[Effects of Solid Retention Time on the Phosphorus Removal and Nitrosation Granules System]

In this paper, the low C/N ratio of domestic sewage was studied, and mature phosphorus removal granules were inoculated to investigate the effect of solid retention time(SRT)on phosphorus removal and nitrification granular sludge at middle-low temperatures (14-21℃). The test showed that at room temperature (20℃±1℃), the enrichment of AOB in the phosphorus removal granules can be achieved with 30 d SRT and 5 L·(h·L)^-1 aeration intensity, while the NAR was over 90%. When the temperature was lowered to 15℃ and the SRT was 40 d, the phosphorus removal performance deteriorated, and the granule structure became loose with the formation of filamentous bacteria. Relatively sufficient oxygen destabilized nitrosation and the NAR dropped by 22.4%. NOB does not have the ability to quickly adapt to environmental changes. The 12 d anaerobic starvation and sludge removal strategy weakened the relative activity of NOB and quickly restored the performance of phosphorus removal and nitrosation. Batch experiments showed that the temperature dropped from 20℃ to 15℃, and the PAOs still maintained a high oxygen utilization rate, but the SOUR of the AOB decreased by 18%. At this time, the temperature, not the dissolved oxygen concentration, restricted the ammonia oxidation ability. Controlling the sludge age to 30 d, while reducing the aeration intensity to 4 L·(h·L)^-1, achieved stable operation of phosphorus removal and nitrosation at a low temperature (15℃±1℃).