Patent ID: 10294127

Abstract:
To enable energy-saving operation and stable supply of permeate water while water quality level of the permeate water is satisfied during operation, clarified seawater sw subjected to pretreatment and stored in to-be-treated water tank 12 is supplied to reverse osmosis membrane module 14 via clarified seawater supply passage 16. Permeate water pw obtained by an earlier stage element of the reverse osmosis membrane elements 36 of the reverse osmosis membrane module 14 is sent to a subsequent process from permeate water sending passage 46, and permeate water pw obtained by the reverse osmosis membrane element 36 is circulated into the to-be-treated water tank 12 via permeate water circulation passage 48. The flow rate of the clarified seawater sw supplied to the reverse osmosis membrane module 14 is controlled by variable flow rate high-pressure pump 22 provided in the clarified seawater supply passage 16, and opening degree of flow regulating valve 68 provided in the permeate water circulation passage 48 is controlled, whereby the circulation flow rate of the permeate water is controlled.