CE 311 Environmental Engineering I
Dr. Kauser Jahan
Fall 2012
Assignment # 4 Due Friday September 28, 2012 by 5PM
1. Name four applications of gas transfer in environmental engineering.
2. The following data was obtained for a gas transfer experiment conducted at 20oC to evaluate
the performance of a submerged turbine aerator.
Plot for Obtaining Gas Transfer Coefficient
y = -0.2331x + 1.9389
2.5
ln(C*-Ct)
2
1.5
1
0.5
0
0
1
2
3
4
Time (seconds)
a) Determine the value of the gas transfer coefficient in min-1 for the aerator.
b) Determine KLa in min-1 at 30oC. Assume  = 1.04. KLa (T) = KLa(20C)  T-20
c) If the value of C* is 9.0 mg/L, what was the initial dissolved oxygen (Co) in mg/L at the start
of the experiment?
3. A gas transfer experiment results in the following data
Time (minutes)
Dissolved Oxygen (mg/L)
0
2.2
5
4.2
10
5.0
15
5.5
The water temperature is 15oC. What is the value of the gas transfer rate KLa in sec1? Cs = 10.07 mg/L at 15oC. Please plot data to obtain Kla.
4. A batch reactor is used to remove organics from wastewater using microbes. The
concentration of organics is 250 mg/L. The removal reaction is first order and
the removal rate is 0.015 min-1.
a)
How long (in hours) will it take for the organics concentration to be reduced to 25
mg/L?
b) What is the organics concentration after 20 minutes?
5. A CMFR shown below is being used to treat a pollutant with an influent
concentration of 125 mg/L.
20 feet
Q = 10 GPM
15 feet
12 feet
a) What is the volume of the reactor in Gallons?
b) What is the detention time in minutes?
c) If the pollutant removal is first order and the rate is 0.675 min-1, what is the
pollutant concentration in mg/L leaving the reactor?
c) What is the % removal of the pollutant?
Bonus
Prove that for n identical (same V, Q, td) CMFR reactors placed in
series the general expression is
𝑪𝒏
𝟏
=
𝑪𝒐 (𝟏 + 𝒌𝒕𝒅 )𝒏