Reverse Osmosis Drinking Water Filter Systems | |
Reverse
Osmosis Explained Ultra-filtration/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. RO's Claim
to Fame
How RO
Works: In Practice Now that the membrane is in a usable form it must be put in some type of container (called a pressure vessel) so pressure can be maintained on its surface. It is this pressure that supplies the energy to force the water through the membrane, separating it from the impurities. The most amazing aspect of RO is that the contaminants left behind are automatically diverted to a waste drain so they don't build up in the system as with conventional filters and purification devices. This is accomplished by using a part of the unprocessed water (feed water) to carry away the rejected impurities to the drain, thus keeping the membrane clean. The flow of impurities to the drain is often referred to as reject water. This is the secret to why RO membranes can last so long and perform like new with minimum maintenance even after years of operation. It is also the reason behind the low cost of producing RO water. Variety
of Membranes 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. They do have one disadvantage at this time and that is being susceptible to chemical deterioration from chlorine and other oxidizers. |