Water and Wastewater Terms Beginning R

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reverse osmosis (RO)

A high-pressure membrane technology that applies pressure to a concentrated solution that causes the liquid to pass across a semipermeable membrane to a weaker solution. The membrane allows the passage of the water (solvent) but not the dissolved solids (solutes) to seperate particles of 0.0001-microns to over 0.001-microns diameter or more from influent. RO can remove dissolved metal ions and dissolved salts. This process operates at high pressures because the principal mechanism of seperation is diffusion, rather than sieving. Also see osmosis.