WATER TREATMENT SYSTEM, WATER TREATMENT METHOD

A water treatment system (100) is provided with: a pretreatment device (1) which generates primary treated water by performing a pretreatment on water to be treated; a membrane separation device (2) having a reverse osmosis membrane through which the primary treated water is passed to be separated into concentrated water and permeated water; a first sensor device (3) which is provided between the pretreatment device (1) and the membrane separation device (2) and which detects the presence or absence of occurrence of biofouling caused by the primary treated water; a second sensor device (4) which is provided on a downstream side from the membrane separation device and which detects the presence or absence of scale deposition caused by the concentrated water; and a control device (5) which determines, on the basis of the amount of biofouling and the amount of scale deposition, operation parameters including the pressure and flow rate of the primary treated water being supplied to the membrane separation device (2).