Chemical injection control method and chemical injection controller

A chemical injection controller which controls a rate of chemical injection into raw water based on water qualities of the raw water and treated water in a water purification system, the controller comprising:

• optimum chemical injection rate calculation means for calculating an optimum chemical injection rate by correcting a preset chemical injection rate based on a deviation of a measured value of a water quality index of the treated water from a target value of the water quality index, the measured value of the water quality index being obtained by operating a chemical injection pump based on the preset chemical injection rate;
• multiple regression analysis calculation means for performing multiple regression analysis using the optimum chemical injection rate as a target variable and using one or more water quality indices of the raw water as explanatory variables, determining partial regression coefficients of the respective explanatory variables, and thereby deriving a calculation formula for a basic chemical injection rate corresponding to the water quality indices of the raw water;
• basic chemical injection rate calculation means for calculating the basic chemical injection rate corresponding to the water quality indices of the raw water by substituting the measured values of the water quality indices of the raw water into the calculation formula;
• and
• chemical injection rate calculation means for correcting the basic chemical injection rate based on a measured value of the water quality index of the treated water obtained through operation of the chemical injection pump based on the basic chemical injection rate, thereby newly calculating a chemical injection rate, and outputting the newly calculated chemical injection rate as a control factor for the chemical injection pump while supplying the newly calculated chemical injection rate to the optimum chemical injection rate calculation means.