ACTIVATED SLUDGE:  Sludge particles produced by the growth of organisms in the aeration tank in the presence of dissolved oxygen.

BACKFLOW PREVENTER:  A device on a water supply pipe to prevent the backflow of water into the water supply system from the connections on its outlet end.

CARBON ADSORPTION:  The use of either granular or powdered carbon to remove organic compounds from wastewater or effluents.

DEGASIFICATION:  (1) The removal of a gas from a liquid medium. (2) In water treatment, the removal of oxygen from water to inhibit corrosion.

EMULSION:  A heterogeneous liquid mixture of liquids not normally dissolved in one another, but held in suspension one in the other by forceful agitation or by emulsifiers that modify surface tension to prevent coalescence.

FALSE FILTER BOTTOM:  A type of under-drainage system consisting of a porous or perforated floor suspended above the true bottom of the filter.

GRIT:  The heavy suspended mineral matter present in water or wastewater, such as sand, gravel, or cinders.

HEAT TREATMENT:  A sludge conditioning process combining high temperature, time, and pressure to improve the dewaterability of organic sludge.

LIME:  Any of a family of chemicals consisting essentially of calcium hydroxide made from limestone (calcite) ; used to increase pH to promote precipitation reactions or for lime stabilization to kill parthenogenic organisms.

|MERCAPTANS:  Aliphatic organic compounds that contain sulfur. They are noted for their disagreeable odor.

PERIPHERAL WEIR:  The outlet weir extending around the inside of the circumference of a circular settling tank over which the effluent discharges.

RADIAL FLOW:  The direction of flow across a tank from center to periphery or vice versa.

THRESHOLD ODOR:  The minimum odor of the water sample that can barely be detected after successive dilutions with odorless water. Also called odor threshold.

UPFLOW:  Term used to describe treatment units in which flow enters at the bottom and exits at the top.

VAPORIZATION:  The process by which a substance such as water changes from the liquid or solid state to the gaseous state.

WATER COLUMN: (1) The water above the valve in a set of pumps. (2) A measure of head or pressure in a closed pipe or conduit.

Terms and definitions were abstracted from a glossary complied by the Water Environment Federation (WEF), a not-for-profit technical and educational organization of 36,000 individual members.