(12) 3. An engineer is designing a disinfection system that will rely on free chlorine as...

 

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(12) 3. An engineer is designing a disinfection system that will rely on free chlorine as the disinfectant for Giardia. They have measured a chlorine breakpoint curve (below) to ensure the correct amount of free chlorine is generated. 0.90 (1) (1) (1) (4) W 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 Chlorine dose(mg/L) 0.80 0.70 0.60 0.50 0.40 0,30 0.20 0.10 0.00 Using the graph above (Chlorine dose (mg/L) vs. total chlorine residual (mg/L)), answer the following: a) What is the concentration of readily oxidizable substances? b) What is the breakpoint chlorination dosage? c) What is the dominant form of chlorine when the chlorine dose is 0.6 mg/L or less? d) The engineer must ensure that at least 3-log inactivation of Giardia occurs at 20C. The pH of the system varies between 7.0 and 8.0. The The time of this clearwell with average baffling is known to be 50 min. What should the measured total residual chlorine be at the exit of the clearwell to ensure 3-log disinfection under the conditions described? (reported as mg/L) (5) e) The engineer is worried that plans to first coagulate the water using alum (Al2(SO4)14H0; molecular weight= 600 g/mol) will change the design of the disinfection system. If the alkalinity of the water were measured to be 20 mg/l as CaCOs, would the addition of 65 mg/L of alum change the required CT? Indicate if the required CT will increase, decrease or stay the same? Why? Show your calculations, refer to the reactions below, and the CT tables attached to the exam. You can assume that all alkalinity is in the form of HCO and both reactions go to completion. Al (50), 14H0 + 6H0-2A1(OH)2)+6H*+350 +14H0 HCO5 + HCO + HO Page 3 of 5 (12) 3. An engineer is designing a disinfection system that will rely on free chlorine as the disinfectant for Giardia. They have measured a chlorine breakpoint curve (below) to ensure the correct amount of free chlorine is generated. 0.90 (1) (1) (1) (4) W 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 Chlorine dose(mg/L) 0.80 0.70 0.60 0.50 0.40 0,30 0.20 0.10 0.00 Using the graph above (Chlorine dose (mg/L) vs. total chlorine residual (mg/L)), answer the following: a) What is the concentration of readily oxidizable substances? b) What is the breakpoint chlorination dosage? c) What is the dominant form of chlorine when the chlorine dose is 0.6 mg/L or less? d) The engineer must ensure that at least 3-log inactivation of Giardia occurs at 20C. The pH of the system varies between 7.0 and 8.0. The The time of this clearwell with average baffling is known to be 50 min. What should the measured total residual chlorine be at the exit of the clearwell to ensure 3-log disinfection under the conditions described? (reported as mg/L) (5) e) The engineer is worried that plans to first coagulate the water using alum (Al2(SO4)14H0; molecular weight= 600 g/mol) will change the design of the disinfection system. If the alkalinity of the water were measured to be 20 mg/l as CaCOs, would the addition of 65 mg/L of alum change the required CT? Indicate if the required CT will increase, decrease or stay the same? Why? Show your calculations, refer to the reactions below, and the CT tables attached to the exam. You can assume that all alkalinity is in the form of HCO and both reactions go to completion. Al (50), 14H0 + 6H0-2A1(OH)2)+6H*+350 +14H0 HCO5 + HCO + HO Page 3 of 5