[Competitive Selection of Hydroxylamine on Ammonia Oxidizing Bacteria and Nitrite Oxidizing Bacteria]

The effective inhibition of nitrite oxidizing bacteria (NOB) is the key to realizing satisfactory nitrite accumulation and achieving effective nitritation. In order to explore the selective effect of hydroxylamine (NH₂ OH) on ammonia oxidizing bacteria (AOB) and NOB, a sequencing batch reactor (SBR) with the operation mode of anaerobic/aerobic/anoxia (A/O/A) was used to observe the start-up of nitritation at different concentrations and frequencies of NH₂ OH. The results showed that when 5 mg·L^-1 of NH₂ OH was added once every 2 cycles, the nitrite accumulation rate (NAR) increased from 0.1% to 57.4% in 6 days, and was maintained at (62.0±4.6)% until the end of the trials. In the typical cycle on day 6, the NN₄⁺-N dropped from 26.05 mg·L^-1 to 8.06 mg·L^-1, thus producing 9.02 mg·L^-1 of NO₂^--N and 6.70 mg·L^-1 of NO₃^--N. Meanwhile, the ratio of the maximum activity of AOB (rAOB) to NOB (rNOB) increased from 1.05 on day 1 to 4.22 on day 9. Moreover, qPCR results indicated that the abundance of AOB and NOB decreased to 30.2% and 19.1%, respectively, on day 9 in comparison to the original sample. The results indicate that the selective effect of AOB and NOB based on NH₂ OH is expected to provide a feasible application for the rapid start-up nitritation of municipal wastewater.