Patent ID: 7820056

Claim:
A coagulation sedimentation process for water to be treated comprising: an inorganic coagulant injection step for injecting an inorganic coagulant into water to be treated, a micro flocculation step for mixing and agitating in a rapid agitation tank the water to be treated into which the inorganic coagulant has been injected to micro-flocculate in advance fine suspended particles in the water to be treated, a flocculation step including a step in which the micro flocks are further flocculated by being brought into contact with existing flocks in a sedimentation basin, and a sedimentation separation step for effecting the sedimentation and separation of the flocks in the sedimentation basin, wherein as a final stage of the flocculation step, a plurality of flock-forming inclined plate whose pitch width is from at least 5 mm to 50 mm or less is provided, and swirling and turbulent currents are created at a lower side end portion of the inclined plates, to accelerate flocculation, and the amount of inorganic coagulant used at a stage of the micro flocculation step is limited so that turbidity of the water to be treated after passage through the inclined plate at a ratio to that before passage is 4/5 or less.