Water and Wastewater Terms Beginning R

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reverse osmosis (RO)

The application of pressure to a concentrated solution, which causes the passage of a liquid from the concentrated solution to a weaker solution across a semipermeable membrane. The membrane allows the passage of the water (solvent) but not the dissolved solids (solutes). In the RO process, two liquids are produced: the reject (containing high concentrations of dissolved solids) and the permeate (containing low concentrations). Also see osmosis.