437NTU (Nephelometric turbidity unit): A measure of the clarity or cloudiness of water.
NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY: Technique that exploits the magnetic
properties of certain nuclei, useful for identifying unknown compounds.
NUCLEAR: Of or pertaining to the atomic nucleus.
NUCLEUS: The center of an atom made up of neutrons and protons, with a net positive charge.
NUMBER DENSITY: A measure of concentration of countable objects (atoms, molecules, etc.) in
space; number per volume.
O
O3: The molecular formula of ozone.
OLIGOTROPHIC: A reservoir that is nutrient-poor and contains little plant or animal life. An
oligotrophic ecosystem or environment is one that offers little to sustain life. The term is
commonly utilized to describe bodies of water or soils with very low nutrient levels. It derives
etymologically from the Greek oligo (small, little, few) and trophe (nutrients, food). Oligotrophic
environments are of special interest for the alternative energy sources and survival strategies
upon which life could rely.
ORBITAL: May refer to either an atomic orbital or a molecular orbital.
ORGANIC CHEMISTRY: A part of chemistry concerned with organic compounds.
ORGANIC COMPOUND: Compounds that contain carbon.
ORGANIC PRECURSORS: Natural or man-made compounds with chemical structures based
upon carbon that, upon combination with chlorine, leading to trihalomethane formation.
OSMOSIS: Osmosis is the process by which water moves across a semi permeable membrane
from a low concentration solute to a high concentration solute to satisfy the pressure differences
caused by the solute.
OXIDE: An oxide is a chemical compound containing at least one oxygen atom as well as at least
one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are
oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon,
carbon monoxide and carbon dioxide. Even materials that are considered to be pure elements
often contain a coating of oxides. For example, aluminum foil has a thin skin of Al2O3 that
protects the foil from further corrosion.
OXIDIZING: The process of breaking down organic wastes into simpler elemental forms or by
products. Also used to separate combined chlorine and convert it into free chlorine.
OXYGEN DEFICIENT ENVIRONMENT: One of the most dangerous threats to an operator upon
entering a manhole.
OZONE DOES NOT PROVIDE A RESIDUAL: One of the major drawbacks to using ozone as a
disinfectant.
OZONE, CHLORINE DIOXIDE, UV, CHLORAMINES: These chemicals may be used as
alternative disinfectants.
OZONE: Ozone or trioxygen (O3) is a triatomic molecule, consisting of three oxygen atoms. It is
an allotrope of oxygen that is much less stable than the diatomic O2. Ground-level ozone is an air
pollutant with harmful effects on the respiratory systems of animals. Ozone in the upper
atmosphere filters potentially damaging ultraviolet light from reaching the Earth's surface. It is
present in low concentrations throughout the Earth's atmosphere. It has many industrial and
consumer applications. Ozone, the first allotrope of a chemical element to be recognized by
science, was proposed as a distinct chemical compound by Christian Friedrich Schönbein in
1840, who named it after the Greek word for smell (ozein), from the peculiar odor in lightning
storms. The formula for ozone, O3, was not determined until 1865 by Jacques-Louis Soret and
confirmed by Schönbein in 1867. Ozone is a powerful oxidizing agent, far better than dioxygen. It
is also unstable at high concentrations, decaying to ordinary diatomic oxygen (in about half an
hour in atmospheric conditions):2 O3 = 3 O2.
P
PAC: A disadvantage of using PAC is it is very abrasive and requires careful maintenance of
equipment. One precaution that should be taken in storing PAC is that bags of carbon should not
be stored near bags of HTH. Removes tastes and odors by adsorption only. Powered activated
carbon frequently used for taste and odor control because PAC is non-specific and removes a