[Effect of On/Off Aeration Time Ratio Under High Frequency On/Off Aeration on Performance of Nitrosated Granular Sludge].

The inhibition of the on/off aeration time ratio on nitrite oxidizing bacteria (NOBs) in intermittent aeration is the key to accumulating nitrite. This study explores the stable operation of nitrosated granular sludge under the same frequency of aeration and different combinations of stop exposure time. At 25-28, aerobic granular sludge was inoculated into a sequencing batch reactor (SBR) (R0) and acclimatized to nitrosated granular sludge by intermittent aeration and dissolved oxygen (DO) restriction. The effects of different on/off aeration time ratios in one sub-aeration cycle (3 min:3 min; 4 min:2 min; 2 min:4 min) on the performance of nitrosated granular sludge were analyzed using three same sets of SBRs (R1, R2, and R3). Experiments showed that the nitrite accumulation rates of R1 and R2 were higher, with average nitrite accumulation rates of 89% and 95%, respectively. The nitrosation performance of R3 was poor, and the nitrite accumulation rate at the end of the operation cycle was only 57%. The results showed that when the off-aeration time was between 2 and 4 minutes, the longer the off-aeration time was, the more stable the granular sludge structure was; hence, a good nitrosation performance could be maintained. When the off aeration time was less than 2 minutes, the alternation of anaerobic and aerobic environment could not be fully realized, which resulted in the sludge tending to stay in an environment of continuous aeration. Thus, the environmental advantage of intermittent aeration was lost; the NOBs could not be inhibited, and the granular sludge was disintegrated thereby leading to the deterioration of the nitrosation performance. Additionally, the longer aeration time contributed to the development of irregularly shaped particles. The longer the off-aeration time was, the higher the PN/PS value was, which was beneficial to the enhancement of the hydrophobicity of the particle surface and the sludge settling performance.