Dynamic pH regulation drives Nitrosomonas for high-rate stable acidic partial nitritation

Abstract

How to intensify the ammonia oxidation rate (AOR) is still a bottleneck impeding the technology development for the innovative acidic partial nitritation because the eosinophilic ammonia-oxidizing bacteria (AOB), such as Nitrosoglobus or Nitrosospira, were inhibited by the high-level free nitrous acid (FNA) accumulation in acidic environments. In this study, an innovative approach of dynamic acidic pH regulation control strategy was proposed to realize high-rate acidic partial nitritation driven by common AOB genus Nitrosomonas. The acidic partial nitrification process was carried out in a laboratory-scale sequencing batch moving bed biofilm reactor (SBMBBR) for long-term (700 days) to track the effect of dynamic acidic pH on nitrifying bacterial activity. The results indicated that the influent NH₄⁺-N concentration was about 100 mg/L, the nitrite accumulation ratio was exceeding 90%, and the maximum AOR can reach 14.5 ± 2.6 mg N L^-1h^-1. Although the half-saturation inhibition constant of NOB (K_{I_FNA(AOB)}) reached 0.37 ± 0.10 mg HNO₂N/L and showed extreme adaptability in FNA, the inactivation effect of FNA (6.1 mg HNO₂N/L) for NOB was much greater than that of AOB, with inactivation rates of 0.61 ± 0.08 h^-1 and 0.06 ± 0.01 h^-1, respectively. The effluent pH was gradually reduced to 4.5 by ammonia oxidation process and the periodic FNA concentration reached 6.5 mg HNO₂N/L to inactivate nitrite-oxidizing bacteria (NOB) without negatively affecting Nitrosomonas during long-term operation. This result provides new insights for the future implementation of high-rate stabilized acidic partial nitritation by Nitrosomonas.

Keywords: High-rate acidic partial nitritation; Nitrosomonas; dynamic acidic regulation.