Anammox-based technologies for municipal sewage nitrogen removal: Advances in implementation strategies and existing obstacles

Anaerobic ammonia oxidation (anammox) is one of the most promising novel biotechnology for municipal sewage nitrogen (N) removal. Nonetheless, the full-scale application of the mainstream anammox process in municipal sewage treatment is limited owing to critical nitrite supply is easily susceptible to environmental conditions. Presently, partial-nitrification (PN) and partial-denitrification (PD) are existing two nitrite-generating pathways for anammox, while operating stability and optimizing regulation have been outstanding issues. Hence, a comprehensive summary of the potential ventures and control procedures to overcome these challenges is pivotal to facilitating the development and application of anammox in municipal sewage treatment. Based on the anammox reaction mechanism, this review summarizes the operating regulation strategies of PN coupled anammox (PN/A) and PD coupled anammox (PD/A) for treating municipal sewage. In addition, different anammox-based technical models aim to enhance the N-removal performance for municipal sewage were described, and the bottleneck problems that hinder the realization of anammox treating municipal sewage were summarized from engineering application perspective. A novel anaerobic/aerobic/anoxic (AOA) process for advanced N-removal from low C/N municipal sewage by combining partial nitrification-endogenous partial denitrification coupling anammox (PN(E_n)PD/A) was innovatively proposed, and its feasibility and N conversion route in efficient N-removal was analyzed. Meanwhile, the N-removal performance, consumption reduction and emission reduction effect, process characteristics and application scenarios of PN/A and PD/A were compared and analyzed. Finally, the research directions of anammox in mainstream sewage treatment were summarized and prospected in order to provide reference for the transformation of domestic sewage treatment process to anammox.