(4 points) A company is designing a solar-driven portable water disinfection sys
ID: 902034 • Letter: #
Question
(4 points) A company is designing a solar-driven portable water disinfection system to be used by the military. The system is simply an inlet, tube, a pump, a well-mixed chamber, and an outlet tube. Water is pumped continuously into the chamber where it is irradiated with UV light before exiting through the outlet tube into a collection chamber. The disinfection rate constant for the UV light is 7.80 s-1, and the bacterial count must be reduced by 99.9%. Because the army needs to fit the unit into a backpack, they require that the unit’s chamber be no larger than 2.00 L. How much water will the system be able to produce during 10 hours of sunlight?
Explanation / Answer
This is a first order reaction:
lnC = -kt +lnCo
t = ln(Co/C) / k
= ln(100/0.1) / 7.8s-1
= 6.91/7.8 = 0.88 s
t=0.88 s is the time (residence time) needed to complete the disinfection for a 2L chamber.
10 h = 36000 s
36000s / 0.88 s/treatment cycle = 40909 cycles
40909 cycles x 2L = 81818 L of disinfected water produced in 10 h.
I doubt that this results is plausible. Maybe the actual disinfection rate constant is much lower.
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