Nitrogen-associated niche characteristics and bacterial community estimated by ¹⁵N-DNA-stable isotope probing in one-stage partial nitritation/anammox process with different ammonium loading

Anaerobic ammonium oxidation coupled with partial nitritation is critical for cleaner production in sewage treatment. The long-term effects of high- and low-strength influent ammonium (NH₄⁺-N) on the anammox activity, ecological niche characteristics and active microbial community were investigated in a one-stage partial nitritation/anammox (PN/A) process. The total nitrogen (TN) removal efficiency was up to 90% with influent NH₄⁺-N of 192 mg/L. The ¹⁵N-isotope pairing technique illustrated that the potential anammox rate could reach to 3507.8 nmoL/g-sludge/h, accounting for 73.2% of dinitrogen production. As the influent NH₄⁺-N decreased to 63 mg/L, the anammox population significantly decreased and the Nitrospira became the dominant specialized species in the PN/A system. The Nitrobacter had the smallest niche overlap value and the furthest ecological distance to the anammox bacteria among the seven investigated nitrogen conversion-related genes along the influent NH₄⁺-N concentration gradient, indicating different ecological similarities. The redundancy analysis showed that the rise of dissolved oxygen caused by low NH₄⁺-N might be the main cause of the excessive proliferation of the Nitrospira. The ¹⁵N-DNA-stable isotope probing illustrated that both the class Anaerolineae and Proteobacteria had closely symbiotic relations with the Planctomycetacia in this in situ surveys. This study provides a deep understanding of PN/A process treating low-ammonium mainstream wastewater from the viewpoint of microecology.