Reverse osmosis membranes have been commonly used for everything from household drinking water purification to large-scale desalination of seawater and industrial wastewater treatment for more than 50 years. Although they are common, RO membranes are far from a stagnant technology. As companies and homeowners demand more efficiency and lower costs, not to mention more environmentally friendly technologies, manufacturers have developed increasingly low-energy (LE) and low-pressure (LP) membranes to keep up.
The terms low-energy and low-pressure are often used synonymously when referring to RO membranes. According to experts we spoke to, the lowest membrane option available on the residential market is 50 psi, while the lowest available on the commercial market is 80 psi. The psi indicates the pressure that is necessary to achieve the flow rate associated with that particular membrane.
For large-scale RO in the commercial, municipal and industrial sectors, membranes are being developed that have increasingly low operating pressures, resulting in less water use. In the past 15 years, according to experts, commercial membranes have jumped from a norm of 225 psi to below 100 psi. Other recent advances in membranes includes the switch from a one-leaf to a two-leaf element, resulting in more efficient systems with longer element life, higher rejection, higher contaminant removal and less membrane replacement.
LP and LE membranes present the largest benefit to less developed areas of the world, according to experts, where factors such as line pressure and temperature may be difficult to control. If you start with the lowest energy membrane available, they will be efficient despite other factors. In developed nations, commercial applications can use LP and LE membranes to reduce the pressure of pumps, which in turn puts less pressure on the piping and the entire system, extending its lifecycle.
While LP and LE membranes can change the water quality slightly, the difference is negligible for most applications. High rejection membranes that produce the highest quality water, with up to 99.6 percent rejection of TDS, operate at a high pressure of 225 psi and have few applications, which may include pharmaceutical or microchip manufacturing. The standard LE membrane products have a rejection rate of anywhere from 98.5 to 99 percent, suitable for most standard applications.