Composite semipermeable membrane, spiral membrane element, water treatment system, and water treatment method
A composite semipermeable membrane 12 of the present invention includes a porous support membrane 12 a and a skin layer 12 b supported by the porous support membrane 12 a . The membrane surface of the composite semipermeable membrane 12 has an elastic modulus of 250 MPa or more and 500 MPa or less as calculated by force curve measurement using AFM in water. A spiral membrane element 20 of the present invention includes the composite semipermeable membrane 12 of the present invention. A water treatment system 100 of the present invention includes the spiral membrane element 20 of the present invention.
1 . A zero liquid discharge water treatment system comprising a spiral membrane element, wherein
the spiral membrane element comprises a composite semipermeable membrane,
the composite semipermeable membrane comprises
a porous support membrane,
a skin layer supported by the porous support membrane, and
a coating that covers the skin layer,
the skin layer comprises polyamide,
the coating comprises a polymer that comprises at least one selected from the group consisting of betaine polymer and polyoxazoline,
a membrane surface of the composite semipermeable membrane has an elastic modulus of 250 MPa or more and 500 MPa or less as calculated by force curve measurement using AFM in water, and
the elastic modulus is a value calculated from a force curve measured by the AFM in water at the position where ultrapure water is dropped on a surface of the coating of the composite semipermeable membrane.
2 . The zero liquid discharge water treatment system according to claim 1 , wherein
the spiral membrane element further comprises a permeate-side flow path material that comprises a tricot knitted material having a knitting density of 31 to 60 wales and 34 to 52 courses, and
the composite semipermeable membrane is in contact with the permeate-side flow path material.
3 . The zero liquid discharge water treatment system according to claim 1 , further comprising:
a low-pressure RO membrane module;
a medium-pressure RO membrane module for further concentrating wastewater that has been concentrated in the low-pressure RO membrane module; and
a high-pressure RO membrane module for further concentrating the wastewater that has been concentrated in the medium-pressure RO membrane module, wherein
the medium-pressure RO membrane module comprises the spiral membrane element.
4 . A water treatment method in a zero liquid discharge water treatment system according claim 1 that further comprises a low-pressure RO membrane module, a medium-pressure RO membrane module comprising the spiral membrane element, and a high-pressure RO membrane module, the method comprising:
concentrating wastewater in the low-pressure RO membrane module;
further concentrating, in the medium-pressure RO membrane module, the wastewater that has been concentrated in the low-pressure RO membrane module; and
further concentrating, in the high-pressure RO membrane module, the wastewater that has been concentrated in the medium-pressure RO membrane module, wherein
a feed pressure to the low-pressure RO membrane module is lower than a feed pressure to the medium-pressure RO membrane module,
the feed pressure to the medium-pressure RO membrane module is lower than a feed pressure to the high-pressure RO membrane module, and
the feed pressure to the medium-pressure RO membrane module is 2.0 MPa or more and 4.0 MPa or less.
5 . The zero liquid discharge water treatment system according to claim 1 , wherein the elastic modulus is 260 MPa or more and 480 MPa or less.