Method of Flocculating Sedimentation Treatment

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 flock-forming inclined plate whose pitch width is from at least 5 mm to 50 mm or less is provided and the inorganic coagulant at a stage after the micro flocculation step is limited for a used amount 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.