Study on the Denitrification in the Oxidation Ditch Applying Falling Water as an Aerator

Abstract

It is well known that many oxidation ditches have shown a high degree of denitrification. To remove nitrogen, many operation systems of the oxidation ditch have been proposed and used at sewage treatment plants. However, few plants have used falling water as an aerator. In an oxidation ditch, falling water is effectively used as an aerator. The oxidation ditch method applying falling water is as efficient as any other method.
In this paper, intermittent aeration in an oxidation ditch using falling water was investigated for the purpose of removing nitrogen. In this ditch, a pump was used for lifting the water. The intermittent aeration was carried out by on-off operation of the pump.
The experiments of removing nitrogen using this ditch was carried out during November, 1989 and March, 1990. As a result, it was found that a high rate removal of nitrogen was obtained constantly during a mixed liquid temperature below 15°C. When the temperature was above 15°C, higher than 95% of BOD removal ratio and 90% of nitrogen removal ratio were achieved at the same time. The optimum operation for removing nitrogen was carried out under intermittent aeration by 30 min of aeration and 60 min nonaeration as one cycle. In this case, denitrification was achieved during 30-60 min of nonaeration period and nitrification-denitrification processes of activated sludge were effectively accomplished. In the oxidation ditch method, the aerator applying falling water was also effective in removing nitrogen.