Recent advances of partial anammox by controlling nitrite supply in mainstream wastewater treatment through step-feed mode

At present, the step-feed process is a very active branch in practical application of mainstream wastewater treatment, and the anammox technology empowers the sustainable development and in-depth research of step-feed process. This review provides a systematically inspection of the realization and application of partial anammox process through step-feed mode, with a particular focus on controlling nitrite supply for anammox. The characteristics and advantages of step-feed mode in traditional management are reviewed. The unique organics utilization strategy by step-feed and indispensable intermittent aeration mode creates advantages for achieving nitritation (NH4+ → NO2−) and denitratation (NO3− → NO2−), providing flexible combination possibility with anammox. Additionally, the lab- or pilot-scale control strategies with different forms of anammox, including nitritation/anammox, denitratation/anammox, and double-anammox (combined nitritation/anammox and denitratation/anammox), are summarized. Finally, future directions and application perspectives on leveraging the relationship between flocs and biofilm, nitritation and denitratation, and different strains to maximize the anammox proportion in N-removal are proposed.