CEE 350 - Korshin - Winter 2012 - Midterm(1)

# CEE 350 - Korshin - Winter 2012 - Midterm(1) - CLASS 350...

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CLASS 350 MIDTERM SOLUTIONS Problem 1 (0.4 point) A lagoon is to be designed to accommodate an input flow of 0.20 m 3 /s of a non-conservative pollutant with concentration 45.0 mg/L and reaction rate 0.25/day. The effluent from the lagoon must have pollutant concentration < 5.0 mg/L. Assuming complete mixing, how large must the lagoon be? The steady state calculations of the concentration can be done using the formula below: k Q V C C in ± 1 It follows therefore that for the known C in , C, Q and k, the volume is ¸ ¹ · ¨ © § ² 1 C C k Q V in The flow through the lagoon per day is 0.2(m 3 /s)·86400(s/day)=17280 m 3 /day. Therefore, we can obtain that ³ ´ ³´ 3 5 1 3 10 53 . 5 1 5 45 25 . 0 / 17280 1 m day day m C C k Q V in µ ¸ ¹ · ¨ © § ² ¸ ¹ · ¨ © § ² ² Problem 2 (0.4 point) Water carrying dissolved ozone travels along a 1200 meter long pipe. The linear velocity is 60 m/minute. The dissolved ozone decays exponentially in the water; the decay constant is 0.07 min -1 . Determine the concentration of ozone that must be present in the water entering the pipe to ensure that the ozone concentration in the water leaving the pipe is 0.2 mg/L. This can be calculated using the formula for exponential decay: ¸ ¹ · ¨ © § ² ² l U k C kt C C exp exp 0 0 Accordingly, the concentration that must be in the water entering the pipe can be determined as L mg l U k C C / 36 . 1 50 1200 08 . 0 exp 2 . 0 exp 0 ¸ ¹ · ¨ © § u u ¸ ¹ · ¨ © § Problem 3 (0.4 point) A river water used as a drinking water source has a bicarbonate (HCO 3 - ) concentration of 61 mg/L and a H 2 CO 3 concentration of 11 mg/L. What is the pH of this water? (Keep in mind that the first deprotonation constant of carbonic acid is 10 -6.3 ). The molar concentration of bicarbonate and hydrated CO 2 (wh ich is the same as mo lar concentration of H 2 CO 3 ) in the solution can be determined as shown below

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2 >@ ±² L mol M mg L mg MW C HCO HCO HCO / 10 / 000 , 61 / 61 4 3 3 3 ³ ³ ³ ³ L mol M mg L mg MW C CO H CO H CO H / 10 / 000 , 62 / 2 . 6 5 3 2 3 2 3 2 ³
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## This note was uploaded on 03/31/2012 for the course CEE 350 taught by Professor Korshin during the Spring '10 term at University of Washington.

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CEE 350 - Korshin - Winter 2012 - Midterm(1) - CLASS 350...

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