Up-concentration of nitrogen from domestic wastewater: A sustainable strategy from removal to recovery

Improving environmental quality and achieving a circular economy require developing wastewater resource recovery facilities (WRRFs) under stringent discharge standards. As a sustainable alternative to control nitrogenous pollution, nitrogen separation and recovery from wastewater is the bottleneck to break through in WRRFs and is critical to alleviating anthropogenic interference with the global nitrogen cycle. However, nitrogen from low-strength domestic wastewater (20-50 mg/L) is overlooked and requires up-concentration for adequate recovery. This review overviewed the advances and significant challenges of current nitrogen removal and recovery methods. Then several nitrogen up-concentration technologies were summarized to clarify their working location, technical performances, influential factors, and strategies for nitrogen recovery from concentrate. The pretreatment and post-treatment technologies were reviewed and discussed to improve the adaptabilities of these up-concentration technologies in WRRFs. Considering the coexistence of NH4+ with impurities or high salinity in the up-concentration process, a novel workflow for nitrogen recovery by coupling up-concentration with a targeted conversion process was proposed to reach the high up-concentration factor, satisfy stringent discharge standards, and harvest valuable products. The results anticipated a possible effective and sustainable layout for WRRFs via combining nitrogen up-concentration with carbon capture and phosphorus enrichment.