Niche Compartmentalization Promotes Dissolved Methane Removal and Simultaneous Nitrification and Denitrification in a Hybrid MABR

Here, we explore the potential of a hybrid membrane aerated biofilm reactor (MABR), where suspended biomass and a biofilm co-occur, to remove remnant concentrations of dissolved methane and ammonium in anaerobic effluents. A combination of long-term reactor operation, in situ batch tests, and 16S rRNA gene amplicon sequencing confirmed the coexistence and spatial arrangement of three microbial populations in this hybrid system. These three microbial populations include the coupling of aerobic methane-oxidizing bacteria, nitrifying bacteria, and denitrifying bacteria, which collectively were able to promote the removal of dissolved methane, a greenhouse gas, and the removal of ammonium present in anaerobically treated wastewater. Once steady-state operation was reached, the system demonstrated dissolved methane removal efficiency of 99% and simultaneous nitrification and denitrification with ammonium and total nitrogen removal efficiencies of 90 and 65%, respectively. Similarly, metaproteomics analysis under steady-state conditions showed expression patterns of key nitrogen- and methane-related enzymes at different zones of the hybrid MABR. Additionally, ¹⁵N tracer experiments revealed the production of ²⁹N₂, suggesting that nitrosation or nitrifier-denitrification processes may play an important role in the nitrogen loss when methane is the only organic carbon source added to the system. These results are useful for developing and optimizing strategies to mitigate greenhouse gas emissions and nitrogen-related issues in reclaimed water.