Glossary

This glossary includes terms and acronyms related to desalination and may or may not relate to the scwd2 Desalination Program.  This glossary is provided as a general reference tool. 

Acre-foot (AF). A unit for measuring the volume of water. One acre-foot equals 325,851 gallons (the volume of water that will cover one acre to a depth of one foot). One million gallons equals 3.07 acre-feet.

Bactericide. An agent capable of destroying bacteria.

Banked Water.  Water stored in the aquifer by reducing groundwater pumping (that could be extracted at a later time).

Brackish Water. In general, water having a total dissolved solids concentration ranging from about 1,000 to 10,000 mg/L.

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. Also referred to as concentrated salty water.

BTU (British Thermal Unit). A standard unit for measuring a quantity of thermal energy, either electricity, natural gas or any other source of energy. One Btu is the amount of thermal energy required to raise the temperature on one pound of water one degree Fahrenheit at sea level.

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

Cogeneration. A power plant that is designed to conserve energy by using "waste heat" from generating electricity for another purpose.

Concentrated salty water. See Brine

Desalting. A process that removes salts from feedwater. Same as Desalination.

Double-pass system. A RO or NF system in which the permeate is futher processed by a subsequent RO or NF unit.

Deaeration. Removal of oxygen. A pretreatment process in desalination plants to reduce corrosion.

Distillation. A process of desalination where the intake water is heated to produce steam. The steam is then condensed to produce product water with low salt concentration.

Electrodialysis. Most of the impurities in water are present in an ionized (electrically-charged) state. When an electric current is applied, the impurities migrate towards the positive and negative electrodes. The intermediate area becomes depleted of impurities and discharges a purified stream of product water. This technology is used for brackish waters but is not currently available for desalting seawater on a commercial scale.

Entrainment.  Passage of smaller marine organisms through the screen mesh of an intake system.

Feedwater. Water fed to the desalination equipment. This can be source water with or without pretreatment.

Flat sheet membrane. A membrane manufactured in a flat form. Commonly used in a spiral-wound membrane elements.

Fouling. The gradual accumulation of contaminants on a membrane surface or within a porous membrane structure that inhibits the passage of water, thus decreasing permeability.

gpd. Gallons per day.

Impingement.  Pinning of larger marine organisms on the screen mesh as water is drawn into the intake system.

Infiltration Gallery. A method used for seawater intake. Perforated pipes are arranged in a radial pattern in the sand onshore below the water level. Water in the saturated sand enters the perforated pipes.

Ion Exchange. A water treatment process. An electric charge is used to remove charged particles from solution.

Kilowatt (kW). A thousand watts. The watt is a measure of power used by electricity generating plants. One watt is equivalent to 1 Joule/second or 3.4127 Btu/hour.

Megawatt (MW). A million watts.

Membrane. A thin layer of material capable of separating materials as a function of their chemical or physical properties when a driving force is applied.

Microlayer. The upper few millimeters of the ocean. Fish eggs are sometimes concentrated in the microlayer.

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

MF. Microfilitration

Multistage Flash (MSF). A form of distillation. Intake water is heated then discharged into a chamber maintained slightly below the saturation vapor pressure of the incoming water, so that 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 another chamber at a lower pressure, where a portion flashes to steam. Each evaporation and condensation chamber is called a stage.

NF. Nanofiltration

Ocean Thermal Energy Conversion (OTEC). A solar, ocean thermal desalination approach where electricity is produced by using the temperature differential between cold, deep waters and warm, shallow surface waters. Water at the ocean surface (at about 70°F) is used to heat liquid ammonia, which vaporizes at this temperature in a vacuum chamber. The ammonia vapor is used to turn a turbine to produce electricity. The vapor is then condensed by using cold water pumped up from the ocean depths (at about 35°F).

Product Water. The desalted water delivered to the water distribution system. Also referred to as finish water or potable water.

Rationing.  Reducing water consumption (usually represented by a percentage of total water use.  example: 15%)

Recycled Water. Treated wastewater used for non-potable uses, such as irrigation.  The City of SC is currently using recycled water at the Wastewater Treatment Plant and Soquel Creek Water District is evaluating Satellite Reclamation Plants (SRPs) for large-irrigation users.

Reverse Osmosis (RO). A process of desalination where pressure is applied continuously to the feedwater, forcing water molecules through a semipermeable membrane. Water that passes through the membrane leaves the unit as product water; 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.

SCWD. City of Santa Cruz Water Department

scwd2. Task force established between the City of Santa Cruz and Soquel Creek Water District to oversee and evaluate a potential cooperative desalination program which may provide water during droughts and preserve groundwater aquifers for the communities from Santa Cruz to La Selva Beach and other areas that depend on these agencies for water.

SqCWD. Soquel Creek Water District

Stage. A set of pressure vessels installed in parallel.

SWRO. Seawater Reverse Osmosis. Used as the abbreviation for seawater using RO.

Total Dissolved Solids (tds). Total salt and calcium carbonate concentration in a sample of water, usually expressed in milligrams per liter (mg/L) or parts per million (ppm). The CA state-recommended Maximum Contaminant Level (MCL) drinking water standard for total dissolved solids is 500 mg/L, the upper MCL is 1,000 mg/L, and the short-term permitted level is 1,500 mg/L.

UF. Ultrafiltration

Vapor Compression Distillation (VCD). A form of distillation. A portion of feedwater is evaporated, and the vapor is sent to a compressor. Mechanical or thermal energy is used to compress the vapor, which increases its temperature. The vapor is then condensed to form product water and the released heat is used to evaporate the feedwater.

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