Enhanced simultaneous nitrogen and phosphorus removal from low COD/TIN domestic wastewater through nitritation-denitritation coupling improved anammox process with an optimal Anaerobic/Oxic/Anoxic strategy.

Advanced nitrogen and phosphorus removal in a single-stage suspending-sludge system was achieved by employing a novel Anaerobic/Oxic/Anoxic (AOA) strategy over 200 days. Satisfactory total inorganic nitrogen (TIN) removal efficiency of 90.4% was achieved and effluent phosphorus was below 0.5 mg/L when treating domestic wastewater with the chemical oxygen demand (COD)/TIN as low as 2.98 ± 1.26. Stable nitritation was maintained with the ammonia residual and low dissolved oxygen of 0.2-0.5 mg/L at aerobic stage following by a post anoxic stage. The much higher activity of ammonia oxidation bacteria (12.99 mgN/gVSS/h) was achieved than the nitrite oxidation bacteria (0.09 mgN/gVSS/h). Notably, improved anammox performance was obtained without initial inoculation, contributing 47.4% to TIN removal. The abundance of Nitrosomonas increased from 0.12% to 0.95% (P < 0.001) and self-enrichment of anammox bacteria Ca. Brocadia was confirmed. It provided new insight into the advanced nutrient removal with comprehensible regulation and less aeration requirement.