Patent ID: 8795531

Claim:
A co-producing apparatus for salt and fresh water comprising: a raw water supply line that supplies raw water; a pretreatment apparatus that filters a turbid content of the raw water so as to produce pretreated water; an electrodialyzer that electrodialyzes the pretreated water so as to produce concentrated brine and diluted brine; an evaporator that evaporates the concentrated brine so as to produce condensed water and evaporated water; a dryer that produces salt by drying the condensed water; an acid adding unit that adds acid to the diluted brine; a reverse osmosis membrane apparatus having a reverse osmosis membrane that produces (i) fresh water that is permeated water obtained by removing a salt content from the diluted brine to which the acid is added and (ii) salt-enriched membrane separation concentrated water; a recycle line that brings a part of the salt-enriched membrane separation concentrated water back to a rear flow side of the pretreatment apparatus as a recycling membrane separation concentrated water; a water discharge line that discharges a rest part of the salt-enriched membrane separation concentrated water into a sea area as a discharging membrane separation concentrated water; an ion concentration meter that detects ion concentrations of divalent ions and SO 4 2− ions of the recycling membrane separation concentration water, the ion concentration meter being provided on the recycle line; a control apparatus that controls to adjust a ratio between a discharging amount of the discharging membrane separation concentrated water to be discharged into a sea area and a supplying amount of the raw water of the raw water supply line in response to the detected ion concentrations so that these ion concentrations are equal to or less than a saturation concentration of gypsum, wherein produced water is obtained by combining the evaporated water supplied from the evaporator with the permeated water supplied from the reverse osmosis membrane apparatus.