Industrial Chemistry and Aqua Technology

Membrane Technology-Nano Filtration and Reverse Osmosis

Osmosis is a natural phenomenon in which a solvent (usually water) passes through a semipermeable barrier from the side with lower solute concentration to the higher solute concentration side. To reverse the flow of water (solvent), a pressure difference greater than the osmotic pressure difference is applied as a result, separation of water from the solution occurs as pure water flows from the high concentration side to the low concentration side. Reverse osmosis membrane separations are, most importantly, governed by the properties of the membrane used in the process. These properties depend on the chemical nature of the membrane material (almost always a polymer) as well as its physical structure. Membranes occupy through a selective separation wall. Certain substances can pass through the membrane, while other substances are caught.

Membrane filtration can be used as an alternative for flocculation, sediment purification techniques, adsorption (sand filters and active carbon filters, ion exchangers), extraction and distillation. The choice of membrane depends upon the nature of the input of water and it is essential to be able to use the most suitable one in any particular set of circumstances.