Reverse osmosis (RO) elements and systems force water through semi-permeable membranes to separate water from a solution of dissolved solids. This product area includes RO elements that perform the filtration and separation, as well as complete RO systems that include pumps, piping, and control.
RO Elements and Membranes
Applying pressure to a solution causes water and other molecules with a low molecular weight to pass through a membrane. Larger molecules are retained by this membrane, which is often made of aromatic polyamides or cellulose acetate.
When specifying membrane material, buyers should consider pH and temperature.
- Aromatic polyamide membranes are thin films bonded to layers of porous but supportive materials. Thin-film composite membranes are suitable over a pH range of 2 to 11 and can tolerate temperatures as high as 115 degrees F.
- Cellulose acetate membranes are designed for a pH range of approximately 2.5 to 7 and can handle a maximum temperature of about 85 degrees F.
RO elements that use other types of membranes may also be available.
RO Systems and Components
Large-scale commercial and industrial RO systems incorporate strainers, pressure vessels, centrifugal and pressure-booster pumps, sediment and carbon filters, feed and system pressure gauges, and permeate and concentrate flowmeters. The strainer removes large, suspended solids from the feed solution. The booster pump increases the feed solution’s pressure, typically to an operating range between 150 and 800 psi. Sediment or carbon cartridge filters are used to remove particulates that range between one and five microns.
Optional equipment for RO systems may include a flush system, pH monitor, temperature gauge, feed booster pump, and chemical dosing system. Reverse osmosis systems with an integral microprocessor or controller are also available. Typically, these systems provide features such as motor-actuated feed valves, automatic shut-down during low-pressure (LP) or high-pressure (HP) fault conditions.
Specifications and Applications
RO elements and systems differ in terms of specifications and applications. Product specifications include permeate flow rate, which is usually measured in gallons per day or liters per day; minimum salt rejection stabilized salt rejection, amounts which are expressed as a percentage; and dimensional specifications such as length, width, and diameter. Water temperature and total dissolved solids (TDS) are also important specifications to consider.
In terms of applications, some RO systems are used in finishing applications such as electroplating. Other reverse osmosis systems are used in food and beverage processing, pharmaceutical production, and semiconductor feed-water applications. Complete RO systems with pumps, pipes, and controls are used in municipal systems.