Effect of Different Ratios of Anaerobic Time and Aeration Time on the Formation of Partial Nitrification Granules

Abstract

Flocculent sludge with good nitritation performance and MLSS and SVI values of 3500 mg ·L-1 and 162 mL ·g-1, respectively, was inoculated in the R1, R2, and R3 groups of the same SBR reactors at room temperature (22-28℃). The effects of different anaerobic time and aeration time ratios (1:2, 1:1, and 2:1) on the formation of partial nitrification granular sludge were studied. The results showed that granules in three reactors were successfully formed at 103 d, 82 d, and 64 d. The nitrosation rate of R1, R2, and R3 were 86%, 98%, and 96%, respectively, and SVI decreased to 89, 75, and 58 mL ·g-1 and MLSS increased to 2314, 2781, and 2946 mg ·L-1, respectively, at the 85 d. The larger ratio of anaerobic time and aeration time was more conducive to sludge granulation, better settling, and nitritation performance. When the anaerobic time and aeration time ratio was 1:2, the nitritation performance of the sludge decreased since the NOB could not be suppressed, and the settling performance of the sludge became better and then worse. In addition, at the larger ratio of anaerobic time and aeration time, there was more PN and PS from microbial secretion. The PN of R1, R2, and R3 was smaller at the end of the anaerobic phase compared to that of the aerobic phase in the early stage of granular formation, but were reversed in the stabilization stage. The PS of the anaerobic phase was larger than that of the aerobic stage over the entire process.