Important amounts of dissolved methane are found in the liquid fraction of digestates originated in wastewater treatment plants (WWTP) with biogas production. If not treated properly, this potent greenhouse gas can be desorbed and emitted into the atmosphere. The anaerobic oxidation of methane coupled to denitrification (N-AOM) represents an innovative microbial process for preventing these emissions. In N-AOM-based technologies, methane can be removed before desorption parallel to the elimination of nitrogenous pollutants such as nitrate. Nitrate serves as the terminal electron acceptor for microorganisms to achieve methane oxidation to carbon dioxide under strictly anoxic conditions. For its application in WWTP, N-AOM must be studied under relevant conditions in WWTP such as continuous operation and adequate hydraulic retention times (HRT). In this study, a continuous stirred-tank reactor (CSTR) inoculated with a mixture of enriched biomass from local wastewater treatment facilities was operated for 35 days at an HRT of 17 h and a gas retention time (GRT) of 0.98 h under rigorous anaerobic conditions. Realistic N-NO3- loads of 43 g N-NO3- m-3 h-1 were applied and resulted in a rapid startup of the process of 7 days and average methane elimination capacities of 24.4 ± 8.6 g CH4 m-3 h-1. Moreover, average nitrate removal rates of 12 ± 4.3 g N-NO3- m-3 h-1 were observed in parallel to methane consumption. The results inhere presented indicate that high methane and nitrate elimination capacities can be achieved under relevant conditions found in WWTPs under a continuous regime. These results open novel research avenues that could aid in the development of N-AOM-based technologies resulting in the diminishment of the environmental impact of wastewater treatment.

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