WATER TREATMENT SYSTEM, WATER TREATMENT METHOD

A water treatment system includes a pretreatment device which generates primary treated water by performing pretreatment on water to be treated; a membrane separation device having a reverse osmosis membrane through which the primary treated water passes to be separated into concentrated water and permeable water; a first sensor device provided between the pretreatment device and the membrane separation device to detect the presence or absence of the occurrence of biofouling caused by the primary treated water; a second sensor device provided on a downstream side of the membrane separation device to detect the presence or absence of scale precipitation caused by the concentrated water; and a control device which determines operating parameters including a supply pressure and a supply flow rate of the primary treated water to the membrane separation device, on the basis of a biofouling amount and a scale precipitation amount.