Toward energy-neutral wastewater treatment: A membrane combined process of anaerobic digestion and nitritation–anammox for biogas recovery and nitrogen removal

• Combined process was developed by treating concentrated municipal wastewater under ambient temperature.
• The process was suitable for start-up of the anaerobic digestion and nitritation–anammox.
• The process presented a stable removal performance for nitrogen and COD associated with stable methane production.
• The net energy consumption estimated of combined process was 0.09 kWh/m3.

Energy-neutral wastewater treatment is increasingly emphasized in practice. In this study, a membrane combined process of a submerged anaerobic MBR and CANON MBR was investigated for biogas recovery and nitrogen removal by treating membrane concentrated municipal wastewater under ambient temperatures. Anaerobic digestion and nitritation–anammox were successfully started up in MBRs within a shorter period. During the sequential operation of 81 d, the COD removal efficiency of the whole system was about 96% and most CODs were converted into biogas in the anaerobic MBR with a stable methane yield of 1672 mL/d, corresponding to 223 mL CH4/g COD. Meanwhile nitrogen removal was obtained in the sequential CANON MBR with a total nitrogen removal efficiency of 81%. Furthermore, the net energy consumption estimated of membrane combined process was 0.09 kWh/m3. These results indicated that the membrane combined process is a promising treatment process to achieve energy-neutral municipal wastewater treatment.