Abstract
The contact aeration processes are being widely used for the rural sewage treatment systems. Such processes seem to encourage the nitrogen removal ability even during winter season. The observation data of prototype contact aeration process show that the nitrification did not occur vigorously when the temperature of mixed liquor was less than 15°C. In order to enhance the nitrification capability, the flow pattern of the treatment process was renewed in such a way that the aeration tanks were placed before the anaerobic tanks. On the contrary, the anaerobic tanks were previously placed before the aeration tanks. Return flow circulation was introduced within the aeration tank instead of the waste water after aeration process would return to the first anaerobic tank. Further, the volume of aeration tank was increased to about 1.5 times. The mixed liquor temperature was set around 13°C because it was not below 13°C even in the Tohoku and Hokkaido regions. As the result of the experiments under such conditions, nearly 100% nitrification was achieved.
