Problem 1. A potable water containing 104CFU/100ml of total Coliform will be disinfected using calcium hypochlorite Ca(OCl). The change of chlorine concentration by time for this potable water is given in Figure below. For the potable water, the inactivation of total coliform by chlorine obeys to Chick-Watson Law with n=1 and k=0.075L/mg.min. The daily flow rate of water to be disinfected is 15000m3/d. Design a chlorine disinfection tank with specifying dimensions based on a suitable contact time and determine initial and residual chlorine concentrations for 99.9% of disinfection efficiency. Finally, calculate daily amount of calcium hypochlorite required as kg/d for this disinfection process. Note that residual chlorine concentration should be greater than 0.75mg/L. (25p)