Mainstream nitrogen separation and side-stream removal to reduce discharge and footprint of wastewater treatment plants

The activated sludge process is efficient for pollutant removal, but was criticized for its large upfront investment and land area requirements. Improving nitrogen removal to levels sufficient to reduce eutrophication is a challenge to conventional nitrification and denitrification, which is limited by process configuration (with nitrate recirculation) and environmental inhibition. To satisfy stringent discharge standards within a compact plant footprint, a sustainable strategy by moving nitrogen removal from mainstream to side-stream is designed by a cycle of ammonium exchange, regeneration and nitrogen removal (AERN), combined with biological and physiochemical technologies. Ammonium was rapidly captured by ion exchangers, then exchanged into regenerant, and converted to N₂ by chlorination or Sharon-anaerobic ammonia oxidation in the side-stream. The AERN cycle can be combined with a high-rate anaerobic/aerobic process and chemical phosphorus removal to construct a HAERN process, or inserted between a coagulation-sedimentation tank and a membrane bioreactor to construct a CAERNM process. Two AERN-based systems both achieved efficient pollutants removal (especially for nitrogen removal of 86.8–93.7%) in long-term running, and didn't impair exchange capacity and properties of ion exchangers. Compared with the conventional anaerobic/anoxic/aerobic process, AERN-based processes reduce land occupancy, upfront investments, and treatment costs by 59.9–71.1%, 25.5–38.0% and 2.3–31.0%, respectively.