Nitrogen and phosphorus removal processes under different aeration strengths in the principal-type tank of alternate...

The alternate multiple tanks (AMT) system was a new highly compact sewage treatment with cost-effective balance and automated management. Dissolved oxygen (DO) and oxidation-reduction potential (ORP) as monitoring indicators are closely linked to contaminants and controlling strategy. Thus, this paper was to investigate the N and P removal mechanisms and the real-time control under different aeration strengths through the principal-type tank. Results showed that N and P removal could reach an optimal balance when the air-water ratio (Rs) was 30 with 540L-air/h and 18L-water/h. Under such a condition, 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. However, restrained aeration reduced the P release and uptake efficiencies and retarded the ammonia oxidation and nitrification, and excessive aeration broke the balance of P release and uptake, prevented denitrification, and had no more effect on nitrification. Inadequate aeration caused residual DO low and insensitive to controlling critical points, while redundant aeration was of no extra effect compared to moderate aeration. An enhanced practical real-time response was obtained, where characteristic points of TP and nitrogen were sensitive to the DO, ORP and systematic manipulation.