Environmental Engineering Reference
In-Depth Information
Visual Methods
The Octet Comparator uses standards that are mounted in a plastic compara-
tor block. It employs eight permanent translucent color standards and built-
in filters to eliminate optical distortion. The sample is compared using either
of two viewing windows. Two devices that can be used with the comparator
are a B-Color Reader, which neutralizes color or turbidity in water samples,
and an axial mirror, which intensifies faint colors of low concentrations for
easy distinction.
electronic Methods
Although the human eye is capable of differentiating color intensity, inter-
pretation is quite subjective. Electronic colorimeters consist of a light source
that passes through a sample and is measured on a photodetector with an
analog or digital readout. In addition to electronic colorimeters, specific
electronic instruments are manufactured for lab and field determination of
many water quality factors, including pH, total dissolved solids, conductiv-
it y, dissolved oxygen, temperature, and t u r bid it y.
Dissolved oxygen and Biochemical oxygen Demand*
A stream system used as a source of water produces and consumes oxygen.
It gains oxygen from the atmosphere and from plants as a result of photosyn-
thesis, and the churning of running water results in more dissolved oxygen
than is found in still water (e.g., in a reservoir behind a dam). Oxygen is
consumed by respiration by aquatic animals, decomposition, and various
chemical reactions.
Oxygen is actually poorly soluble in water. Its solubility is related to pres-
sure and temperature. In water supply systems,
dissolved oxygen
(DO) in raw
water is considered the necessary element to support life of many aquatic
organisms. From the drinking water practitioner's point of view, DO is an
important indicator of the water treatment process and an important factor
i in c or r o s iv it y.
Wastewater from sewage treatment plants often contains organic materials
that are decomposed by microorganisms, which use oxygen in the process.
The amount of oxygen consumed by these organisms in breaking down the
*
In this section and the sections that follow, we discuss several water quality factors that are
routinely monitored in drinking water operations. We do not discuss the actual test proce-
dures to analyze each water quality factor; instead, we refer readers to the latest edition of
Standard Methods
for the appropriate procedures to use in conducting these tests.
