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The effective inhibition or wash-out of nitrite oxidizing bacteria (NOB) is the key challenge for the application of partial nitritation/anammox (PA/N) process in domestic wastewater treatment. The deteriorated domestic wastewater PN/A system was used to investigate the recovery effect of hydroxylamine (NH2OH) concentration and dosing mode on it. The nitrate (NO3 --N) production ratio of the PN/A system was 0.90, which was due to the overgrowth of NOB. The results showed that when the initial NH2OH concentration was 10mg/L in the sequencing batch reactor (SBR) and NH2OH was added once a day, the ratio of NO3 --Nproducted/NH4 +-Nconsumed was decreased from 0.90 to 0.11 after adding NH2OH for 20d. It indicated that NH2OH (10mg/L) addition could restore PN/A process in-situ. The ratio of NO3 --Nproducted/NH4 +-Nconsumed increased to 0.15 again after stopping NH2OH addition for 59d. When continued to add NH2OH into reactor for 5d, the PN/A process operated well. Therefore, the intermittent addition of NH2OH strategy could maintain the stable performance of the PN/A process. The real-time quantitative PCR results showed that the NOB abundance was decreased continuously from (4.52±0.44)×1010copies/g VSS (Day 6) to (2.30±0.80)×109copies/g VSS (Day 157) after NH2OH (10mg/L) addition. It indicated that NH2OH addition was beneficial to inhibit and wash out NOB. © 2019, Editorial Board of China Environmental Science. All right reserved.
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