What is Reverse Osmosis ?
To understand reverse Osmosis we must first understand osmosis. During natural osmosis, water flows from a less concentrated solution through semipermeable membrane to a more concentrated saline solution until concentrations on both sides of the membrane are equal. (see figure 1)
Reverse osmosis requires external pressure to reverse natural osmotic flow. As pressure is applied to the saline solution, water flows from a more concetrated saline solution through the semipermeable membrane.
Why Reverse Osmosis ?
Reverse Osmosis Membrane
A reverse osmosis membrane has a thin microporous surface that rejects impurities but allows water to pass through. The membrane rejects bacteria, pyrogens, and 85%-95% of inorganic solids. Polyvalent ions are rejected easier than monovalent ions. Organic solids with a molecular weight greater than 300 are rejected by the membrane, but dissolved gases pass through. Reverse osmosis is a percent rejection technology. The purity of the product water depends on the purity of the inlet water. The purity of reverse osmosis product water is much higher than the purity of the feedwater.
Microfiltration is a low-pressure membrane process for separating suspended solids from a feed stream. Water, salts, and select macromolecules pass through a semi-permeable membrane, while suspended solids are retained and progressively concentrated.
Ultrafiltration is a low-pressure mem-brane process for separating high molecular weight species from a feed stream. Water, salts, and low molecular weight species selectively pass through a semi-permeable membrane, while macromolecules and suspended solids are retained and progressively concentrated.
Reverse Osmosis is a high-pressure membrane process for separating low molecular weight species from a feed stream. Water selectively passes through a semi-permeable membrane, while salts and macromolecules are retained and progressively concentrated.