Advanced Waterworks Mathematics, 2019a

Location and Type of
Disinfection
Treatment Plant
Pipeline
Actual CT Required CT CT Ratio
3.0 mg/L · min
712 mg/L · min
Treatment Plant Actual CT:
1.2 mg/L 35 min 42 mg/L min
Pipeline Actual CT:
0.4 mg/L 12 min 4.8 mg/L min
Now you can finish populating the table and calculating the CT Ratios.
Actual CT 42 mg/L min
= 14
Required CT 3.0 mg/L min
Actual CT 4.8 mg/L min
= 0.00674 = 0.0
Required CT 712 mg/L min
Location and Type of
Disinfection
Actual CT Required CT CT Ratio
Treatment Plant 42 mg/L · min 3.0 mg/L · min 14
Pipeline 4.8 mg/L · min 712 mg/L · min 0.0
Total: 14.0
Yes! This plant does meets compliance for CT inactivation of viruses.
8. Does a water utility meet CT for viruses by disinfection if only the free chlorine
concentration is 0.5 ppm through 200 ft of 24” diameter pipe at a flow rate of 730 gpm?
Assume the water is 15°C and has a pH of 8.0.
Pipeline:
From Table 7.2 Treatment Credits and Log Inactivation Requirements you can see that:
4 Log (Required) Pipeline Only – No credits
Now look at Table C-7 Inactivation of Viruses by Free Chlorine. The solution is where the
15°C column intersects with the 4 Log Inactivation row.
4.0 mg/L min CT is required.
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