DESALINATION APPARATUS AND DESALINATION METHOD, METHOD FOR PRODUCING FRESH WATER, AND METHOD FOR CO-PRODUCING FRESH WATER, SALT AND VALUABLE-MATERIAL

摘要

PROBLEM TO BE SOLVED: To provide a desalination apparatus and desalination method capable of removing multivalent ions contained in the desalinated water from an electrodialysis unit and improving the purity of the recovered valuable-material, and to provide a method for producing fresh water, and a method for co-producing fresh water, salt and valuable-material.SOLUTION: The desalination apparatus comprises: a reverse osmosis membrane unit 12 for obtaining a fresh water Wwhose salt content contained in supplied feed seawater (raw water) W has been removed and a salt-content enriched water Wwhose salt content in the feed seawater W has been enriched; an electrodialysis unit 13 for obtaining an enriched saline water Wand a diluted saline water Wby electrodialyzing the salt-content enriched water W; desalination means (for example a filtration membrane separation unit comprising NF membrane/RO membrane) 15 for enriching multivalent ions and permeating mono-valent ions in the diluted saline water W; and a recirculation line Lfor recirculating the permeated water Wcontaining mono-valent ions that has been permeated by the desalination means 15, to the feed seawater (raw water) W on the inlet side of the reverse osmosis membrane unit 12.