deionization – The removal of all ionized minerals and salts (both cationic and anionic) from a solution by a two-phase ion exchange procedure. First, positively charged for a chemically equivalent amount of hydrogen ions. Second, negatively charged ions are removed by an anion exchange resin for a chemically equivalent amount of hydroxide ions. The hydrogen and hydroxide ions introduced in this process unite to form water molecules. The term is often used interchangeably with demineralization.
demineralization – The removal of ionized inorganic minerals and salts (not organic materials) from a solution by a two-phase ion exchange procedure; similar to deionization, and the two terms are often used interchangeably.
D.I. or DI – Abbreviation for “deionization”.
disinfection – A process in which pathogenic (disease producing bacteria) are killed; may involve disinfecting agents such as chlorine, or physical processes such as heating.
dissolved solids – The weight of matter in true solution in a stated volume of water; includes both inorganic and organic matter; usually determined by weighing the residue after evaporation of the water at 105 or 180 degrees Celcius.
distillation – The process in which a liquid, such as water, is converted into its vapor state by heating, and the vapor cooled and condensed to the liquid state and collected; used to remove solids and other impurities from water, multiple distillations are required for extreme purity.
equivalent per million – A unit of concentration used in chemical calculations, calculated by dividing the concentration in ppm or mg/1 by the equivalent weight.
exhaustion – The state of an ion exchange material in which it is no longer capable of effective function due to the depletion of the initial supply of exchangeable ions; the exhaustion point may be defined in terms of a limiting concentration of matter in the effluent, or in the case of demineralization, in terms of electrical conductivity.
filter – Specifically, a device or system for the removal of solid particles (suspended solids); in general, includes mechanical, adsorptive, oxidizing and neutralizing filters.
flocculation – The agglomeration of finely divided suspended solids into larger, usually gelatinous, particles; the development of a “floc” after treatment with a coagulant by gentle stirring or mixing.
flow control – A device designed to limit the flow of water or regenerant to a predetermined value over a broad range of inlet water pressures.
flow rate – The quantity of water or regenerant which passes a given point in a specified unit of time, often expressed in gallons per minute.
fluoridation – The addition of a fluoride compound to a water supply to produce the concentration desired for the reduction in incidence of dental caries.
fouling – The process in which undesirable foreign matter accumulates in a bed of filter media or ion exchanger, clogging pores and coating surfaces and thus inhibiting or retarding the proper operation of the bed.
freeboard – The vertical distance between a bed of filter media or ion exchange material and the over flow or collector for backwash water; the height above the bed of granular media available for bed expansion during backwashing; may be expressed either as a linear distance or a percentage of bed depth.