CONTROLLING METHOD FOR BIOLOGICAL DENITRIFICATION PROCESS

PURPOSE:To curtail the consumption amount of methanol and the power cost of an agitator, by controlling the agitating speed of said agitator as a means for the diffusion of DO at the optimum value on the basis of DO values in nitrification and diffusion tanks, and lowering the DO value in said diffusion tank. CONSTITUTION:Since a time lag in the measurement of DO2 in a diffusion tank 3 is formed because of a residence time in said tank 3, a value DO1 measured by a DO meter 7 in a nitrification tank 2 and an objective value DO0 in the tank 3 after being preset are inputted to a comparing circuit 9. DELTADO1 obtd. thereby is inputted to a calculating circuit 15, wherein the agitating speed N of an agitator 10 is obtained in response to DELTADO1 on the basis of the diagram of correlative relationship. The speed N is inputted to a speed regulating means 14, and the reduction of DO in the tank 3 is performed by the feed forward control to control the speed of the agitator 10. If the amount of DO does not become to the value DO0 because of some disturbance, the values DO0 and DO2 are inputted to a comparing circuit 12 by a DO meter 11 in the tank 3, a value DELTADO2 obtd. thereby is inputted to the circuit 15, and correction is added to the command for controlling said speed by feed back control. Hence, the efficiency of controlling is enhanced, and the reduction of DO in the tank 3 is contrived.