Nitrogen removal from wastewater: A comprehensive review of biological nitrogen removal processes, critical operation parameters and bioreactor design

The nitrogenous compounds present in wastewaters create severe biotic stress and alter the biodiversity when discharged into aquatic ecosystems. Biological nitrogen removal (BNR) encompassing well-established and emerging technologies offer an effective process for removal of nitrogen from wastewater and side-streams. The present study provides a comprehensive review of BNR based technologies that include conventional N/DN, PN-ANAMMOX, and simultaneous deammonification and denitrification. In addition to detailed mechanisms, this study covers bioreactor configurations, operational parameters, efficacies, and process control strategies. Furthermore, recent developments, key prospects, challenges, and ongoing research trends are discussed. The economic aspects of BNR processes have been scarcely reported in the literature; thus, this review also includes the life-cycle assessment of BNR processes to ascertain the feasibility for wastewater treatment plants of different capacity. This review will be beneficial to researchers and practitioners in improving the performance of current BNR systems to develop sustainable and cost-effective nitrogen removal processes for wastewater treatment.