Achieving High-LevelNitrogen Removal Performancefor Unstable Partial Nitrification Effluent through Endogenous DissimilatoryNitrate Reduction to Ammonium Function of Anammox Bacteria

The combination of partial nitrification (PN) and anammox (PN-anammox) was the mainstream technology for carbon-deficient and ammonium-rich wastewater treatment. Nevertheless, the stable operation of the PN-anammox process has always faced significant challenges including unstable nitrite (NO₂^–) accumulation and nitrate (NO₃^–) generation. In this paper, it was first presented that NO₃^– and ammonium (NH₄⁺) could simultaneously be degraded by anammox bacteria via an endogenous dissimilatory nitrate reduction to ammonium (DNRA) pathway followed by a traditional anammox reaction. The transmission electron microscopy images and the inhibition experiments results of penicillin G and iodoacetic acid suggested that the intracellular carbon (glycogen) inside anammox bacteria supplied electrons for this endogenous DNRA conversion of NO₃^–. The isotope experiments further demonstrated that the full endogenous DNRA transformation of NO₃^– was synchronized even in the presence of external NH₄⁺. Based on this method, a PN-anammox system was established, and a high total nitrogen removal performance (95.50%∼100.00%) was achieved even with an unstable PN process. Our work further displayed the complex nitrogen metabolic mechanism of anammox bacteria, the obstacles in the PN-anammox process could be solved by relying on the endogenous DNRA function in anammox bacteria.