Patent ID: 8012759

Claim:
A method of determining an amount of coagulant to be injected to an amount of water to be treated (coagulant injection rate) in a process of water treatment, which comprises the following steps: (1) collecting a predetermined same amount of the water to be treated in every one of plural sample tanks, and then injecting a predetermined different amount of a coagulant to each water sample collected in those sample tanks, thereby preparing water samples each having a different coagulant injection rate; (2) individually mixing, after the coagulant injection thereto, every water sample to thereby disperse the coagulant therein, and individually determining the time taken before the start of agglomeration of particles in each water sample (agglomeration start time) for every water sample; (3) computing, based on the agglomeration start time determined for every water sample and on the coagulant injection rate for them, the correlation between the agglomeration start time and the coagulant injection rate, as a fitting line; and (4) computing, based on agglomeration start time data previously set for a water treatment plant and on the above fitting line, a coagulant injection rate for the water treatment plant.