Water Treatment Glossary
  • A

  • Absorption

    The passage of one substance into or through another; e.g., an operation in which one or more soluble components of a gas mixture are dissolved in a liquid.

  • Acclimatization

    The physiological and behavioral adjustments of an organism to changes in its environment.

  • 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.

  • Acid Deposition/Acid Rain

    A complex chemical and atmospheric phenomenon that occurs when emissions of sulfur and nitrogen compounds and other substances are transformed by chemical processes in the atmosphere, often far from the original sources, and then deposited on earth in either a wet or dry form. The wet forms, popularly called "acid rain," can fall as rain, snow, or fog. The dry forms are acidic gases or particulates.


    A granular material usually produced by the roasting of cellulose base substances, such as wood or coconut shells, in the absence of air. It has a very porous structure and is used in water conditioning as an adsorbent for organic matter and certain dissolved gases. Sometimes called "activated charcoal".

  • Adhesion

    Molecular attraction which holds the surfaces of two substances in contact.


    The process in which matter adheres to the surface of an adsorbent.

  • Adsorption

    1. Adhesion of molecules of gas, liquid, or dissolved solids to a surface. 2. An advanced method of treating wastes in which activated carbon removes organic matter from wastewater.

  • Advanced Waste Water Treatment

    Any treatment of sewage that goes beyond the secondary or biological water treatment stage and includes the removal of nutrients such as phosphorus and nitrogen and a high percentage of suspended solids. (See primary, secondary treatment.)

  • Aeration

    A process which promotes biological degradation of organic water. The process may be passive (as when waste is exposed to air), or active (as when a mixing or bubbling device introduces the air).

  • Aeration Tank

    A chamber used to inject air into water.

  • Agglomeration

    The process by which precipitation particles grow larger by collision or contact with cloud particles or other precipitation particles.

  • Algae

    Simple rootless plants that grow in sunlit waters in relative proportion to the amounts of nutrients available. They can affect water quality adversely by lowering the dissolved oxygen in the water. They are food for fish and small aquatic animals.


    The quantitative capacity of a water or water solution to neutralize an acid. It is usually measured by titration with a standard acid solution of sulfuric acid, and expressed in terms of its calcium carbonate equivalent.

  • Anaerobic

    A life or process that occurs in, or is not destroyed by, the absence of oxygen.


    A negatively charged ion in solution, such as bicarbonate, chloride or sulfate.


    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.


    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.

  • B


    The process in which beds of filter or ion exchange media are subjected to flow opposite to the service flow direction to loosen the bed and to flush suspended matter, collected during the service run, to waste.

  • Bacteria

    (Singular: bacterium) Microscopic living organisms which can aid in pollution control by consuming or breaking down organic matter in sewage. or by similarly acting on oil spills or other water pollutants. Bacteria in soil, water or air can also cause human, animal and plant health problems.

  • Baghouse Filter

    Large fabric bag, usually made of glass fibers, used to eliminate intermediate and large (greater than 20 microns in diameter) particles. This device operates in a way similar to the bag of an electric vacuum cleaner, passing the air and smaller particulate matter, while entrapping the larger particulates.

  • Bar Screen

    In wastewater treatment, a device used to remove large solids.

  • BASE

    A substance which releases hydroxyl ions when dissolved in water. Bases react with acids to form a neutral salt and water.

  • BED

    The exchange or filter media in a column or other tank or operational vessel.


    The height of the ion exchange or filter media in the vessel after preparation for service.

  • Biochemical Oxygen Demand (BOD)

    A measure of the amount of oxygen consumed in the biological processes that break down organic matter in water. The greater the BOD, the greater the degree of pollution.

  • Biodegradable

    The ability to break down or decompose rapidly under natural conditions and processes.

  • Biological Control

    In pest control, the use of animals and organisms that eat or otherwise kill or out-compete pests.

  • Brackish Water

    A mixture of fresh and salt water.


    A strong solution of salt (s), such as the sodium chloride brine used in the regeneration of ion exchange water softeners, but also applied to the mixed sodium, calcium and magnesium chloride waste solution from regeneration.