4. a) A proposed new drinking water treatment plant must provide 1.0-log Giardia

Question

4. a) A proposed new drinking water treatment plant must provide 1.0-log Giardia inactivation through disinfection. The plant will use free chlorine The water experiences an average temperature of 15°C and pH of 8.0 over the course of a year. The temperature ranges are from 0.5°C to 20°C, and pH 6.5 to 8.5. The anticipated flow rate will range from 10 MLD (million liters per day) to 25 MLD. The following table is from the Ontario regulations showing the CT required for 1.0-log Giardia inactivation as a function of temperature and pH: CT requirements (mg min/L) for 1.0-log Giardia inactivation 20 pH 6.5 pH 7.5 pH 8.5 0.5 20 40 60 10°C 10 20 30 10 15 Disinfection will be achieved in a clearwell, as shown below. Cl Cl, online monitor Clearwell to from filters distribution If it is assumed that the chlorine residual leaving the clearwell will always be at least 1.0 mg/L, how big must the clearwell be (m2)?

Explanation / Answer

in the worst case when water require is 25MLD and pH 8.5 TEMP 0.5 deg

CT= 60m 1 hr

flow in 1 hr = 25/24= 1.04167 Milion lit = 1041.67 m3 = volume required

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