Simultaneous removal of methane and high nitrite from the wastewater by Methylomonas sp. with soluble methane...

Aerobic methanotrophs play a crucial role in controlling methane emission in wastewater treatment. However, the high nitrite produced during ammonium oxidation, nitrate assimilation, and denitrification hinders methane oxidation and nitrogen removal. In this study, Methylomonas sp. HYX-M1, possessing two methane monooxygenase and multiple nitrite reductase genes, demonstrated efficient methane oxidation, coupled with nitrite removal abilities up to 6 mM. Strain HYX-M1 presented methane oxidation rate of 0.05 mmol/d and nitrite removal rate of 0.53 mM/d under low-oxygen conditions. Assimilation and denitrification mainly accounted for 94.6-96.06 % and 3.10-5.03 % of nitrite removal. Methane monooxygenase genes, pmoA and mmoX expressed in different nitrite concentrations. Meanwhile, the nirB and nirD of strain HYX-M1 upregulated by 2.7- and 8.5-fold in 6 mM, respectively. The sod and ahpC genes upregulated, contributing to the survival of strain HYX-M1 in high nitrite. These findings provide a new strategy for the application of aerobic methanotrophs in regulating methane emission of wastewater with high nitrite.