A unit for measuring the volume of water. One acre-foot equals 326,000 gallons.

Biocide

A chemical used to kill biological organisms, e.g. chlorine. 

 Brine.

Water that contains a high concentration of salt. Brine discharges from desalination plants may include constituents used in pretreatment processes, in addition to the high salt concentration seawater.

Capacity Factor

An electric utility's annual capacity factor is defined as the annual kilowatt-hour sales divided by the product of the total hours in a year and the rated capacity of the utility in kilowatts.

Coagulation

A pretreatment process in desalination plants. A substance, (e.g.,ferric chloride), is added to a solution to cause certain elements to become thickened into a coherent mass, so that they may be removed.

A process of desalination whereby an electrical current is used to separate out salt and impurities in the intake water. Most of the impurities in water are present in an ionized (electrically charged) state and will conduct electric current. When high voltage is applied, the impurities migrate towards the positive and negative electrodes, and the intermediate area becomes purified product water. This technology is used for brackish waters, but is not currently available for desalting seawater on a commercial scale.

Ion exchange

A pretreatment process in desalination plants. An electrical charge is used to remove charged particles from solution.

Kilowatt

(kV&127; One thousand watts. The watt is a measure of power used by electricity generating plants. One watt is equivalent to 1 Joule/second or 3.412 BTU/hour.

Multi-effect Distillation (MED)

A form of distillation. Evaporators are in series, and vapor from one series is used to evaporate water in the next one. This technology is in several forms, one of the most common of which is the Vertical Tube Evaporator (VTE).

Multi-stage Flash (MSF)

A form of distillation. The intake water is pressurized and heated. It is discharged into a chamber maintained slightly below the saturation vapor pressure of the water, and a fraction of the water content flashes into steam. The steam condenses on the exterior surface of heat transfer tubing and becomes product water. The unflashed brine enters a second chamber, where brine flashes to steam at a lower temperature. Each evaporation and condensation series is called a stage.

Reverse Osmosis (RO)

A process of desalination where pressure is applied to the feedwater, forcing the water molecules through a semipermeable membrane. The water that has passed through the membrane leaves the unit as product water, and most of the dissolved impurities remain behind and are discharged in a waste stream.

Scaling

Salt deposits on the interior surfaces of a desalination plant.

Total dissolved solids (tds)

Total salt and calcium carbonate concentration in a sample of water. The state recommended Maximum Contaminant Level (MCL) drinking water standard for total dissolved solids is 500 ppm. The upper MCL is 1,000 ppm, and the short-term permitted level is 1,500 ppm.

Vacuum Freezing (VF) `

A process of desalination where the temperature and pressure of the sea water is lowered so that the pure water forms ice crystals. The ice is then washed and melted to produce the product water. This technology is still being developed, and is not yet commercially competitive.

Vapor Compression (VC)