Reverse Osmosis Principle
Reverse osmosis, also known as hyper filtration, is the finest filtration known. This process will allow the removal of particles as small as dissolved individual ions from a solution. Reverse osmosis is used to purify water and remove ions and dissolved organic molecules. It can be used to purify fluids such as ethanol and glycol, which will pass through the reverse osmosis membrane, while rejecting other ions and contaminants from passing. The most common use for reverse osmosis is in purifying water. It is used to produce water that meets the most demanding specifications that are currently in place.
If two aqueous solutions of different salinity are separated by a semi-permeable membrane, osmosis will cause water to pass through the membrane in the direction of the more concentrated solution, therefore diluting it. By applying sufficient pressure to the more concentrated liquid, the direction of osmosis can be reversed. In this way, we can mechanically reverse the flow and separate the concentrated solution into its constituents: the water and the dissolved solids. One part is called the permeate, or filtrate, and the other is the reject stream, or concentrate.
Reverse osmosis uses a membrane that is semi-permeable, allowing the fluid that is being purified to pass through it, while rejecting the contaminants that remain. Most reverse osmosis technology uses a process known as crossflow to allow the membrane to continually clean itself. As some of the fluid passes through the membrane the rest continues downstream, sweeping the rejected species away from the membrane, in a concentrated brine reject water.
The process of reverse osmosis requires a driving force to push the fluid through the membrane, and the most common force is pressure from a pump. The higher the pressure, the larger the driving force. As the concentration of the fluid being rejected increases, the driving force required to continue concentrating the fluid increases.
Reverse osmosis is capable of rejecting bacteria, salts, sugars, proteins, particles, dyes, and other constituents that have a molecular weight of greater than 150-250 daltons. The separation of ions with reverse osmosis is aided by charged particles. This means that dissolved ions that carry a charge, such as salts, are more likely to be rejected by the membrane than those that are not charged, such as organics. The larger the charge and the larger the particle, the more likely it will be rejected.
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