Reverse osmosis is a water purification process that removes 95-99% of most water contaminants including microorganisms, organic compounds, and dissolved inorganic compounds. Contaminant concentrations in municipal water supplies have wide seasonal fluctuations. Therefore, simply filtering and disinfecting municipal water may not provide water of reliable and controlled quality for laboratory animals, particularly in animals developed for highly refined applications such as specific-pathogen-free, immunocompromised, transgenic, and knock out animals. Using reverse osmosis, the animal facility can remove contaminants from animal drinking water. Contaminants removed by reverse osmosis include; microorganisms, microbial by-products such as endotoxins and pyrogens, and many carcinogenic compounds. These contaminants add uncontrolled variables to research involving laboratory animals and can adversely affect animal health.
Osmosis is defined as the movement of a dilute solution through a semi-permeable membrane into a solution of higher concentration that tends to equalize the concentrations of the solutions on both sides of the membrane2. For example, if equal amounts of unfiltered tap water and pharmaceutical water for injection were placed on either side of a semi-permeable membrane, much of the purified water would cross the membrane into the tap water, making the tap water more dilute. Depending upon the permeability of the membrane, some of the contaminants would also cross into the pure water side until both sides had equal concentrations of contaminants that are able to cross the membrane (Figure 1).
| Figure 1. Osmosis. During osmosis, particles pass from areas of high concentration to areas of low concentration as allowed by the pore size of the membrane. Fluid passes from areas of low concentration to areas of high concentration |
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Reverse osmosis uses the concept of osmosis and applies pressure to the side of the membrane containing the concentrated solution, with the result that the fluid is forced through a specialized membrane. Solution contaminants are removed, resulting in a purified, dilute fluid. Using the above example, if equal amounts of unfiltered tap water and pharmaceutical water for injection were placed on either side of a reverse osmosis membrane, during reverse osmosis, water is forced from the tap water side into the purified water side. However, due to the nature of the membrane and the applied pressure, the contaminants do not cross the membrane (Figure 2). Ninety-five to 99 percent of organic compounds, dissolved ions, heavy metals8, and microorganisms (bacteria, fungi, and viruses) can be removed from water with reverse osmosis3.
| Figure 2. Reverse Osmosis. During reverse osmosis, fluid passes from areas of high concentration to areas of low concentration because pressure forces fluid through the membrane. Because the membrane does not contain true pores, most contaminants cannot pass through the membrane7. |
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