Q15. When taking samples from a standing water
supply, you take the samples from how far below
the surface and at what angle?
TREATMENT CONTROL TEST
PROCEDURES
LEARNING OBJECTIVE: Understand
procedures and analysis for different types of
water tests.
Various analyses of water must be performed by
trained chemists or skilled laboratory technicians. As a
Utilitiesman, however, you must be able to perform
various types of treatment control tests. These tests are
used during treatment to ensure proper operation and
the output of safe water of acceptable quality. We will
describe the procedures to follow in carrying out a
number of treatment processes, such as chlorination,
corrosion control, and clarification.
Before proceeding, note that certain tests which
we will cover are based on the simple principle of
adding a chemical to the sample that forms a color with
the substance to be measured and matching the treated
sample with color standards containing known
amounts of the substance. There are several
colorimeter sets available commercially which vary
slightly in use and operation. For that reason, make a
careful study of the manufacturer’s instructions before
using such equipment. Other tests are performed by
titration or by special instruments. “Titration” means
finding out how much of a substance is in a given
solution by measuring how much of another substance
or reagent has to be added to the given solution to
produce a given reaction.
Various reagents required for the tests discussed
below are available from a number of manufacturers
and laboratory supply houses. Some of these reagents
require special preparation and handling before test
use. This is customarily the responsibility of the
laboratory technician, since, in some cases, the
preparation of reagents requires a thorough knowledge
of the chemical procedures. For complete information
on the preparation of reagents, refer to the
manufacturer’s instructions or consult your
supervising petty officer.
CHLORINE RESIDUALS
Two tests are frequently used in testing water for
chlorine resid uals. They are the orthotolidine test and
the orthotolidine-arsenite (OTA) test. Each of these
tests is discussed separately below.
Orthotolidine Test
Chlorine residuals can be measured easily by using
a commercial comparator and orthotolidine reagents.
EQUIPMENT.—Either
a
disk
or
slide
comparator may be used in performing the
orthotolidine test. A disk comparator is shown in
figure 7-13. This comparator consists of a standard
color disk and two sample tubes. Water to be tested is
placed in both tubes. Reagent is added to one and the
resulting color matched with the disk. The other tube is
placed behind the disk to eliminate any color error that
might be caused by turbidity in the test sample.
A slide comparator, also referred to as a block
comparator, is shown in figure 7-14. This comparator
consists of standard color ampoules for more accurate
color matching. The other two sample tubes are used as
compensators and are placed behind the color
ampoules.
— only reagent used is a standard orthotolidine
solution.
Figure 7-13.—Disk comparator with the front removed
show construction.
Figure 7-14.—Slide comparator for chlorine residual test.
7-19
