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226 Fundamentals of Water Treatment Unit Processes: Physical, Chemical, and Biological
3. Second mixing tank. For the second mixing tank, 9.7 Conversion—moles=Ltomg=L
the detention time recommended is 10–30 min. Given=required
Let t (second tank) ¼ 30 min. Then,
The problems are stated as (a) and (b). The solutions
are straightforward and are freshman chemistry type con-
V(second tank) ¼ Q(first dilution) t(second tank)
versions (mentioned so that the problems are seen as not
¼ 0:080 L=s 1800 s
too involved). Example 9.3 illustrates the conversion
¼ 144 L procedure.
9.8 Metering Liquid Alum
From the Clarifloc A-210P data sheet, ‘‘polymer solution
Given=required
should be aged for 15–60 min for best results. Solution shelf
In treating the low turbidity in the water of a mountain
life is 8–16 h.’’ The 30 min detention time in the second
tank takes care of the aging requirement and consumes the stream (e.g., the Cache La Poudre River in Colorado)
polymer before the 8–16 h shelf life has occurred. the lowest effective alum concentration was determined
to be 26 mg Al 2 (SO 4 ) 3 14H 2 O=L (from a pilot plant
Discussion study). Assume the flow of raw water to the plant is
Since the tote tanks provide for continuous mixing of Q(raw water) ¼ 0.76 m =min (200 gpm), which is a
3
the emulsion and would involve less handling, tote tank
delivery would be preferred. To comply with the 6-month small plant.
shelf life, the delivery schedule should be about three tanks 9.9 Alum Manufacture
every 6 months. As a second point, the flow of diluted Given=required
polymer, Q(first dilution) ¼ 0.080 L=s, compares with Describe the manufacture of alum. Describe sources,
4
Q ¼ 1000 L=s, a factor of about 10 , compared with about manufacturing steps, annual production in the United
6
10 for the neat solution. Thus, the mixing requirement States, how it is packaged and delivered, the distribution
remains a major issue, but is less severe than if the neat infrastructure, and costs.
emulsion was used.
9.10 Historical Persons
Given=required
PROBLEMS Outline the contributions of A. P. Black to knowledge
of coagulation chemistry. W. F. Langlier. W Stumm,
9.1 Shulze-Hardy Rule
and former students.
Given=required 9.11 Alum in History
Describe the logic of the Shulze-Hardy rule.
Given=required
9.2 Theories of Coagulation
Outline coagulation practice in water treatment from
Given=required antiquity.
Coagulation theory has evolved to include such ideas as 9.12 Wastewater Coagulation
ion exchange, double layer, and sweep-floc. Describe
Given=required
briefly some of the key aspects of the evolution of the
What could be expected if coagulation is used as a unit
current theory.
process in treatment of raw wastewater in reduction of
9.3 Potential Barrier
BOD (or COD or TOC) and suspended solids? Verify
Given=required with laboratory jar tests.
Describe methods to reduce the magnitude of the poten- 9.13 Tertiary Wastewater Coagulation
tial barrier in the double layer theory.
Given=required
9.4 Bonding Energy between Particles—from DVLO
What could be expected if lime coagulation is used as a
Theory
unit process in treatment of secondary treated waste-
Given=required
water in reduction of BOD (or COD or TOC) and
Determine the order of magnitude of the bonding energy
suspended solids? Verify with laboratory jar tests. You
between two particles, expressed in kJ=mol. (1) Charge-
may wish to consider other coagulants, for example,
neutralization occurs and (2) DVLO theory applies.
ferric iron or alum.
Hint: Section 9.4.1.7 may serve as a starting point. 9.14 Selection of Coagulants
9.5 Equilibrium Constants—Aluminum
Given=required
Given=required How would you go about selection of coagulation
Generate the lines of the alum concentration versus pH chemicals for a new water treatment plant installation?
diagram by means of a spreadsheet. Outline important considerations.
9.6 Equilibrium Constants—Ferric Iron 9.15 Issues in Wastewater Coagulation
Given=required Given=required
Generate the lines of the ferric iron concentration versus Outline the issues for a program to determine if coagu-
pH diagram by means of a spreadsheet. lation should be used in treating a raw wastewater.