Anaerobic technologies have been proposed as a promising solution to enhance bioenergy recovery and to transform a wastewater treatment plant (WWTP) from an energy consumer to an energy exporter. However, 20-60% of the methane produced remains dissolved in the anaerobically treated effluent, which is a potent greenhouse gas and is easily stripped out in the aeration tank. This study aims to develop a solution using dissolved methane to support denitrification, thus simultaneously enhancing nitrogen removal and achieving beneficial use of dissolved methane. By coupling anaerobic ammonium oxidation (anammox) with nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO), up to 85% of dissolved methane and more than 99% of nitrogen were removed in parallel in a biofilm system. Mass balance was conducted during both long-term operation and short-term batch tests, which indicated that n-DAMO bacteria and n-DAMO archaea indeed contributed jointly to the methane removal. The 16S rRNA gene amplicon sequencing further showed the co-presence of n-DAMO bacteria and n-DAMO archaea, while anammox bacteria were detected with a low relative abundance. This proposed technology can potentially be applied to reduce the carbon footprint and to save the organic carbon consumption in WWTPs.