Reverse Osmosis (RO)

Overcoming osmotic pressure

In ordinary osmosis, when a semipermeable membrane separates solutions of differing solute concentrations, the lower-concentration solution flows into the higher-concentration solution in attempt to reach equilibrium: an equal degree of solute concentration on both sides of the membrane. As the amount of solution on the higher-concentration side increases, pressure on that water column rises until it is high enough to hinder the flow of the lower-concentration solution across the membrane. This is the action of osmotic pressure.

In reverse osmosis (RO), pressure that exceeds a system’s osmotic pressure is applied to that system. The pressure forces the higher-concentration solution back across the semipermeable membrane, leaving solutes that are blocked by the semipermeable membrane behind.

Typically, reverse osmosis water treatment results in a rejection of dissolved salts that is 95 – 99 percent or greater, depending on membrane type, feed composition, temperature, and system design.

Reverse osmosis water treatment can provide finer filtration than either nanofiltration or ultrafiltration. Using RO as a pretreatment process for ion exchange (IX)  can substantially reduce the operating costs and regeneration frequency of the IX system.

Typical applications include:

• Purification of home drinking water.

• Desalination of seawater or brackish water to produce drinking water.

• Wastewater recovery.

• Food and beverage processing.*

• Biomedical separation.

• Industrial process water treatment.

Reverse osmosis water treatment is also often used to produce ultrapure water for the semiconductor industry , in boiler water treatment for the power industry, and for applications in the health care and bioprocessing industry.