446TRANSITION METAL: Elements that have incomplete d sub-shells, but also may be referred to
as the d-block elements.
TRANSURANIC ELEMENT: Element with atomic number greater than 92; none of the
transuranic elements are stable.
TREATED WATER: Disinfected and/or filtered water served to water system customers. It must
meet or surpass all drinking water standards to be considered safe to drink.
TRIHALOMETHANES (THM): Four separate compounds including chloroform,
dichlorobromomethane, dibromochloromethane, and bromoform. The most common class of
disinfection by-products created when chemical disinfectants react with organic matter in water
during the disinfection process. See Disinfectant Byproducts.
TRIPLE BOND: The sharing of three pairs of electrons within a covalent bond (example N2).
TRIPLE POINT: The place where temperature and pressure of three phases are the same (Water
has a special phase diagram).
TUBE SETTLERS: This modification of the conventional process contains many metal tubes that
are placed in the sedimentation basin, or clarifier. These tubes are approximately 1 inch deep and
36 inches long, split-hexagonal shape and installed at an angle of 60 degrees or less. These
tubes provide for a very large surface area upon which particles may settle as the water flows
upward. The slope of the tubes facilitates gravity settling of the solids to the bottom of the basin,
where they can be collected and removed. The large surface settling area also means that
adequate clarification can be obtained with detention times of 15 minutes or less. As with
conventional treatment, this sedimentation step is followed by filtration through mixed media.
TUBERCLES: The creation of this condition is of the most concern regarding corrosive water
effects on a water system. Tubercles are formed due to joining dissimilar metals, causing electro-
chemical reactions. Like iron to copper pipe. We have all seen these little rust mounds inside
cast iron pipe.
TUNDALL EFFECT: The effect of light scattering by colloidal (mixture where one substance is
dispersed evenly through another) or suspended particles.
TURBIDIMETER: Monitoring the filter effluent turbidity on a continuous basis with an in-line
instrument is a recommended practice. Turbidimeter is best suited to perform this measurement.
TURBIDITY: A measure of the cloudiness of water caused by suspended particles.
U
U.S. ENVIRONMENTAL PROTECTION AGENCY: In the United States, this agency responsible
for setting drinking water standards and for ensuring their enforcement. This agency sets federal
regulations which all state and local agencies must enforce.
UN NUMBER: A four digit code used to note hazardous and flammable substances.
UNCERTAINTY: A characteristic that any measurement that involves estimation of any amount
cannot be exactly reproducible.
UNCERTAINTY PRINCIPLE: Knowing the location of a particle makes the momentum uncertain,
while knowing the momentum of a particle makes the location uncertain.
UNDER PRESSURE IN STEEL CONTAINERS: After chlorine gas is manufactured, it is primarily
transported in steel containers.
UNIT CELL: The smallest repeating unit of a lattice.
UNIT FACTOR: Statements used in converting between units.
UNIT FILTER RUN VOLUME (UFRV): One of the most popular ways to compare filter runs. This
technique is the best way to compare water treatment filter runs.
UNIVERSAL OR IDEAL GAS CONSTANT: Proportionality constant in the ideal gas law (0.08206
Lꞏatm/(Kꞏmol)).
V
VALENCE BOND THEORY: A theory explaining the chemical bonding within molecules by
discussing valencies, the number of chemical bonds formed by an atom.
VALENCE ELECTRON: The outermost electrons of an atom, which are located in electron shells.
VAN DER WAALS FORCE: One of the forces (attraction/repulsion) between molecules.
VAN’T HOFF FACTOR: Ratio of moles of particles in solution to moles of solute dissolved.
VANE: That portion of an impeller that throws the water toward the volute.