Partial nitrification response to dissolved oxygen variation and aerobic starvation: Kinetics and microbial community analyses

Partial nitrification (PN) has great significance in promoting both anaerobic ammonium oxidation (anammox) and advanced nitrogen removal. However, the kinetics of PN have not been sufficiently studied. Deterioration of PN often occurs due to nitrite-oxidizing bacteria (NOB) outgrowth, for which the dissolved oxygen (DO) is a critical factor. This study investigated the kinetic parameters of ammonia-oxidizing bacteria (AOB) and NOB by varying the DO concentration. The partial nitrification-anammox (PNA) process was operated under sequentially low (0.3–0.8 mg/L) and high (4.0–5.0 mg/L) DO. The results show that AOB could not adapt to low DO, resulting in a significant decrease in the maximum AOB activity (Vmax,AOB) and a slightly altered oxygen half-saturation constant of AOB (KO,AOB). Conversely, KO,NOB decreased and Vmax,NOB maintained, indicating that the main NOB genus, Nitrospira, was more adaptable to DO changes. Under high DO, AOB growth was weaker than NOB, leading to a low Vmax,AOB – Vmax,NOB value; KO,AOB increased and was larger than KO,NOB and PNA was eventually destroyed. The aerobic starvation was then adopted to restore PN. AOB recovered faster and dominated, with Vmax,AOB greatly exceeding Vmax,NOB. Finally, NOB were inhibited and PN was recovered. During this process, KO,NOB increased and was higher than KO,AOB. Changes in the kinetic parameters, especially the Vmax,AOB -Vmax,NOB value, have specific guiding significance for DO regulation during PNA. This work helps better understand the effect of DO variations on the nitrifying microbial community, which influences oxygen affinity and maximum activity.