| 摘要 |
PURPOSE:To obtain clear purified water at the time of the low turbidity of raw water, in a water purification plant, by returning the amount of sedimented flocs returned corresponding to the turbidity of raw water to the area between the detection terminal of the turbidity of raw water and the injection point of a flocculant with due regard to the number of sedimented floc particles. CONSTITUTION:The turbidity of raw water is inputted to a comparing circuit 21 and a flocculant 2 is injected in raw water corresponding to the turbidity thereof. The turbidity of raw water is compared with a low concn. set value and, when the turbidity of raw water is lower than said concn. set value, the comparing circuit 21 outputs a turbidity difference value and a return ratio operation circuit 24 calculates a flock return ratio corresponding thereto. A return ratio collection circuit 24 operates the floc return ratio from the state of floc by the signal from a flock sensor 20 and a return amount operation circuit 23 inputs the floc return ratio and the flow amount of raw water from a flowmeter 19 to calculate a floc return amount. Accordingly, a return pump 16 returns the floc sedimented in a sedimentation basin 4 to a chemicals mixing basin 1.
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