Abstract
We have developed a double tank type intermittent aeration process as a system to perform biological simultaneous removal of nitrogen and phosphorus. This process adopts a time-shared system to freely set anaerobic, anoxic or aerobic condition in the aeration tanks, and specializes the functions of the two aeration tanks perform stable removal of nitrogen and phosphorus.
This system was applied to a pilot plant with a treatment volume of 21.3m3·d-1, and continuous experiment has been conducted using actual sewage for one year. From the result of this experiment, we obtained the following removal ratios : 97.9% for BOD, 94.1% for SS, 91.0% for T-N, and 85.0% for T-P. Research on one cycle of the experiment proved that ORP bending point is useful as an index of the end of denitrification and the beginning of phosphorus release. The change in time ratios in each biological reaction and Kr value in each reaction tank revealed that high loading operation in the 1st aeration tank allows maximum removal of pollutant components and accomodation of fluctuating inflow loading to some extent, which enables the 2nd aeration tank to be operated with sufficient time to remove these pollutants.
