Composite semipermeable membrane, spiral membrane element, water treatment system, and water treatment method

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.