[10 points] The chlorine demand curve on the graph was obtained for a drinking water as below. Determine the dose of chlorine to produce a free residual of 0.7 mg/L.
(source: Theory and Practice of Water and Wastewater Treatment, Ronald Droste, 1997, Wiley Inc.)
[10 points in total] Disinfection of the lake water is required for 4 log virus inactivation (99.99 percent inactivation). The lake water does not provide adequate natural disinfection based on site evaluation by the state authority, and here is the CT value table required for inactivation of viruses at various temperature and pH.
unit: (mg/l)·min
The transmission main from the water treatment plant (receiving lake water) to the first customer is 2.5 miles, the maximum pumping rate is 8.0 ft/s, water temperature is 10◦C, and pH is 6.5.
[5 points] If chlorine is applied at the water treatment plant, what is required minimum chlorine concentration for 4 log virus inactivation (99.99 percent)? (1 mile = 5,280 ft)
[5 points] Calculate CT value if the state authority were to require the water entering the distribution system to have a residual of 0.4 mg/L. Is it adequate for 4 log virus inactivation (99.99 percent) at 0.5◦C?
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