PURPOSE: To keep const. quality of treated water inexpensively, by discharging const. quantity of deactivated carbon and charging const. quantity of fresh activated carbon periodically, by detecting DCD and inorg. reducing mateial concn. of raw water or treated water, and by conducting discharge and charge of the activated carbon in order to keep the treated water at a target COD level or lower.

CONSTITUTION: A fixed quantity of deactivated carbon is discharged at a prescribed period from a discharging mechanism 5 of an adsorption column 1 to a reservoir 6, simultaneously the equal amount of fresh or regenerated activated carbon is replenished from a reservoir 4 to the top of the column 1. A detected value D given by a sensor 10, which is attached to a raw-water supply tube 2, of an org. material concn. monitor 8 of water quality detector 7 and a detected value D' given by a sensor 10 of an inorg. reducing material concn. monitor 9 are fed to a control signal output unit 12, which computes on the basis of the detected values the org. material concn. Ce of the treated water from the adsorbability of the adsorption column 1 at the time of concn. detection. When the Ce exceeds the target org. material concn. Ci, the output unit 12 gives a discharge signal to the activated carbon discharge unit 5 so as to discharge a fixed quantity of deactivated carbon, at the same time equal quantity of fresh activated carbon is replenished from the reservoir 4. Water quality is detected at a const. interval of time, if necessary, at a discharge pipe 3.