Advanced nitrogen removal of low C/N ratio sewage in an anaerobic/aerobic/anoxic process through enhanced post-endogenous denitrification

Currently, it is a major challenge for waste water treatment plants (WWTPs) to achieve enhanced nitrogen removal economically and effectively from carbon-limited sewage to meet gradually stringent discharge quality standards. Enhanced nitrogen removal can be achieved by endogenous denitrification (ED) treatment of low C/N municipal sewage, but its application is limited by the slow reaction rate. In this study, a novel process of Sludge Double Recirculation-Anaerobic/Aerobic/Anoxic (SDR-AOA) was developed to improve nitrogen removal efficiency via ED. ED was successfully enhanced by an extra sludge recirculation to post-anoxic zone and the denitrification rate increased from 0.1 to 0.17 kgN/(m(3).d). Moreover, the pre-anaerobic zone enhanced the intracellular carbon storage, which might also favor the ED process. Overall, under an influent C/N of 2.67, nitrogen removal efficiency of 97.7% was achieved with effluent total inorganic nitrogen (TIN) of 1.56 +/- 1.77 mg/L and nitrogen removal rate (NRR) of 0.14 kgN/(m(3).d). Therefore, this study provides a convenient approach to improve the nitrogen removal efficiency of municipal sewage with low C/N. (C) 2020 Elsevier Ltd. All rights reserved.