A regional city has a population of 30,000 people and a drinking water supply need of 220 L.person.day. Raw drinking water is to be treated by rapid sand filtration followed by free chlorine disinfection at pH 6. The chlorine disinfection process is designed to achieve 2.00 log10 reduction of Giardia lamblia cysts, requiring CT = 36.0 mg.L.min (as Cl) at the typical ambient water temperature of 20C. The chlorine contact tanks have a total volume of 140 m. Due to the presence of dissolved substances, the filtered water has an instantaneous chlorine demand of 2.30 mg/L. (a) Determine the chlorine contact time (5 marks) (b) Determine the required average free chlorine concentration (as Cl) in the chlorine contact tanks (5 marks) (c) Determine the free chlorine concentration (as Cl) that must be dosed to achieve the required average free chlorine concentration (5 marks) (d) If chlorine is supplied to the water from a cylinder of chlorine gas (Cl), determine the mass of chlorine gas consumed per day (5 marks)