Nitrogen and phosphorus removal processes under different aeration strength in principal-type tank of Alternate Multiple Tanks system and process control.

The Alternate multiple tanks (AMT) system was originated by Southeast University to meet pressing requirements of new highly-compact sewage treatment with cost-effective balance and automated management. DO and ORP as economic monitoring indicators are closely linked to nutrients variations and controlling strategy. Thus this paper was to investigate the N and P periodic variations and removal mechanisms under different aeration strengths in scope of principal-type tank in AMT, and the relationship between nutrients and DO, ORP. Results showed that N and P removal could reach an optimal balance when the air-water ratio (Rs) was 30 where the aeration strength was 540L/h under inflow of 18L/h. And under the optimized conditions, the TP, TN, ammonia and nitrate remained 0.4 mg/L (88.4% of removal efficiency), 5.0 mg/L (84.7%), 0.5 mg/L (98.4%) and 4.0 mg/L, respectively during the discharge stage. Restrained aeration reduced the efficiency of P release and uptake and retarded the oxidizing rate of ammonia and nitrification. While excessive aeration broke the balance of P release and uptake, prevented denitrification due to its high residual DO, and had no effect on nitrifying in comparison to moderate aeration. Inadequate aeration caused DO values in low level and insensitive to controlling critical points, while redundant aeration was of no extra use compared to moderate aeration. Based on the processes, an enhanced practical real-time response of DO and ORP to nutrients change and control policy was obtained, where characteristic points of TP and nitrogen were sensitive to the systematic manipulation and DO, ORP variations.