REVERSE OSMOSIS PROCESS THEORY

Reverse osmosis is a mechanical method of reversing the natural process of osmosis in order to remove dissolved minerals, salts, organic molecules and other contaminants from water. Osmosis occurs naturally in living organisms where fluids can selectively pass through cell walls. In the osmosis process, if a dilute water solution is separated from a more concentrated solution (one containing a higher salt concentration) by a semi-permeable membrane, pure water will tend to flow through the membrane and dilute the more concentrated solution. This process will continue until the two solutions reach osmotic equilibrium, or equal ionic concentrations.

In the reverse osmosis process, pure water from the concentrated solution is forced through the semi-permeable membrane into the more dilute solution (the opposite direction of natural osmosis flow). This process will increase the salt concentration of the concentrated solution by removing pure water and leaving behind the dissolved mineral salts. In order to accomplish this flow reversal, an external pressure must be applied to the concentrated solution. In an industrial reverse osmosis system, high pressure pumps are used to generate this required pressure.

SYSTEM OPERATION:

In an actual industrial reverse osmosis application, the concentrated solution is considered to be the source water that is to be purified. The dilute solution is considered to be the purified process water and is called the "permeate". In practice, the source water, or concentrated solution, is continuously replenished by the high pressure pump as it loses pure water through the membrane. If the reverse osmosis process were allowed to continue as described above, the membrane would quickly collect and hold so much of the dissolved salts from the concentrated solution that a salt block would form on the membrane. This of course would stop the process and restrict practical applications to only very small quantities of purified water production. Industrial reverse osmosis systems solve this problem by continuously allowing a small, controlled stream of concentrated water to be drained from the membrane system to maintain the concentrated salt in a solution state. This drain flow is called the "concentrate".

Now it can be seen that an industrial reverse osmosis system separates the source water into two discrete flows: the concentrate and the permeate. In order to maximize efficiency of the system and prevent excess water to be drained from the system through the concentrate flow, great care must be taken in the hydraulic design of an industrial reverse osmosis system. Properly designed reverse osmosis systems will typically be able to recovery up to 75% of the water that enters the system as permeate. This means that for every 75 gallons of purified water, 25 gallons of concentrate are used to remove the dissolved salts from the reverse osmosis membrane.

The quantity and quality of the permeate produced from an industrial reverse osmosis system depends upon the source water’s temperature and salt concentration, the available membrane surface area and type of membrane and the pressure applied by the high pressure pump. It is important to properly select the type of reverse osmosis membrane in order to achieve the best results in a particular purification application. High performance membranes used to produce high purity water can remove up to 99.6% of the dissolved salts from the source water. Reverse Osmosis membranes are also capable of removing organic

In most cases, it is essential to provide filtered or treated water to the industrial reverse osmosis system for best system efficiency. Removal of oxidizing agents, such as chlorine, is commonly required. High levels of certain minerals, such as calcium, magnesium, iron and silica in the source water can cause problematic deposit formations on the membrane surfaces. Bacteria and other organics can also foul the reverse osmosis membrane surfaces and should be eliminated from the feed water. These contaminants can usually be easily removed through traditional water conditioning techniques, thus allowing more efficient, effective and maintenance free reverse osmosis system operation.

REVERSE OSMOSIS APPLICATIONS:

Reverse osmosis technology has been successfully used in a wide variety of water and chemical solution purification processes. Reverse osmosis can be used in nearly any application that requires the removal, or concentration, of inorganic salts, larger organic molecules, colloids, some colors and dyes and fine particulate matter. HydroMax, Inc. builds industrial reverse osmosis systems for applications requiring from 150 to over 100,000 gallons per day of high quality water.