Achieving High-Level Nitrogen Removal Performance for Unstable Partial Nitrification Effluent through Endogenous Dissimilatory Nitrate 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.