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The discovery and development of membrane water treatment processes (ultrafiltration, electrodialysis, and reverse osmosis) began in the 1920s, but these did not really become practical in water treatment for 40 years. Rapid technological developments of these processes have taken place since 1960, and today they are invaluable adjuncts to both water and waste treatment technology-yet all these membrane technologies, and more, are routinely performed by the human kidney.

Reverse osmosis provides a very important unit process for use by the present day point-of­use water treatment professional. Together with filtration and ion exchange, which can be used in pretreatment or post-treatment, reverse osmosis dramatically extends his expertise and really rounds out his technological capabilities.

The reverse osmosis rejection table demonstrates the ability and versatility of a reverse osmosis-activated carbon system at a water pressure of 50 psi.

First, such membranes constitute the finest particulate filter known, which is shown by the 100% removal of turbidity and the virtually 100% removal of asbestos.

They show an 88% removal of total dissolved solids, with corresponding substantial ability to remove many other cations and anions listed in the EPA Drinking Water Regulations from 30% removal for silver and 40% removal for nitrate to 98% removal for sulfate.

Likewise, the ability of RO/carbon to remove dissolved organics is exceptional.

In a paper by Hanes, Bratina, and Brown entitled, "Lead Removal in Home Water Purifiers," presented at the Annual Conference of the American Water Works Association, Atlantic City, New Jersey, June 27, 1978, the authors show that a reverse osmosis household unit operating at normal household water pressure reduced the lead level from an influent of 762 micrograms per liter to a mean lead concentration of 22 micrograms per liter (97% removal). Then, the activated carbon unit further reduced the 22 micrograms per liter RO effluent to a mean lead level of 5 micrograms per liter (99% removal for both reverse osmosis and activated carbon)

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