The process takes advantage of the ability of certain natural and synthetic materials to exchange one of their ions.Ī number of naturally occurring minerals have ion exchange properties. It has also been used selectively to remove specific impurities and to recover valuable trace metals like chromium, nickel, copper, lead and cadmium from industrial waste discharges. This technique has been used extensively to remove hardness, and iron and manganese salts in drinking water supplies. Solvent extraction is also used to recover certain organic chemicals like phenol an d amines from industrial waste waters. For the removal of soluble organics from waste water the most commonly used method is adsorption on activated carbon. Three methods which are finding wide application in advanced waste treatment are ion-exchange, electro dialysis and reverse osmosis. A number of methods have been investigated for the removal of inorganic constituents from waste water. The dissolved solids are of both organic and inorganic types. Also the fouling rate is lower compared to Ro systems. Because nano filtration uses less fine membranes, the feed pressure of the NF system is generally lower compared to RO systems. This technique can be seen as a coarse RO (reversed osmosis) membrane. The nano filtration technique is mainly used for the removal of two valued ions and the larger mono valued ions such as heavy metals. The solution to be treated is passed through the membrane at a certain speed and under hydrostatic pressure, obtaining a concentrated fraction of oils and grease for disposal, while the filtrate is recovered and reused to prepare new baths. There has been a relatively recent application of this technique in the metal finishing sector for the recovery of degreasing baths (the first cleaning bath in metal-finishing processes, for pieces which are still dirty with lubricating substances). The single pass ultra filtering process is the simplest and most commonly used process for water treatment because it allows the recovery of high percentages of permeate (approximately 90-95 %). Ultra filtering systems generally work in a pressure range between 1.5 and 7 bar With industrial discharge waters the fluxes of permeate generally fluctuate between 0.5 and 1 – 5 m 3 / h / m 2 surface, depending on the concentration of the substances to be separated, with energy consumptions varying between 2 and 20 KWh per m3 of permeate. The selectivity depends on the membrane structure and is defined as the cut-off of molecular weight, which the membrane can separate with an efficiency of 90 % (although this definition may not be rigorous depending on the molecular shape)Ĭommercial membranes applied in ultra filtering can separate substances with a molecular weight between 1.000 and 10.000. The membranes used, polymeric or mineral, allow dissolved salts to pass while they reject high molecular weights selectively. This is a dynamic filtering process with a predominance of physical (mechanical) phenomena in which chemical phenomena are also involved.

Waste management treatment processes