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The mainstream anaerobic ammonium oxidation (anammox) process provides strong support to the on-going paradigm shift from energy-negative to energy-neutral in wastewater treatment plants. However, the low temperature (e.g., below 15 °C) represents one of the major challenges for mainstream anammox in practice. In this study, a stable nitrogen removal rate (0.13 kg m–3 day–1), together with a high-level effluent quality (<5.0 mg N L–1), was achieved in a lab-scale upflow membrane biofilm reactor (MBfR) by coupling anammox with nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) microorganisms, at a temperature as low as 10 °C. With the temperature being progressively decreased from 25 to 10 °C, the total nitrogen removal efficiency was maintained in the range of 90–94% at a constant hydraulic retention time of 9 h. The impact of temperature on the biofilm system coupling anammox and n-DAMO reactions increased at a lower temperature range with higher Arrhenius coefficients. Additionally, 16S rRNA gene sequencing results showed that anammox bacteria, n-DAMO bacteria, and n-DAMO archaea jointly dominated the biofilm, and their respective abundances remained relatively stable when the temperature was decreased. The major reason for this temperature-tolerated performance is the overcapacity developed, which is indicated by biofilm thickness measurements and mathematical modeling. The stable performance obtained in this study shows promise for the n-DAMO application in domestic wastewater.

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.

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