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Sedimentation 129

6.10 Histograms for Removal 6.17 Application of Flux Theory to Design (6.7.1.2 Sludge
Thickening)
Given=Required
The tabular data of Tables 6.7 and 6.8 are for primary Given=Required
settling basins. Plot histograms of percent removal of a. From Figure 6.17a, obtain the associated plot
suspended solids for (a) rectangular basins and (b) cir- for the flux density, j(settling) versus X i ,asin
cular basins. Discuss your findings. Figure 6.17b.
6.11 Removals of Suspensions as Function of Independ- b. Assume data for underflow and estimate j(bulk).
3
ent Variables c. For Q ¼ 0.044 m =s (1.0 mgd), determine the area
Given=Required required for a secondary clarifier.
For the basins of Tables 6.7 and 6.8, plot percent 6.18 Application of Flux Theory to Secondary Clarifier
removal of suspended solids v. v o for (a) rectangular Operation
basins and (b) circular basins. Discuss your findings. Do Given=Required
thesameusing detentiontimeastheindependentvariable. For the final clarifier design of Example 6.6, explore
Try a three-dimensional plot that combines v o and u as the effect of modifying operating conditions. The
independent variables. spreadsheet, Table CD6.5 is recommended. Modifica-
6.12 Basin Design for Flocculent Settling tion may be useful. Some of the questions that may be
Given=Required explored include: (a) suppose the underflow solids
Design a rectangular sedimentation basin to remove concentration is say, X r ¼ 4000 mg=L, (b) X r ¼ 8000
70% of the suspension described in Figure 6.14 (and mg=L, (c) suppose the operator chooses to increase R,
with removals compiled in Figure 6.19 (Hendricks, and (d) suppose the future solids loading to the final
2006) reproduced below). clarifier is increased by say 30% (caused by increased
6.13 Basin Design for Flocculent Suspension organic loading to the reactor and consequent greater
production of bio-solids). Can the clarifier handle this
Given=Required
increased load? Will solids overflow? Describe in
For the suspension of Figure 6.14, select basin dimen- terms of theory.
3
sions for Q ¼ 0.044 m =s (1.0 mgd); let R ¼ 80%.
6.19 Application of Flux Theory to Performance
Extend the spreadsheet to Table 6.7 to include the
Evaluation
determination of w and L. Discuss your outcome for
v H and the basin proportions. Given=Required
6.14 Basin Performance for Flocculent Suspension if Q Suppose, in the Example of 6.6, a clarifier of diameter
3
Increases 12.2 m (40 ft) already existed. Let R ¼ 0.0219 m =s (0.5
mgd). Determine the effect on underflow concentration,
Given=Required
X r , and X. Describe the performance consequences of
Determine the performance of the basin in terms of R
this design.
and effect on scour if Q is increased by a factor of two.
6.20 Application of Flux Theory to Effect of Changing
6.15 Linking Activated-Sludge Reactor Variables to Sec-
Operating Variables
ondary Clarifier Performance (Requires Additional
Study) Given=Required
Suppose, in the Example of 6.6, a clarifier of diameter
Given=Required
12.2 m (40 ft) already existed. As an operating variable,
Based on the paper of Hermanowicz (1998) in which
R can be increased. Describe the scenario quantitatively
plots were developed for the relationship, X ¼ f(R=Q, X r ,
and descriptively. As a second consideration, evaluate
u, SOR, SVI), (a) develop the same thing by means of a
the effect on the reactor (detention time is the direct
spreadsheet, i.e., the output should be X as a function of
effect).
X r for given values of R=Q, u, and SVI, (b) duplicate the
graphical outputs as illustrated in Figure 7 of his paper. Hint: Consider the effect of R on j(bulk) and the asso-
Comment on the significance of this integration of vari- ciated materials balance.
ables. Note that SOR ¼ (Q W )=A(plan), Equation 6.21 Hindered Settling
6.23, and u ¼ (R þ W )=A(plan), Equation 6.24. Defin- Given
itions are X ¼ MLSS (mixed liquor suspended solids) A typical concentration of activated sludge solids
and R is calculated from assumed, X, X r . (mixed liquor suspended solids, MLSS) is about 2000
6.16 Application of the Vesilind Equation (6.6.1.2 Settling mg=L. After settling, the suspension concentration, X r ,is
Tests) about 10,000 mg=L.
Given=Required Required
Estimate v I and b for the plot of Figure 6.17a, which is Calculate the size for an ideal final settling basin for an
from the data of Dick (1970). Compare with the data of activated sludge suspension. Compare your size with a
Watts et al. (1996) in which v 1 ¼ 7.62 m=h and real basin. Use real data for flow to the basin from a
b ¼ 0.00024 L=mg ¼ 0.24=g (Table 6.4). nearby wastewater-treatment plant.