Abstract: An embodiment of the present invention includes: a recycle line that brings a part of salt-enriched membrane separation concentrated water 26 back to the rear flow side of a pretreatment apparatus 12; a water discharge line that discharges the remained concentrated water into a sea area; and a control apparatus 31 that controls to adjust the ratio between the discharging amount of the discharging membrane separation concentrated water to be discharged into a sea area and the supplying amount of supplying seawater. A pH is set to be equal to or less than 7.3 by adding acid 21. The salt 18 is obtained from the dryer 19, and produced water (fresh water) 29 is obtained by combining evaporated water 28 supplied from the evaporator 16 with the permeated water 24 supplied from the reverse osmosis membrane apparatus 25.

Abstract: Included is a high-pressure pump P1 that increases the pressure of raw water 11 to a predetermined high pressure, a high-pressure reverse osmosis device 13 including a high-pressure reverse osmosis membrane 13a for concentrating a salt content in high-pressure feed water 12 whose pressure is increased, a first drain valve 21 that is mounted on a permeated water line L2 for supplying the permeated water 14 downstream and temporarily drains permeated water 14 of an initial start-up from a discharge line L6, a low-pressure pump P2 that is mounted on a permeated water line L3 provided downstream of the first drain valve 21 and reduces the pressure of the permeated water 14 to a predetermined low pressure, a low-pressure reverse osmosis device 16 including a low-pressure reverse osmosis membrane 16a for concentrating a salt content in low-pressure feed water 15 whose pressure is reduced by the low-pressure pump P2, and a second drain valve 22 that is mounted on a discharge line L5 at the concentrated water side of

Abstract: The present invention provides a demineralizer capable of leveling out product water quantity and product water quality through the year regardless of raw water temperature, cutting down running costs, and improving the rate of operation. The demineralizer includes: a second reverse osmosis membrane module for separating primary concentrated water into secondary product water and secondary concentrated water; a product water supply pipe for guiding primary product water to a product water tank located downstream thereof; a secondary product water supply pipe for guiding the secondary product water downstream; a return pipe whose one end is connected to one end of the secondary product water supply pipe, and whose other end is connected to a raw water supply pipe; a by-pass pipe whose one end is connected to said one end of the secondary product water supply pipe, and whose other end is connected to the product water supply pipe; and a valve connected at some point in the return pipe and/or the by-pass pipe.