Operation and Maintenance Manual for

APPENDIX LC Manual 11/02 Rev. 3
7.1 GLOSSARY OF TERMS
7.0 APPENDIX
The terms commonly used in reverse osmosis are defined below:
ANION - Negatively charged ion, such as CO3 -- , SO4 -- , HCO3 -- , Cl - , NO3 - , etc.
CATION - Positively charged ion, such as Ca ++ , Mg ++ , Fe ++ , Na + , K + , etc.
CONCENTRATE (REJECT) - Concentrated portion of the feed remaining outside the
membrane which is discarded.
CONDUCTIVITY - A measure of salt concentration due to the ability of dissolved solids (ions) to
conduct electricity, usually expressed as micromhos/cm.
FEED - The feedwater pumped into a permeator under high-pressure.
OSMOSIS - Osmosis is the diffusion of a solvent (such as pure water) from a dilute saline
solution into a more concentrated saline solution through a semipermeable membrane
separating the two solutions.
OSMOTIC HEAD - Osmotic head (pressure) is the change in head resulting from water
transport through the semipermeable membrane separating two saline solutions of different
concentrations.
PASSAGE - Ratio of permeate to feed concentration of a particular dissolved material,
expressed in percent.
PERMEATE (PRODUCT) - The purified portion of the feed passing through the membrane.
RECOVERY - Percent of feedwater converted into permeate.
REVERSE OSMOSIS (RO) - The process by which incoming fluid (feed) is forced under highpressure
through a reverse osmosis membrane. A portion of the fluid with concentrated ionic
materials (concentrate) remains upstream of the membrane and is discarded (unless it is of
interest in a particular application). The highly purified portion (permeate) which passed through
the membrane would then be collected for use (as in a water purification application).
REVERSE OSMOSIS (RO) MEMBRANE - An RO membrane is a semipermeable membrane
generally in sheet or hollow fiber form which rejects not only dissolved materials, but also
organics, submicron size colloidal materials and bacteria which may contaminate a high purity
USFilter 7-1