Resilience of anammox application from sidestream to mainstream: A combined system coupling denitrification, partial nitritation and partial denitrification with anammox

[Display omitted] •Key technical bottlenecks of mainstream anammox application are summarized.•Stable supply of nitrite, dominance of AnAOB are the key issues.•PN and PD are the suppliers of nitrite, while anammox and DN are the producers of N2.•A CBNR system based on PANDA process is proposed to improve resilience of mainstream anammox. Anaerobic ammonium oxidation (anammox) is a potential process to achieve the neutralization of energy and carbon. Due to the low temperature and variation of municipal sewage, the application of mainstream anammox is hard to be implemented. For spreading mainstream anammox in practice, several key issues and bottlenecks including the start-up, stable NO2–-N supply, maintenance and dominance of AnAOB with high activity, prevention of NO3–-N buildup, reduction of sludge loss, adaption to the seasonal temperature and alleviation of COD impacts on AnAOB are discussed and summarized in this review in order to improve its startup, stable operation and resilience of mainstream anammox. Hence a combined biological nitrogen removal (CBNR) system based on conventional denitrification, shortcut nitrification–denitrification, Partial Nitritation and partial Denitrification combined Anammox (PANDA) process through the management of organic matter and nitrate is proposed correspondingly aiming at adaptation to the variations of seasonal temperature and pollutants in influent.