Table 7-5.Optimum pH Ranges for Common
5.0 to 7.0
9.5 and above
4.0 to 6.5 and above 9.5
4.0 to 6.5 and above 9.5
4.0 to 10.0
3. Add 0.5 ml of standard coagulant solution to one
sample of raw water, 1.0 ml to the second sample, 2.0 ml to
the third sample, 3.0 ml to the fourth sample, 4.0 ml to the
fifth sample, and 5.0 ml to the sixth sample. The result is a
dosage of 5, 10, 20, 30, 40, and 50 mg/1, respectively.
4. Agitate samples in the jar test apparatus at a
velocity about equal to the treatment equipment you are
using and for the same length of time as the treatment
equipment mixing time.
5. Keep the samples at the same temperature as
water passing through your treatment equipment.
6. After stirring, let the samples settle for 30 minutes.
7. Siphon off a sample of the supernatant and
determine the turbidity by using a turbidimeter.
8. The smallest amount of coagulant that produces
the lowest turbidity represents the optimum dosage.
Multiply the coagulant dosage in mg/1 (step 5 above) by
8.33 to get the correct chemical feed in pounds per million
9. Repeat the steps for each chemical used until
satisfactory results are obtained.
Special instruments are available for measuring
turbidity (fig. 7-18). These instruments greatly simplify
the work of the operator performing a turbidity test.
Results are reliable and accurate. Complete instructions
are available from manufacturers of these instruments. In
general, however, the principles of operation are the
same. Usually an easy, five-step procedure is followed.
1. The sample tube is filled with the water to be
2. The glass plunger is inserted in the tube.
3. The tube is placed in the instrument.
4. The dial at the side of the instrument is turned until
the field seen in the eyepiece becomes uniform.
5. The value indicated on the dial is read and the
turbidity content of the sample being tested is determined
directly from a chart furnished with the instrument.
Results of all findings made in the laboratory
should be recorded on laboratory data forms. Two
forms for recording data are the Potable Water Supply
and Distribution Operating Record and the Potable
Water Treatment Plant Operating Record.
The Potable Water Supply and Distribution
Operating Record are designed as a management tool for
analysis of operating data and evaluation of the potable
water supply and distribution performance. Complete
instructions on the method of daily entries on this form
are on its reverse side.
The Potable Water Treatment Plant Operating
Record is designed as a management tool for the analysis
of operating data and the evaluation of potable water
treatment plant performance. A separate form should be
prepared for each potable water treatment plant at an
activity. Complete instructions on the method of daily
entries on this form are on its reverse side.