Page 543 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

498 Fundamentals of Water Treatment Unit Processes: Physical, Chemical, and Biological

Required 15.6 Mass Balance as Design Principle (See Section
(a) Select two different adsorbates for your problem. 15.2.4.3)
(b) Pick a reasonable input concentration. Given
(c) Prepare a spreadsheet for your ‘‘solution’’ that is . HLR ¼ 6.1 m=h (2.5 gpm=ft ),
2
suitable for exploring various ‘‘scenarios.’’ . C 0 5.6 mmol=L,
(d) Pick two or more ‘‘scenarios’’ to explore using . Adsorbate 2,4-dichlorophenol,
your spreadsheet. . Adsorbent Columbia LCK, mesh 25 30,
(e) The spreadsheet should have as an ‘‘output’’ the . L(packed-bed) ¼ 10 m,
velocity of the wave front. Another output should . L wf 0.12 m,
be the length of the column required (depth of . v wf 0.50 m=day
carbon bed).
Required
(f) Your scenarios could be anything that relates to
(a) Calculate v wf by Equation 15.48 and compare with
design (e.g., different input adsorbate concen-
the value given in Figure 15.4.
trations, different HLRs, different times to
(b) Estimate t(breakthrough).
exhaustion, different column lengths, or different
temperatures). Solution
(g) Equation 15.48 is a means to determine the length (a) Formula for 2,4-dichlorophenol is C 6 H 4 OCl 2 ;MW
of the carbon bed. (2,4-dichlorophenol) ¼ 163.0 g=mol. Therefore [2,4-
dichlorophenol] ¼ 5.6 mmol=L 163 g=mol mol=1000
Hints
mmol 1000 mg=g ¼ 913 mg=L. From Table CD15.
. Most carbon beds in practice for water
A.1, the Freundlich coefficients for Filtrasorb 300t are
treatment vary in their length dimension from
K ¼ 157 and 1=n ¼ 0.15 (estimates since the GAC’s
about 3–4 m (e.g., at the Klein Water Treat-
are different). Now calculate v wf from Equation 15.48.
ment Facility) to perhaps 10 m (Denver Reuse
(b) Calculate t(breakthrough) from Equation 15.45.
Plant).
. The GAC may be any brand for which isotherm Discussion
data are available. Since the isotherm for 2,4-dichlorophenol and
. Your scenarios could be anything that relates Columbia LCK is not available readily, that for 2,4-
to design (e.g., different input adsorbate concen- dichlorophenol and Filtrasorb 300t, Table CD15.A.1
trations, different HLRs, different times to is used as a surrogate. This gives an approximation
exhaustion, different column lengths, or different for X*.
temperatures) 15.7 Rate of GAC Exhaustion (Love Canal Example)
. Equations 15.71, 15.72, and 15.73 provide a means
Given
to determine the length of the carbon bed.
Assume Filtrasorb 300t GAC is used for a packed-bed
15.5 Mass Balance as Design Principle
reactor to remove organics from water pumped from
Given Love Canal groundwater. Assume also that 2,4,6 tri-
2
HLR ¼ 10.2 m=h (4.2 gpm=ft ), adsorbate chloro- chlorophenol at concentration 84 mg=L, pH ¼ 6, is to
be removed (Table 15.10). Assume HLR 12.2 m=h
form in Louisville tap water, L(packed bed) ¼
2
(5.0 gpm=ft ) and ignore, for this problem, the issue of
10 m, 6 t(breakthrough) 12 weeks, 0.2
L wf 0.3 m, 0.0061 v wf 0.012 m=day. See competitive effects.
Section 15.2.4.20.
Required
Required Estimate the GAC exhaustion in terms of the velocity
Estimate a plausible influent concentration of chloro- of the wave front, i.e., v wf .
form in the tap water. 15.8 Effect of TCE Concentration on Run Time in GAC
Reactor (Section 15.2.3.1)
Solution
From Equation 15.48, estimate the ratio C 0 =X*(C 0 ). Given
Determine whether there is an unique point on the Let C(TCE) ¼ 20 mg=L in groundwater used as a
Freundlich isotherm for chloroform that satisfies the source for GAC treatment. GAC ¼ Filtrasorb 300t.
ratio calculated; if so, determine the associated values
Required
of C 0 and X*(C 0 ).
Determine the capacity of the GAC for TCE at
Discussion C(TCE) ¼ 20 mg=L, 5, mg=L, 40 mg=L, 100 mg=L.
The ‘‘back calculation’’ to determine C 0 and Plot the capacity in mg TCE=g GAC. Discuss the effect
X*(C 0 ) provides a means to corroborate empirical of higher concentrations of TCE on the capacity of the
data. GAC to adsorb TCE.