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Unformatted text preview: .50/Z45’L ENVE 331, Winter 2009 Homework #2
Due on February 4th 2009 Mass Balance Problems: Problem 1:
Alcohol containing 15% salt is fed at a rate of 10 kga’min in a mixer (CSTR) that initially holds 100 L of 5% salt in alcohol. The exit solution leaves the mixer at a rate of IO kglmin. Determine the exit
concentration after 30 minutes in ppm and assume complete mixing. The density ofalcohol is 0.8 ngL and can be aSSumed constant due to low salt concentration. I 5' 'r’
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“2 ' m “2 52.5; f Well Problem 2; A CSTR is running at steady state with a flowrate of 50 mLfmin. At any instant of time you started
injecting a dye (2 mUmin with a dye concentration of 100 g/L} in the inlet line and continued to do so.
The inlet flow rate turned to (50+2} 52ml/min and the volume of the CSTR is 2500 ml. No reaction occurs
in the reactor. Find the concentration of the dye after 15 and 30 minutes. Be ore? z/ Ma»; 714mg? ﬂ/Jﬂmn— w I
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9671 (78 5‘2xocte38——Q_14_é£ 6e: 5; Problem 3: A lake With a surface area of 1.13 mil. is fed by a river with a flow rate of 5000 cfs. The ﬂow
rate in the river exiting the lake is 6000 ct‘s. A wastewater treatment plant discharges into the lake at the
rate of 1000 cfs. The concentration ofa non~ conscwative pollutant. A. in the plant effluent is 45.0 mg.«"L.
The concentration of A in the Inﬂuent river is 1.1 ntg’L. [t'the pollutant A gets biodegraded with a ﬁrst
order rate of l .6lyear, what is the concentration of A in the lake at steady state? 4 /;../g;:. a; 5%; i Problem 4: You have a backyard Kot pond of 400 L. Due to its age, a good amount of solid deposited and you want to
ﬂush ofthe solids using fresh clean water. If the initial soild concentration is 60 mgx’L. and you need to
decrease the concentration to less than S ngI in 60 minutes. What ﬂow rate of fresh water do you need? Consider the the pond to behave as an CMF, Problem 5: Josh, .hm, Joe and John live in a room that is 15 x 15 x 4 meters in dimension. Joe and John
smoke ten Cigarettesfday each. Each Cigarette produces 0.9 pg of toxic chemical Benzene.
Benzene is degraded in air with ﬁrst order rate constant of 0.030/day. lfa fresh air flow rate of
20 m3fmin is maintained. what will be the BAP concentration after 2 hours. Consider the initial
concentration of benzene before the air [low started was 20 rig/ml (15) ...
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 Winter '08
 VIGIL
 Environmental Engineering

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