METHOD FOR CONTROLLING INJECTION OF CHEMICALS IN WATER PURIFICATION PLANT

PURPOSE:To hold the alkalinity of raw water after the injection of a flocculant to a prescribed value or more, by controlling the injection of an alkali agent by the alkalinity of raw water and the lowering degree of the alkalinity due to the injection of the flocculant. CONSTITUTION:In a water purification plant consisting of a water introducing well 1, a chemicals mixing basin 2, a flock forming basin 3 and a precipitation basin 4, by using the turbidity TU, the alkalinity AL0, the chlorine requirement CLR and the objective value RCL of the residual chlorine concn. of raw water RW detected by a water quality meter 5 as input values, a flocculant injecting ratio PL, the lowering degree AL1 in alkalinity due to the injection of the flocculant, the alkalinity AL2 after the injection of the flocculant, a chlorine injecting ratio PCL, the lowering degree AL3 of the alkalinity due to the injection of chlorine, the alkalinity AL4 of treated water and the injecting ratio DA of an alkali agent are successively asked by operators 7, 13, 14, 16, 19, 20, 22 and the flow amount F of raw water RW is further put in multipliers 8, 17, 23 to calculate the injection amount of the flocculant, FC, chlorine CL and the alkali agent NL.