Nitrogen recovery from wastewater as nitrate by coupling mainstream ammonium separation with side stream cyclic up-concentration and targeted conversion

A sustainable strategy to recover nitrogen as nitrate by ammonium ion exchange and regeneration (AIR) from low-strength domestic wastewater was proposed to reduce nitrogenous pollutants discharge and alleviate nitrogen loss from atmosphere. In the AIR module, ammonium is rapidly swapped by ion exchangers from the wastewater, and then converted and concentrated as nitrate by cyclic regeneration and side stream nitrification. Nitrate is further concentrated by electrodialysis, and recovered as NaNO₃. Then chemically enhanced primary treatment, AIR and membrane bioreactor were coupled to construct an efficient and compact Chemically enhanced primary treatment - Ammonium Ion exchange and Regeneration - Membrane bioreactors (CAIRM) process for nitrogen recovery and synchronous pollutants removal from domestic wastewater under stringent discharge standards. Pilot-scale CAIRM efficiently removed pollutants (nitrogen removal of 93.7%) and recovered 77.1% ammonium during long-term operation without damage to performance of ion exchangers. Compared with the anaerobic/anoxic/aerobic process, CAIRM process reduced land occupancy by 70.1%, decreased upfront investment and treatment cost by 29.3% and 40.7% after resource recovery, and cut greenhouse gas emission by 52.5%. Application of the proposed strategy is expected to save energy of nitrate production and convert global nitrogen circular pollution to circular economy.