Table 7-5. - Optimum pH Ranges for Common Coagulants

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 gallons.

9. Repeat the steps for each chemical used until satisfactory results are obtained.

TURBIDITY TEST

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 tested.

2. The glass plunger is inserted in the tube.

3. The tube is placed in the instrument.

Figure 7-18. - Turbidimeter.

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.

RECORDS

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.