Giardia is a very common contaminant of surface waters, and one of the pathogens most likely to infect the careless backpacker. However, it can be inactivated with free chlorine, which can be easily added to a water bottle in the form of solid calcium hypochlorite tablets, Ca(OCl)2. In order to safely disinfect a 15 C water supply contaminated with Giardia, using free chlorine as a disinfectant, we must provide a Ct value of at least 75 (mg*min)/L (as Cl2). (a) First, what concentration of free chlorine (in mg/L as Cl2) is required to achieve this Ct for a contact time of 10 minutes? (b) How much Ca(OCl)2 (in mg of solid) would we have to add to a Nalgene bottle containing 1 L of the contaminated water to provide this concentration of free chlorine? Assume that each mole of Ca(OCl)2 yields 2 moles of HOCl when dissolved in water, and that the molecular weight of Ca(OCl)2 is approximately 143 g/mole. (c) If the second-order inactivation rate constant, k, for the reaction of Giardia with HOCl is 0.092 L/(mg*min), how many logs of inactivation should we be able to achieve in a PFR for the targeted Ct value?