The answer should be around 31.25mg/L 2 Federal legislation states that \"At lea

Question

The answer should be around 31.25mg/L

2 Federal legislation states that "At least 99.9% (3-logs) removal and/or inactivation of Giardia lamblia and 99.99% (4-logs) removal and/or inactivation of viruses" is achieved for all surface water treatment. The system use a disinfection basin with a residence time of 4 min. The temperature is 15°C. What will be the total chlorine dose needed to ensure the water reach its disinfection target if the water chlorine demand fromm inorganics is 1.5 mg/L. CT values for virus and Giardia inactivation by_chlorine (and others) at a temperature of 15°C Giardia inactivation Tahle 2 C-T Values for Inactivation of Viruses 2-log 4-log 3-log Inactivation InactivationInactivation Disinfeetant nactivation 0.5 1.0 20 Chlonne Chloramine 40 79 119 643 067 1491 Ozone CT Vaues ( mg-mi/) CT Values obtained 2.0 2.5 3.0 0.5 B(USEPA 199

Explanation / Answer

From the given tables,

Dosage of chlorine required for Giardia inactivation (3-log level) = 119 mg-min/L
Dosage of chlorine required for 4-log virus inactivation = 6 mg-min/L

For a 4 minute detention period,
Chlorine demand = (119+6)*4 mg/L = 31.25 mg/L

Inorganic chlorine demand = 1.5 mg/L

Hence, total chlorine dosage required = 31.25 +1.5 = 32.75 mg/L

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