Osmotic desalination methods and associated systems

A method, comprising:

• transporting an aqueous feed stream across a first side of an osmotic membrane;
• transporting a draw inlet stream across a second side of the osmotic membrane such that water is transported from the aqueous feed stream through the osmotic membrane to the draw inlet stream to produce a draw product stream having a lower osmotic pressure than the draw inlet stream and a concentrated aqueous stream having a higher osmotic pressure than the aqueous feed stream;
• wherein the osmotic membrane is operated such that:
• m
• D
• ,
• i
• m
• F
• ,
• i
• =
• C
• 1
• ⁢
• π
• F
• ,
• i
• -
• (
• P
• F
• -
• P
• D
• )
• π
• D
• ,
• i
• +
• (
• P
• F
• -
• P
• D
• )
• wherein PF is a hydraulic pressure at an inlet of the aqueous feed stream to the osmotic membrane;
• mF,i is a mass flow rate of the aqueous feed stream at the inlet of the aqueous feed stream to the osmotic membrane;
• πF,i is an osmotic pressure of the aqueous feed stream at the inlet of the aqueous feed stream to the osmotic membrane;
• PD is a hydraulic pressure at an inlet of the draw inlet stream to the osmotic membrane;
• mD,i is a mass flow rate of the draw inlet stream at the inlet of the draw inlet stream to the osmotic membrane;
• πD,i is an osmotic pressure of the draw inlet stream at the inlet of the draw inlet stream to the osmotic membrane;
• and C1 is from about 0.8 to about 1.2.

A method, comprising:

• transporting an aqueous feed stream across a first side of an osmotic membrane;
• transporting a draw inlet stream across a second side of the osmotic membrane such that water is transported from the aqueous feed stream through the osmotic membrane to the draw inlet stream to produce a draw product stream having a lower osmotic pressure than the draw inlet stream and a concentrated aqueous stream having a higher osmotic pressure than the aqueous feed stream;
• and
• directing the transport of the aqueous feed stream across the osmotic membrane and/or the draw inlet stream across the osmotic membrane such that the following two ratios are within about 20% of each other:
• a ratio of a mass flow rate of the draw inlet stream entering the osmotic membrane to a mass flow rate of the aqueous feed stream entering the osmotic membrane, and
• a ratio of the difference between the osmotic pressure of the aqueous feed stream entering the osmotic membrane and the inlet pressure difference across the osmotic membrane to the sum of the osmotic pressure of the draw inlet stream entering the osmotic membrane and the inlet pressure difference across the osmotic membrane.

A method, comprising:

• transporting an aqueous feed stream across a first side of an osmotic membrane;
• transporting a draw inlet stream across a second side of the osmotic membrane such that water is transported from the aqueous feed stream through the osmotic membrane to the draw inlet stream to produce a draw product stream having a lower osmotic pressure than the draw inlet stream and a concentrated aqueous stream having a higher osmotic pressure than the aqueous feed stream;
• directing the transport of the aqueous feed stream across the osmotic membrane and/or the draw inlet stream across the osmotic membrane such that the transmembrane net driving force at the entrance of the aqueous feed stream to the osmotic membrane and the transmembrane net driving force at the entrance of the draw inlet stream to the osmotic membrane are at least about 10% different from each other;
• measuring at least one of a temperature, a pressure, a solubilized species concentration, and a flow rate of the aqueous feed stream and/or the draw inlet stream;
• and
• changing at least one of the flow rate of the aqueous feed stream and the flow rate of the draw inlet stream such that the transmembrane net driving force at the entrance of the aqueous feed stream to the osmotic membrane and the transmembrane net driving force at the entrance of the draw inlet stream to the osmotic membrane are within about 10% of each other.