Method and apparatus for determination of coagulant injection rate in water treatment process

A method of determining an amount of coagulant to be injected to an amount of water to be treated in a process of water treatment (coagulant injection rate), which comprises the following steps:

• (1) collecting a predetermined amount of water to be treated in one sample tank, then injecting a predetermined amount of a coagulant to the water sample collected in the sample tank, and after the coagulant injection, dispersing the coagulant by mixing, and determining the time taken before the start of agglomeration of the particles in the water sample;
• (2) following step (1), cleaning the sample tank, then again collecting the predetermined amount of the water to be treated in the sample tank, and injecting a different predetermined amount, which differs from that in the above step (1), of the coagulant into the water sample, and determining the agglomeration start time for the water sample;
• (3) repeating the operation of the above step (2) plural times with varying the coagulant injection amount every time, and determining the agglomeration start time for every water sample each having a different coagulant injection amount;
• (4) 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
• (5) 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.