Glossary of Terms - A
A B C D E F G H I J K L M N O P Q R S T U V W Z
absorbent - A material, usually a porous solid, which takes another material into its interior. When rain soaks into soil, the soil is an absorbent.
absorption - The process in which one substance actually penetrating into the structure of another substance. This is different from adsorption in which one substance adheres to the surface of another.
acid - A substance which releases hydrogen ions when dissolved in water. Most acids will dissolve the common metals and will react with a base to form a neutral salt and water. An acid is the opposite of an alkali, has the pH rating lower than 7.0, will turn litmus paper red, and has a sour taste.
acidity - The quantitative capacity of water or solution to neutralize an alkali or base. It is usually measured by titration with a standard solution of sodium hydroxide and expressed in ppm or mg/L of calcium carbonate equivalent.
acre-foot - The volume of water which would cover an area of one acre to a depth of one foot. It is equal to 43,560 cubic feet (1,233 cubic meters) or 325,851 gallons (1,233,L).
activated alumina - A mineral made by treating aluminum ore so that it becomes porous and highly adsorptive. Activated alumina will remove several contaminants including fluoride, arsenic, and selenium. This activated carbon medium requires periodic cleaning with the appropriate regenerant such as alum, acid, and/or caustic.
activated carbon - A granular material usually produced by roasting various grades of coal in the absence of air. It has a very porous structure and it is used in water conditioning as an adsorbent for organic matter and certain dissolved gases. Sometimes called "activated charcoal".
activated silica - A material usually formed from the reaction of a dilute silicate solution with a dilute acid. It is used as a coagulant aid.
adsorbent - A material, usually solid, capable of holding gases, liquids and/or suspended matter at its surface and in exposed pores. Activated carbon and activated alumina are common adsorbents used in water treatment.
adsorption - The process in which matter adheres to the surface of an adsorbent.
aeration - The process in which air is brought into intimate contact with water, often by spraying water through air, or by bubbling air through water. Aeration may be used to add oxygen to the water for the oxidation of matter such as iron, or to cause the release of dissolved gases such as carbon dioxide or hydrogen sulfide from the water.
aerobic - An action or process conducted in the presence of air, such as aerobic digestion of organic matter by bacteria.
aggregate – A mass or cluster of soil particles, often having a characteristic shape.
air check – A device which allows water, but not air, to pass through it. An air check is a typical component of a water treatment system using a regenerant educator.
air gap - A clear vertical space between a water or drain line and the flood level of a receptacle to prevent back-flow or siphoning from the receptacle in the event of negative pressure or vacuum. Most plumbing codes require the air gap to be at least twice the diameter of the water or drain line, with a minimum of 1-1/2 inches (3.8 cm). (See vacuum breaker or back-flow preventer.)
air stripping - A technique of aeration for the removal of dissolved gasses and volatile substances, often pesticides of hydrocarbon products in water supplies. Large volumes of air are bubbled through the water to remove (strip out) the dissolved gases and volatile substances.
algae - Small primitive plants containing chlorophyll, commonly found in surface water. Excessive growths may create taste and odor problems, and consume dissolved oxygen during decay.
alkali - A substance which creates a bitter taste and a slippery feel when dissolved in water, and will turn litmus paper blue. An alkali has a pH greater than 7.0 and is the opposite of an acid. High alkali waters tend to cause drying of the skin. (See alkalinity, base.)
alkalinity - 1. The quantitative capacity of water to neutralize an acid; that is, the measure of how much acid can be added to a liquid without causing a significant change in pH. Alkalinity is not the same as pH because water does not have to be strongly basic (high pH) to have high alkalinity.
In the water industry, alkalinity is expressed in mg/L of equivalent calcium carbonate.
The following chemical equilibrium equations show the relationships among the three kinds of alkalinity: carbonate (CO32-), bicarbonate (HCO3-), and hydroxide alkalinity (OH-). Total alkalinity is the sum of all three kinds of alkalinity.
CO2 + H2O <===> H2CO3 <===> H+ + HCO3- <===> pH 4.5 pH 8.3 2H+ + CO32-
Above pH 9.5 (usually well above pH 10), OH- alkalinity can exist or CO32- and OH- alkalinities can coexist together. Different tests are used to determine the quantity of the different kinds of alkalinities present in water.
2. A property of water soluble substances (or mixtures) causing the concentration of hydroxyl ions (OH-) in water solutions to be higher than the concentration of hydrogen ions (H+). Alkalinity is exhibited in solution by alkalies such as sodium hydroxide and by alkaline salts such as sodium carbonate.
Soap and soap-based products are alkaline, since soap is a moderately alkaline salt and performs well only in an alkaline medium. Detergent products can be formulated with any desired level of alkalinity as dictated by the needs of the cleaning tasks to be performed.
Since the alkalinity is useful in removing acidic, fatty, and oily soils, most detergents are more effective on laundry soils when on the alkaline side. Generally, alkalinity is supplied to laundry detergents by builders.
All automatic dishwasher detergents utilize alkalinity, as do most cleansers and hard surface cleaners. In contrast, most hand dishwashing detergents are close to neutrality, performing efficiently without alkalinity because of the mechanical action of hand rubbing with sponge or dishcloth. (See alkali, base.)
alkyl benzene sulfonate (ABS) - A term applied to a family of branched chain chemical compounds, formerly used as detergents,. Sometimes called "hard" detergents, because of their resistance to biological degradation, these compounds have been largely replaced with linear alkyl sulfonate (LAS) which are more readily degraded to simpler substances. (See detergent, linear alkyl sulfonate.)
alum - A common name for aluminum sulfate, used as a coagulant in water treatment.
amoeba - A small, single-celled animal or protozoan which is widely found in fresh and salt water.
anaerobic - A condition in which there is no air or no available free oxygen.
An action or process conducted in the absence of air, such as the anaerobic digestion of organic matter by bacteria in a septic tank.
anaerobic organism - An organism that can thrive in the absence of oxygen (air), such as bacteria in a septic tank.
angstrom unit - A unit of length equal to one ten-billionth of a meter.
anion - An ion with a negative charge. An anion [such as chloride (Cl-), nitrate (NO3-), bicarbonate (HCO3-), or sulfate (SO42-] may result from the dissociation of salt, acid, or alkali.
anion exchange - An ion exchange process in which anions in solution are exchanged for other anions from an ion exchanger. In demineralization, for example, bicarbonate, chloride and sulfate anions are removed from solution in exchange for a chemically equivalent number of hydroxide anions from the anion exchange resin. (See ion exchange, demineralization.)
anode - The positive pole of an electrolytic system; also the metal which goes into solution in a galvanic cell. Sacrificial anodes made of metals such as magnesium, aluminum or zinc are sometimes installed in water heaters or other tanks to deliberately establish galvanic cells to control corrosion of the tank through the sacrifice of the anode.
aquifer - A natural water-bearing geological formation which is found below the surface of the earth.
artesian (aquifer or well) – Water held under pressure in porous rock or soil confined by impermeable geologic formations. An artesian well is free flowing.
atom - The smallest particle of an element that can exist either alone or in combination.
attrition - In water treatment, the process in which solids are worn down or ground down by friction, often between particles of the same material. Filter media and ion exchange materials are subject to attrition during backwashing, regeneration and service.
automatic water softener (or automatic filter) - A water softener (or filter) that is equipped with a clock timer which automatically initiates the backwash and/or the regeneration process at preset intervals of time.