Integration of denitrifying phosphorus removal via nitrite pathway, simultaneous nitritation–denitritation and anammox treating carbon-limited municipal sewage

• Achievement of nitritation was a prerequisite to improve nutrients removal.
• Denitrifying P removal via nitrite was the key pathway in anoxic zone.
• Simultaneous nitritation–denitritation contributed to N removal in aerobic zone.
• PCR verified presence of anammox bacteria with the largest of 1.32 × 106 copies/g VSS.
• Combining denitrifying P removal, SND with anammox to solve carbon-limited problem.

High nutrients removal above 90% from carbon-limited municipal sewage was obtained without adding external carbon source. Achieving nitritation was a prerequisite to improve nutrients removal. Denitrifying phosphorus (P) removal using nitrite as electron acceptor was the key pathway in anoxic zone, where nitrogen removal reached above 60% and average denitrifying P removal was 88%. Simultaneous nitritation/denitritation and anaerobic ammonia oxidation (anammox) possibly contributed to nitrogen removal of 26–36% in aerobic zone. Quantitative PCR assays presented that the abundance of anammox bacteria under nitritation was more than that under complete nitrification. The largest amount of anammox bacteria was 1.32 × 106 copies/g VSS, about 5.6 times increase over a period of 255 days. Nitrite concentration of 17 mg/L in aerobic zone inhibited anammox bacteria. Quantitative results suggested possible occurrence of anammox. Based on performance of nitritation, combining heterotrophic denitrification with autotrophic nitrogen removal is an effective strategy to improve nutrients removal from carbon-limited wastewater.