Abstract
The contact aeration processes have many applications in small sewage treatment plants in rural areas. The processes favour the nitrogen removal ability even during the winter season when waste water temperature is low. It has been observed that the nitrification did not occur vigorously when the temperature of waste water was less than 15°C. Hence, to increase 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. In contrast, the anaerobic tanks were previously placed before the aeration tanks. Return flow circulation was introduced within the aeration tanks rather than the treated water after aeration process would return to the first anaerobic tank. The waste water temperature was maintained around 13°C because it was not below from 13°C even in the Tohoku and Hokkaido regions. This type of arrangement lead to almost complete nitrification. However, denitrification did not progress under the condition. Therefore, intermittent aeration in the first aeration tank and circulation flow of 1-Q within the aeration tanks were used. In addition, the anaerobic tanks had circulation flow equivalent to 4-Q. Results reveal passably good agreement of nitrogen removal that T-N concentration of effluent less than 10mg·l-1 was observed. From the results, we would like to propose a system of the Experiment 5 for nitrogen removal of contact aeration process.
