Co-producing apparatus for salt and fresh water and co-producing method of the same

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 nanofiltration membrane separation apparatus that removes divalent ions from the diluted brine to which the acid is added so as to produce treated water and membrane separation concentrated water;
• 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 of the treated water supplied from the nanofiltration membrane separation apparatus and (ii) salt-enriched membrane separation concentrated water;
• a recycle line that brings a total amount of the salt-enriched membrane separation concentrated water supplied from the reverse osmosis membrane apparatus back to a rear flow side of the pretreatment apparatus as recycling membrane separation concentrated water;
• a water discharge line that discharges a total amount of the membrane separation concentrated water supplied from the nanofiltration membrane separation apparatus into a sea area;
• an ion concentration meter that detects ion concentrations of divalent ions and SO42− ions of the recycling membrane separation concentrated water;
• a control apparatus that controls to adjust a ratio between a discharging amount of the 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.

A co-producing method for salt and fresh water comprising:

• supplying raw water;
• filtering a turbid content of the raw water, so as to obtain pretreated water;
• electrodialyzing the pretreated water so as to obtain diluted brine and concentrated brie;
• evaporating the concentrated brine to produce salt;
• adding acid to the diluted brine;
• removing a salt content from acid-added diluted brine to obtain (i) fresh water that is permeated water and (ii) salt-enriched membrane separation concentrated water;
• bringing a part of the salt-enriched membrane separation concentrated water as recycling membrane separation concentrated water to the pretreated water;
• discharging a rest part of the salt-enriched membrane separation concentrated water into a sea area as a discharging membrane separation concentrated water;
• detecting ion concentration of divalent ions and SO42− ions of the recycling membrane separation concentrated water;
• and
• adjusting 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 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 with the permeated water.

A co-producing method for salt and fresh water comprising:

• supplying raw water;
• filtering a turbid content of the raw water so as to obtain pretreated water;
• electrodialyzing the pretreated water so as to obtain concentrated brine and diluted brine;
• evaporating the concentrated brine so as to obtain condensed water and evaporated water;
• drying the condensed water so as to obtain salt;
• adding acid to the diluted brine;
• removing divalent ions from the diluted brine to which the acid is added so as to obtain treated water and membrane separation concentrated water;
• producing (i) fresh water that is permeated water obtained by removing a salt content of the treated water and (ii) salt-enriched membrane separation concentrated water;
• brings a total amount of the salt-enriched membrane separation concentrated water to the pretreated water as recycling membrane separation concentrated water;
• discharging a total amount of the membrane separation concentrated water into a sea area;
• detecting ion concentrations of divalent ions and SO42− ions of the recycling membrane separation concentrated water;
• adjusting a ratio between a discharging amount of the membrane separation concentrated water to be discharged into a sea area and a supplying amount of the raw water 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.