What Is Reverse Osmosis?
If a choice had to be made, the Ultra-filtration/Reverse Osmosis process would be elected as state-of-the-art in water treatment technology today. Reverse Osmosis (RO for short) was developed in the late 1950's under U.S. government funding, as an economical method of desalinating sea water - a dream long sought after by mankind.
Reverse Osmosis is revolutionary because it uses a completely new mechanism for processing water - the semi-permeable membrane. Surprisingly enough, it looks a lot like common household sandwich wrap and is composed of very similar polymers (plastics). That's where the similarity ends because this near miracle material is now considered one of the greatest technological achievements of our century.
It's best to look at the semi-permeable RO membrane as providing two distinct water treatment processes. First, it is the ultimate mechanical filter, or ultra-filter, straining out virtually all particulate matter, turbidity, bacteria, microorganisms, asbestos - even single molecules of the heavier organics. To appreciate the fineness of this ultra-filter, as it is referred to in the industry, its pores are on the order of .0005 microns or .0000002 (two ten-millionths) of an inch! That's smaller than can be seen by the best optical microscopes.
Second, it removes dissolved impurities (e.g. mineral salts, toxic metals) - those even smaller than the water molecules themselves - by a remarkable phenomenon known as Reverse Osmosis. With RO, the membrane is said to reject these impurities by repelling them from its surface. It is however permeable to the water molecules so that they diffuse through in a pure state and collect on the opposite side to make the product water.
Overview of Advanced Reverse Osmosis Products:
Variety of Membranes
Membranes are available in a variety of materials. The most common are the so-called cellulosic type. Within this group are cellulose acetate (CA) and cellulose triacetate (CTA).
While CTA is a marked improvement over the original membrane formulation, CA, all cellulosic membranes share one shortcoming. They are susceptible to eventual deterioration from bacterial growth on the membrane surface. While this is rare in regularly disinfected or chlorinated municipal water supplies it can be a real problem when these membranes are used on non-chlorinated or private well supplies. CTA membranes do offer much better resistance to bacterial and chemical attack than CA membranes and have excellent performance on most municipal water supplies.
The latest advances in membrane technology are the new polyamide thin film composite (TFC) types. Based on an entirely new formation, the TFC membranes not only are completely impervious to bacterial attack but they also have superior rejection of impurities, higher water production and increased resistance to adverse water conditions such as pH.