Page 644 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Gas Transfer 599

18.4.2.3 Wurtsmith AFB: Oscoda, Miami dioxide concentration (by titration). From what
The contamination at the site was trichloroethylene (TCE), you know of Henry’s law, estimate the concen-
caused by a leaking underground storage tank near a main- tration that you would measure assuming no
tenance facility. Two packed-tower air strippers in series were experimental error of analysis.
installed, each 1.52 m (5 ft) diameter, 9.14 m (30 ft) high, with (c) Assume that you obtain a measurement of carbon
5.49 m (18 ft) 16 mm pall-ring packing, with air=water dioxide in (b) by titration. Describe the major
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ratio ¼ 25:1 and Q(water) ¼ 0.0378 m =s (600 gpm). The experimental error.
TCE removal was 0.86–0.98 fraction for a single tower and 18.4 Gas Transfer Coefficient—Is Determination for Oxygen
0.999 fraction overall. Biological growths were a maintenance Applicable to Different Gases Using the Same System?
problem and required repeated removal and cleaning. Given=Required
For a lab experiment, K L a was determined to be 0.029
min 1 for stripping or adding oxygen. Assume the
18.4.2.4 Hyde Park Superfund Site, New York
reactor was ‘‘complete mix.’’
The site treated Q ¼ 3.50 L=s (80,000 gpd) landfill leachate.
(a) Estimate K L a(benzene)
Total organic carbon (TOC) (influent) ¼ 4000 mg=L; the air
(b) Suppose, using the same reactor in the batch mode,
stripper removed about 0.90 fraction TOC.
you had to strip benzene at a concentration of
20 mg=L to a concentration of 0.5 mg=L. Estimate
the time required.
PROBLEMS
(c) Suppose the same reactor is used as a continuous-
18.1 Applications of Henry’s Law flow reactor, with flow coming in at the top and out
Given=Required at the bottom. Does this affect K L a? What should be
Determine the concentration of atmospheric gases the detention time?
(O 2 ,N 2 ,CO 2 ) using Henry’s law, Table H.5. 18.5 Application of W(O 2 ) versus rpm(Impeller) Character-
(a) At sea level at 258C. istic Curve for a System
(b) At the Engineering Research Center (ERC) at Given
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Colorado State University (CSU) elevation, eleva- . Assume Q ¼ 9000 m =d (375 m =h) (or 2.4 mgd).
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tion is 1615 m (5300 ft) at 258C based upon tabular . [BOD in BOD out ] ¼ 200 mg=L (0.200 kg=m ).
data or formula for the effect of elevation on atmos- . Assume also that the detention time for the reactor is
pheric pressure. u ¼ 6h.
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(c) Read the barometric pressure from the mercury . V(reactor) ¼ (375 m =h) 6h ¼ 2350 m .
barometer. Compare the reading with the estimate . A single 2.13 m (7.0 ft) impeller is used.
in (b). . A characteristic curve is given by Figure 18.15.
(d) Determine the concentration of the three atmos- . Elevation ¼ 1610 m
pheric gases in equilibrium with the atmosphere in . T ¼ 158C.
distilled water based upon observed barometric . A direct current motor is used.
pressure (or elevation of site). . Power expended is proportional to the rotational
18.2 Application of Henry’s Law to Oxygen velocity with 60 kW expended at 60 rpm.
Given=Required Required
Determine the concentration of oxygen using Henry’s (a) Determine the K L a required.
law: (b) Calculate rpm(impeller) for the system to provide
(a) At sea level at 258C. the required K L a.
(b) At the ERC elevation, elevation is 1615 m (5300 ft) Hint: Example 18.4 provides a pattern for solution. Note
at 258C based upon tabular data for the effect of that C s will reflect the elevation and temperature, which
elevation on atmospheric pressure, Table B.6, and in turn will affect K L a.
using Henry’s law coefficients, Table H.5. 18.6 Explanations of Test Results and Gas Transfer
18.3 Application of Henry’s Law to Carbon Dioxide Variables
Given=Required Given=Required
(a) Determine the concentration of carbon dioxide in (a) Measurements of dissolved oxygen levels in full-
equilibrium with the atmosphere in distilled water scale aeration tests, at various sampling points, often
at your location. show dissolved oxygen concentrations greater than
(b) Bubbles are seen emerging from a primary clari- saturation with respect to the atmosphere. Explain.
fier. The bubbles are determined to be about (b) Delineate in a mathematical format, the system
two-thirds carbon dioxide and one-third methane. variables which may influence K L a.
Assume that you have a Kemmerer water bottle (c) What important principles must be operative in
(device to take a water sample at some depth) and surface aerator performance with respect to turbu-
you bring up the sample to measure the carbon lence (i.e., scale of eddies, intensity of turbulence).