG emissions decreased with the increase of n-damo bacteria abundance. Community structure analysis found carbon source could influence the diversity of n-damo bacteria indirectly. And phylogenetic analysis showed that all the obtained sequences were assigned to group B, mainly due to in situ production and consumption of CH4.