419Glossary........................................
A
ABSENCE OF OXYGEN: The complete absence of oxygen in water described as Anaerobic.
ABSOLUTE ZERO: A theoretical condition concerning a system at zero Kelvin where a system
does not emit or absorb energy (all atoms are at rest).
ACCURACY: How close a value is to the actual or true value; also see precision. How closely an
instrument measures the true or actual value.
ACID AND BASE ARE MIXED: When an acid and a base are mixed, an explosive reaction
occurs and decomposition products are created under certain conditions.
ACID ANHYDRIDE: A compound with two acyl groups bound to a single oxygen atom.
ACID DISSOCIATION CONSTANT: An equilibrium constant for the dissociation of a weak acid.
ACID RAIN: A result of airborne pollutants.
ACID: Slowly add the acid to water while stirring. An operator should not mix acid and water or
acid to a strong base.
ACTINIDES: The fifteen chemical elements that are between actinium (89) and lawrencium (103).
ACTIVATED CARBON FILTRATION: Can remove organic chemicals that produce off-taste and
odor. These compounds are not dangerous to health but can make the water unpleasant to drink.
Carbon filtration comes in several forms, from small filters that attach to sink faucets to large
tanks that contain removable cartridges. Activated carbon filters require regular maintenance or
they can become a health hazard.
ACTIVATED CHARCOAL (GAC or PAC): Granular Activated Charcoal or Powered Activated
Charcoal. Used for taste and odor removal. A treatment technique that is not included in the
grading of a water facility.
ACTIVATED COMPLEX: A structure that forms because of a collision between molecules while
new bonds are formed.
ACTIVATION ENERGY: The minimum energy that must be input to a chemical system.
ADDITION REACTION: Within organic chemistry, when two or more molecules combine to make
a larger one.
ADSORPTION CLARIFIERS: The concept of the adsorption clarifier package plant was
developed in the early 1980s. This technology uses an up-flow clarifier with low-density plastic
bead media, usually held in place by a screen. This adsorption media is designed to enhance the
sedimentation/clarification process by combining flocculation and sedimentation into one step. In
this step, turbidity is reduced by adsorption of the coagulated and flocculated solids onto the
adsorption media and onto the solids already adsorbed onto the media. Air scouring cleans
adsorption clarifiers followed by water flushing. Cleaning of this type of clarifier is initiated more
often than filter backwashing because the clarifier removes more solids. As with the tube-settler
type of package plant, the sedimentation/ clarification process is followed by mixed-media
filtration and disinfection to complete the water treatment.
ADSORPTION: Not to be confused with absorption. Adsorption is a process that occurs when a
gas or liquid solute accumulates on the surface of a solid or a liquid (adsorbent), forming a film of
molecules or atoms (the adsorbate). It is different from absorption, in which a substance diffuses
into a liquid or solid to form a solution. The term sorption encompasses both processes, while
desorption is the reverse process. Adsorption is present in many natural physical, biological, and
chemical systems, and is widely used in industrial applications such as activated charcoal,
synthetic resins, and water purification.
AERATION: The mixing of air into a liquid or solid.
AGGLOMERATION: A jumbled cluster or mass of varied parts. The act or process of
agglomerating.
AIR ENTRAINMENT: The dissolution or inclusion of air bubbles into water.
AIR GAP SEPARATION: A physical separation space that is present between the discharge
vessel and the receiving vessel; for an example, a kitchen faucet.
AIR HOOD: The most suitable protection when working with a chemical that produces dangerous
fumes.