CONTROLLING METHOD FOR BIOLOGICAL DENITRIFICATION

PURPOSE:To contrive the curtailment of a power cost by the reduction of DO in a diffuser tank and the optimization of an agitating speed, by adding correction to the speed of agitation in the diffuser tank calculated from a DO value in a nitrifier tank and an inflow amount in the diffuser tank using a DO value in said diffuser tank as a feed back amount. CONSTITUTION:Inflow filthy water 1 is nitrified in a nitrifier tank 2 under an aerobic condition, agitatively deaerated in a diffuser tank 3 to reduce D0, denitrified in a denitrifier tank 4, separated from returned sludge 6 in a precipitation basin 5 and then drained. In this tertiary treatment, the agitating speed of an agitator 7 for the diffuser tank 3 is calculated by a computer 9 on the basis of DO1 measured by the DO meter 13 of the nitrifier tank 2 and an inflow amount F measured by the inflow meter 14 of the diffuser tank 3, to dispatch a speed command as feed forward instruction. On the other hand, a correction value is calculated by another computer 11 on the basis of the difference DELTADO2 between DO2 measured by the DO meter 8 of the diffuser tank 3 as a feed back signal and a set point D0 provided from a DO2 setting unit 10, to correct said speed instruction. Hence, the agitating speed is controlled at the optimum value.