438broad range of compounds. Jar tests and threshold odor number testing determines the
application rate for powdered activated carbon. Powdered activated carbon, or PAC, commonly
used for in a water treatment plant for taste and odor control. Powdered activated carbon may be
used with some success in removing the precursors of THMs.
PACKING: Material, usually of woven fiber, placed in rings around the shaft of a pump and used
to control the leakage from the stuffing box.
PARAMECIUM: Paramecia are a group of unicellular ciliate protozoa formerly known as slipper
animalcules from their slipper shape. They are commonly studied as a representative of the
ciliate group. Simple cilia cover the body which allows the cell to move with a synchronous
motion (like a caterpilla). There is also a deep oral groove containing inconspicuous compound
oral cilia (as found in other peniculids) that is used to draw food inside. They generally feed upon
bacteria and other small cells. Osmoregulation is carried out by a pair of contractile vacuoles,
which actively expel water absorbed by osmosis from their surroundings. Paramecia are
widespread in freshwater environments, and are especially common in scums. Paramecia are
attracted by acidic conditions. Certain single-celled eukaryotes, such as Paramecium, are
examples for exceptions to the universality of the genetic code (translation systems where a few
codons differ from the standard ones).
PATHOGENS: Disease-causing pathogens; waterborne pathogens A pathogen may contaminate
water and cause waterborne disease.
Pb: The chemical symbol of Lead.
PCE: Perchloroethylene. Known also as perc or tetrachloroethylene, perchloroethylene is a
clear, colorless liquid with a distinctive, somewhat ether-like odor. It is non-flammable, having no
measurable flashpoint or flammable limits in air. Effective over a wide range of applications,
perchloroethylene is supported by closed loop transfer systems, stabilizers and employee
exposure monitoring.
pCi/L: Picocuries per liter A curie is the amount of radiation released by a set amount of a certain
compound. A picocurie is one quadrillionth of a curie.
PERKINESIS: The aggregation resulting from random thermal motion of fluid molecules.
PEAK DEMAND: The maximum momentary load placed on a water treatment plant, pumping
station or distribution system.
PEPTIDOGLYCAN: A polymer found in the cell walls of prokaryotes that consists of
polysaccharide and peptide chains in a strong molecular network. Also called mucopeptide,
murein.
PERMEATE: The term for water which has passed through the membrane of a reverse osmosis
unit.
pH OF SATURATION: The ideal pH for perfect water balance in relation to a particular total
alkalinity level and a particular calcium hardness level, at a particular temperature. The pH where
the Langelier Index equals zero.
pH: A unit of measure which describes the degree of acidity or alkalinity of a solution. The pH
scale runs from 0 to 14 with 7 being the mid-point or neutral. A pH of less than 7 is on the acid
side of the scale with 0 as the point of greatest acid activity. A pH of more than 7 is on the basic
(alkaline) side of the scale with 14 as the point of greatest basic activity. The term pH is derived
from “p”, the mathematical symbol of the negative logarithm, and “H”, the chemical symbol of
Hydrogen. The definition of pH is the negative logarithm of the Hydrogen ion activity. pH=-
log[H+].
PHENOL RED: Chemical reagent used for testing pH in the range of 6.8 - 8.4.
PHENOLPHTHALEIN/TOTAL ALKALINITY: The relationship between the alkalinity constituent’s
bicarbonate, carbonate, and hydroxide can be based on the P and T alkalinity measurement.
PHOSPHATE, NITRATE AND ORGANIC NITROGEN: Nutrients in a domestic water supply
reservoir may cause water quality problems if they occur in moderate or large quantities.
PHOTON: A carrier of electromagnetic radiation of all wavelength (such as gamma rays and radio
waves).
PHYSISORPTION: (Or physical adsorption) Is adsorption in which the forces involved are
intermolecular forces (van der Waals forces) of the same kind as those responsible for the
imperfection of real gases and the condensation of vapors, and which do not involve a significant