Membrane based desalination apparatus with osmotic energy recovery and membrane based desalination method with osmotic energy recovery

A membrane based desalination method comprising:

• achieving a first solution from salinity water source;
• pressurizing the first solution in a first pressure exchange device;
• separating the first solution into a second solution and a third solution;
• pressurizing the second solution;
• pressurizing the third solution in a second pressure exchange device;
• mixing the second solution and the third solution as a fourth solution;
• providing the fourth solution to a first semi-permeable membrane to achieve product water;
• providing a fifth solution, which is the fourth solution excluding the product water, to the second pressure exchange device for pressurizing the third solution;
• providing the fifth solution to a second semi-permeable membrane after pressurizing the third solution;
• achieving a sixth solution which has lower salinity than the fifth solution;
• and
• providing the sixth solution to the second semi-permeable membrane for drawing water from the sixth solution to the fifth solution by salinity gradient,
• wherein after drawing water from the sixth solution to the fifth solution, the fifth solution is given to the first pressure exchange device for pressurizing the first solution.