Environmental engineers and scientists are concerned about pharmaceuticals (such as antibiotics) in the manufacture of Teflon) in the environment. A well-mixed lake is fed by two rivers. The flows and antibiotic concentrations are, respectively, 1.2 m3 /s and 0.30 mg/L in River A and 1.4 m3 /s and 0.25 mg/L in River B. The lake has a constant volume of 18,000 m3 and is drained by a river with a flow of 2.6 m3 /s. The antibiotic is degraded naturally in the lake with a first-order rate constant of 1.4 hr–
Problem 1: Environmental engineers and scientists are concerned about pharmaceuticals (such as antibiotics) in
the manufacture of Teflon) in the environment. A well-mixed lake is fed by two rivers. The flows and antibiotic
concentrations are, respectively, 1.2 m3
/s and 0.30 mg/L in River A and 1.4 m3
/s and 0.25 mg/L in River B. The
lake has a constant volume of 18,000 m3
and is drained by a river with a flow of 2.6 m3
/s. The antibiotic is degraded naturally in the lake with a first-order rate constant of 1.4 hr–1
.
A. Draw a sketch of the system. Indicate the control volume by a dashed line. What kind of hydrodynamic
model should you use for the lake in this problem? What mixing conditions should you assume?
B. Write the mass balance equation in words. Do not assume steady-state conditions yet.
C. Write the mass balance equation for the antibiotic in symbols. Do not assume steady-state conditions yet. For
full credit, define your symbols.
D. What is the antibiotic concentration in the river draining the lake (at the lake exit point) at steady state?
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