Reverse osmosis and the semi-permeable anisotropic membrane
A turning point for drinking water: Reverse osmosis and the semi-permeable anisotropic membrane
Reverse osmosis (RO) is a seemingly simple but very important water filtration method that has affected millions of lives worldwide. Removing even the smallest particles from water, RO has become the most common method for desalination, the process by which pure water is extracted from salt water. The introduction of this process can be traced back to the work of Canadian chemical engineer Srinivasa Sourirajan and colleague Sidney Loeb.
During the late 1950’s at the University of California Los Angeles (UCLA), Sourirajan and Loeb were both graduate students working on new methods for desalination. After trying numerous materials, came across an effective configuration consisting of a thin anisotropic cellulose acetate film supported by a porous layer. This semipermeable membrane allows water to pass through, but blocks the passage of large molecules or ions. In nature, solvents like water tend to move through these membranes from areas of low to high solute concentration until the two have reached a state of equilibrium. This process, called osmosis, results in a certain pressure exerted on the membrane. By applying a hydrostatic pressure in excess of the osmotic pressure, osmosis can be reversed, and pure water can be extracted while leaving the concentrated solute solution on the original side of the membrane.
After his time at UCLA, Sourirajan came to work for the National Research Council (NRC) in Ottawa, Ontario, where he still resides. He was the founder and first director of the Industrial Membrane Research Institute at the University of Ottawa, working on membranes for other applications such as kidney dialysis. Sourirajan received an Honorary Doctorate from the U of O in 1994.
This breakthrough in desalination led to the first commercial plant to open in Coalinga, California, in the 1960’s. The discovery by Sourirajan and Loeb continues to be used worldwide by countries without access to significant fresh water sources today.