Youâve been hired as a consultant by a pharmaceutical firm that produces naproxen. They have a production facility that discharges its wastewater into a municipal sewer. Your clientâs facility discharges 350,000 gallons per day at a temperature of 25°C. The city requires that 99% of the naproxen be destroyed in your clientâs effluent prior to discharge. You are asked to analyze and compare total costs of the pre-treatment system that use chlorine to achieve this goal. Consider only the cost of construction of a chlorine contact tank of the appropriate size and the cost of sodium hypochlorite that must be added. Look at 3 pHs (6, 7 and 8) and a range of chlorine concentrations (0.3 â 30mg/L). Here are the recommended steps.
a) Using the rate data you developed in the laboratory portion, estimate the 2nd order apparent rate constant (kapp) for pH 6.0 and 25°C. From this, calculate the time required for 99% removal in a PFR (recognizing that a PFR will be superior to a CMFR for this process) under these conditions (i.e., pH 6.0 and 25°C) presuming a chlorine residual of 30 mg/L. You should also presume that chlorine is always in great excess over Naproxen so you should still use a pseudo-first order equation. This means that you take the kapp you calculated and multiply it by your chlorine dose (in moles/L) to get the new pseudo-1st order âkâ for your design calculation (i.e., the k in C=Coe-kt).
b) Calculate the tank volume needed in cubic meters
c) Determine the 1978 construction cost
d) Update that cost to the 2010 construction cost
e) Determine the CRF and then the EAC assuming a 20 year payback period and a
5% annual interest rate
f) Calculate the annual usage rate of chlorine in kg/yr
g) Calculate the annual cost for that chlorine
h) Add this to the EAC to get the total annual project cost
i) Repeat steps âaâ through âhâ for a range of chlorine concentrations from 0.3-30
mg/L. It would be worthwhile to set up a spreadsheet to do this, so you can
determine many values along this range.
j) Plot total annual project cost (in $/yr) vs chlorine dose (in mg/L)
k) Repeat âaâ through âjâ for pH 7.0 and again for pH 8.0.
l) Comment on your calculations. Which design do you prefer? What else would
you want to take into consideration before adopting a target pH? Are there any other design or operating variables youâd like to consider?
Youâve been hired as a consultant by a pharmaceutical firm that produces naproxen. They have a production facility that discharges its wastewater into a municipal sewer. Your clientâs facility discharges 350,000 gallons per day at a temperature of 25°C. The city requires that 99% of the naproxen be destroyed in your clientâs effluent prior to discharge. You are asked to analyze and compare total costs of the pre-treatment system that use chlorine to achieve this goal. Consider only the cost of construction of a chlorine contact tank of the appropriate size and the cost of sodium hypochlorite that must be added. Look at 3 pHs (6, 7 and 8) and a range of chlorine concentrations (0.3 â 30mg/L). Here are the recommended steps.
a) Using the rate data you developed in the laboratory portion, estimate the 2nd order apparent rate constant (kapp) for pH 6.0 and 25°C. From this, calculate the time required for 99% removal in a PFR (recognizing that a PFR will be superior to a CMFR for this process) under these conditions (i.e., pH 6.0 and 25°C) presuming a chlorine residual of 30 mg/L. You should also presume that chlorine is always in great excess over Naproxen so you should still use a pseudo-first order equation. This means that you take the kapp you calculated and multiply it by your chlorine dose (in moles/L) to get the new pseudo-1st order âkâ for your design calculation (i.e., the k in C=Coe-kt).
b) Calculate the tank volume needed in cubic meters
c) Determine the 1978 construction cost
d) Update that cost to the 2010 construction cost
e) Determine the CRF and then the EAC assuming a 20 year payback period and a
5% annual interest rate
f) Calculate the annual usage rate of chlorine in kg/yr
g) Calculate the annual cost for that chlorine
h) Add this to the EAC to get the total annual project cost
i) Repeat steps âaâ through âhâ for a range of chlorine concentrations from 0.3-30
mg/L. It would be worthwhile to set up a spreadsheet to do this, so you can
determine many values along this range.
j) Plot total annual project cost (in $/yr) vs chlorine dose (in mg/L)
k) Repeat âaâ through âjâ for pH 7.0 and again for pH 8.0.
l) Comment on your calculations. Which design do you prefer? What else would
you want to take into consideration before adopting a target pH? Are there any other design or operating variables youâd like to consider?
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