Advanced nitrogen removal from extremely low carbon/nitrogen ratio municipal wastewater by optimizing multiple pathways based on step-feed and intermittent aeration.

The advantages of step-feed and intermittent aeration have been well-documented, however, combining them to enhance nitrogen removal in anaerobic/oxic/anoxic systems has been rarely explored. This study established the non-single-form anoxic stages by step-feed and intermittent aeration and finally enhanced the nitrogen removal of real municipal wastewater with step-feed anaerobic/oxic/anoxic/oxic/anoxic operation mode. Results revealed that Candidatus_Brocadia increased from 0.00 % to 0.21 % in the suspended sludge system, contributing 54.7 % of the nitrogen removal. Partial nitrification (PN) and endogenous partial denitrification (EPD) supplied nitrite for Anammox. A comprehensive multi-pathway nitrogen removal system, encompassing PN, nitrification, partial denitrification, Anammox, EPD/Anammox, and denitrification was constructed. The system effectively reduced total inorganic nitrogen concentration to 3.6 ± 1.2 mg/L at a carbon/nitrogen ratio of 3.0 ± 0.3, achieving a nitrogen removal efficiency of 95.3 ± 1.5 %. This study provides a novel approach for the advanced treatment of municipal wastewater and enrichment of anaerobic ammonia-oxidizing bacteria.