Advanced nitrogen removal from low-strength municipal sewage by partial nitritation–anammox (PN-A) process: Zeolite-driven nitritation mechanism and microbial community analysis

The application of partial nitritation–anammox (PN-A) 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, contributing to maintain stable nitritation in zeolite sequencing batch reactor (ZSBR) during long-term operation (>170 days). The nitrite accumulation rate and nitrite production rate reached 96.8 ± 2.62 % and 0.42 ± 0.13 kgN/m 3 /d. Anammox process achieved a final effluent total inorganic nitrogen concentration below 7.0 mg/L and a total nitrogen removal efficiency of 82.68 %. 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 ( Thauera ), which synergized with anammox bacteria to increase nitrogen removal by 25.6 %. The findings present substantial potential for large-scale mainstream anammox treatment. • PN-A process for municipal wastewater treatment achieved high TINRE of 82.68 %. • Stabilized partial nitritation attributed to high FA environment driven by zeolite. • Denitrifying bacteria synergized with AOB and AnAOB to promote nitrogen removal. • Elevating FA could recover PN system from deterioration in municipal wastewater.