Advanced nitrogen removal from low-strength municipal sewage by partial nitritation/anammox process: Zeolite-driven nitritation mechanism and microbial community analysis

The application of partial nitritation/anammox process for treating low-strength municipal sewage remains challenging due to the instability nitrite accumulation. This study proposed a zeolite-assisted nitritation strategy to achieve stable nitrite supply in municipal sewage treatment, followed by an integrated anammox process for further nitrogen removal. The results demonstrated that substantial ammonium adsorption by zeolite created an enrichment zone, in which the adsorbed ammonium was 3.8-55 times that of free ammonium. The enrichment zone inside the zeolite and the high FA concentration of the solution jointly inhibited NOB activity, coutributing to maintain stable nitritation in zeolite sequencing batch reactor during long-term operation. High-throughput sequencing revealed persistent suppression of Nitrospira activity, while Nitrosomonas was the dominant genus in the nitritation unit. Candidatus Brocadia and Candidatus Kuenenia were recognized as the primary functional bacteria responsible for nitrogen removal in the anammox unit. The carbon source in the actual municipal sewage facilitated the growth of denitrifying bacteria, which synergized with anammox bacteria to increase nitrogen removal by 25.6 %. The findings present substantial potential for large-scale mainstream anammox treatment.