Abstract
The partial nitrification (PN) performance and the microbial community variations were evaluated in a sequencing batch reactor (SBR) for 172 days, with the stepwise elevation of ammonium concentration. Free ammonia (FA) and low dissolved oxygen inhibition of nitrite-oxidized bacteria (NOB) were used to achieve nitritation in the SBR. During the 172 days operation, the nitrogen loading rate of the SBR was finally raised to 3.6 kg N/m3/d corresponding the influent ammonium of 1500 mg/L, with the ammonium removal efficiency and nitrite accumulation rate were 94.12% and 83.54%, respectively, indicating that the syntrophic inhibition of FA and low dissolved oxygen contributed substantially to the stable nitrite accumulation. The results of the 16S rRNA high-throughput sequencing revealed that Nitrospira, the only nitrite-oxidizing bacteria in the system, were successively inhibited and eliminated, and the SBR reactor was dominated finally by Nitrosomonas, the ammonium-oxidizing bacteria, which had a relative abundance of 83%, indicating that the Nitrosomonas played the primary roles on the establishment and maintaining of nitritation. Followed by Nitrosomonas, Anaerolineae (7.02%) and Saprospira (1.86%) were the other mainly genera in the biomass.
Highlights
The partial nitrification (PN) performance and the microbial community variations were evaluated in a sequencing batch reactor (SBR) for 172 days, with the stepwise elevation of ammonium concentration
Several controlling factors can be applied to out-compete nitrite-oxidizing bacteria (NOB) and ensure nitrite accumulation, such as free ammonia (FA) or free nitrous acid (FNA) inhibition, dissolved oxygen (DO), pH, temperature and short sludge retention time (SRT)[6,7]
In phase I, during the first 7 days, the reactor was fed at low ammonium concentration (100 mg/L) and the ammonium nitrogen was primarily converted to nitrate rather than nitrite, suggesting that considerable levels of NOB were present in the reactor
Summary
As soon as the ammonium concentrations in the influent wastewater increased to 200 mg/L on day 8, nitrite accumulation occurred. From day 17 onwards, stable partial nitritation was maintained in the reactor, and the average NAR was 82%, indicating a steady inhibition of NOB by the strategy of limited aeration and high free ammonia[18]. In phase II, after the start-up period, the reactor was operated to elevate the NLR by increasing the influent ammonium concentration stepwise to test the PN performance at DO 0.8–1.0 mg/L. During this phase, the influent ammonium concentration was elevated to 300 mg/L, while the ammonium removal efficiency was maintained
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