Method for concentrating aqueous containing solute into high concentration by hydraulic-membrane process under no difference in osmotic pressure

A method of concentrating an aqueous solution containing a solute to be concentrated, the method comprising the steps of:

• (a) firstly concentrating, by reverse osmosis, the aqueous solution containing a solute to be concentrated, thereby producing a firstly concentrated solute-containing aqueous solution;
• (b) introducing the firstly concentrated solute-containing aqueous solution of step (a) into a zero osmotic pressure difference concentrator comprising a feed chamber and a draw chamber, which are separated from each other by a reverse osmosis membrane, thereby secondly concentrating the introduced solute-containing aqueous solution in the concentrator to produce a secondly concentrated solute-containing aqueous solution;
• and
• (c) recovering the secondly concentrated solute-containing aqueous solution, while recycling a portion of the secondly concentrated solute-containing aqueous solution to the draw chamber to form a zero osmotic pressure difference between the feed chamber and the draw chamber,
• wherein step (b) comprises the steps of:
• (i) transferring the firstly concentrated aqueous solution of step (a) to the feed chamber of the zero osmotic pressure difference concentrator, and introducing into the draw chamber the aqueous solution transferred to the feed chamber having an osmotic pressure identical to that of the aqueous solution transferred to the feed chamber, thereby forming the zero osmotic pressure difference between the feed chamber and the draw chamber;
• and
• (ii) applying a pressure for the reverse osmosis membrane to the feed chamber under the zero osmotic pressure difference condition to transfer water of the concentrated aqueous solution to the draw chamber, thereby further concentrating the concentrated aqueous solution;
• and
• wherein step (c) comprises the steps of:
• (i) transferring 10 wt %-90 wt % of the secondly concentrated solute-containing aqueous solution to the draw chamber to maintain the osmotic pressure of the draw chamber equal to that of the feed chamber;
• (ii) transferring solute-containing aqueous solution from the draw chamber to a reverse osmosis separator to produce a thirdly concentrated solute-containing aqueous solution, and discharging water of the solute-containing aqueous solution to outside;
• and
• (iii) transferring the thirdly concentrated solute-containing aqueous solution to the zero osmotic pressure difference concentrator.