[Effect of Dissolved Oxygen on Partial Nitrification of Suspended and Attached Growth Systems]

Dissolved oxygen (DO) is an important factor in controlling the partial nitrification process, and it has different effects on different biological treatment systems. The effect of different DO on performances of the partial nitrification process in suspended and attached growth systems, and the changes of microbial community structure by high-throughput sequencing technology were all investigated. The results showed that for a suspended sludge system, the ammonia oxidation rate (AOR) increased from 18.08 mg·(L·h)^-1 to 30.27 mg·(L·h)^-1 when the DO increased from 0.25 mg·L^-1 to 0.50 mg·L^-1. The ammonia nitrogen (NH₄⁺-N) in influent was completely changed into nitrate-nitrogen (NO₃^--N) after a 14-day operation; when the DO was kept at 3.00 mg·L^-1, it needed 77 days to restore the short-cut nitrification effect by reducing DO. In the attached growth system, the AOR was maintained within a narrow range of 11.50-13.50 mg·(L·h)^-1 when DO increased from 2.50 mg·L^-1 to 3.00 mg·L^-1. When DO was at 3.00 mg·L^-1, the ratio of NH₄⁺-N to nitrite nitrogen (NO₂^--N) in the effluent was maintained within 1:1.2 to 1:1.7 through investigating the results from an 80 day operation, and the ratio could meet the influent requirement of the anaerobic ammonium oxidation (ANAMMOX) process. Microbial community structure analysis indicated that the abundance of the Nitrosomonas genus belonging to ammonia-oxidizing bacteria (AOB) increased from 10.07% to 18.64% when the DO increased from 0.25 mg·L^-1 to 3.00 mg·L^-1 in a suspended sludge system; the abundance of the Nitrosomonas genus in the biofilm system was 20.43% and that of the Candidatus_Kuenenia genus was 0.78% when DO was 3.00 mg·L^-1. Conclusively, the biofilm system could be used as a pretreatment unit for the ANAMMOX process, because the partial nitrification process was less affected by DO and the partial nitrification rate was more stable.