Reverse osmosis
reverse osmosis (abbreviation: RO, English Reverse Osmosis ), also known as hyperfiltration (abbreviation: IF ), is the process in which they force the passage of molecules of solvent from the more concentrated solution to less concentrated solution obtained by applying to the solution more concentrated a pressure greater than the osmotic pressure. In practice, reverse osmosis is carried out with a membrane that holds the solute on one side, preventing its passage and allowing the pure solvent to be obtained on the other. This phenomenon is not spontaneous and requires the completion of a job mechanical equal to that necessary to cancel the effect of osmotic pressure. This process represents the finest water filtration technique as it does not simply consist of a physical obstacle, determined by the size of the pores, to the passage of the molecules, but exploits the different chemical affinity of the species with the membrane, in fact allowing the passage of the hydrophilic (or water-like ) molecules, i.e. chemically similar to water, for example, short-chain alcohols. From a plant engineering point of view, the method exploits the principle of tangential filtration, as well as other separation techniques using membranes such as microfiltration, ultrafiltration, and nanofiltration. Reverse osmosis is used in the treatment of water both for desalination and for the removal of traces of phosphates, calcium and heavy metals, pesticides, radioactive materials, and almost all polluting molecules It is also used in industry as an industrial Ro plant. In recent years, "zero liquid discharge" plants have been built in which the reverse osmosis section increases the concentration of the chemical species present in the wastewater up to values close to or higher than their solubility (supersaturated solutions). In the reverse osmosis process, thin-film composite membranes (TFC or TFM, Thin Film Composite Membrane ) are used. These membranes are semipermeable and mainly manufactured for use in water purification or in desalination systems. They also have used in chemical applications such as batteries and fuel cells. Basically a TFC material is a molecular sieve built in the form of a film of two or more layered materials. The membranes used in osmosis are generally made of polyamide, a substance is chosen mainly for its permeability to water and its impermeability to the various dissolved impurities, including saline ions and other small molecules that cannot be filtered. Another example of a semipermeable membrane is the one used in dialysis
Hand operated desalination filters
Small manually operated reverse osmosis filters were initially designed for the military in the late 1970s for personal survival equipment or to equip lifeboats or lifeboats on board ships or aircraft as safety equipment. Today there are models that are also available for civil use in exploration activities for example. To force water through the osmotic membrane, the pressure is provided by a hand-operated pump, equipped with a foldable lever for easy transport. These devices can obtain very small quantities of drinking water from seawater or from other sources of doubtful potability even in desert areas or brackish water wells.
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