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Coagulation 227
Describe the nature and extent of each of these phases Required
(i.e. what you would hope to learn). Enumerate ‘‘meas- Determine the following:
ures of effectiveness’’ relating to technical effectiveness 1. The volume of storage required for the polymer for a
of the coagulation process and cost criteria. As a note, it 60 day supply
is not likely, for most situations, that the chemical 2. The rate of feed to a first stage batch mixing unit
treatment would be used in lieu of biological treatment. 3. The volume and motor size for the first stage mixing
The problem is intended as an exercise in approaching a unit
new problem as may be found in practice. 4. The rate of pumping from the first stage mixing unit
9.16 Models in Coagulation to the raw water flow
Given=required 5. Recommend a particular metering pump
Discuss the role of models in understanding coagulation 6. The quality control set-up (i.e., a 1000 mL cylinder
(e.g., descriptive, empirical, mathematical). set up online) to verify the metering rate
9.17 Metering Solid Polymers 7. Aspects of handling that are relevant, for example,
For this kind of problem, the manufacturer’sspecifications labeling, materials for pipelines, storage vessels,
sheet should serve for reference to provide density of pumps, etc.
dry polymer, storage conditions and time, strength and 9.19 Mixing and Metering Liquid Polymers
viscosity of first-stage polymer solution in first stage mix- Given
ing, mixer (impeller type, size, mounting angle in basin, A liquid polymer is to be prepared for metering into a
3
motor power), strength of second stage storage,strength of raw water flow, Q ¼ 1.00 m =s (23 mgd), for a water
polymer feed solution, etc. In addition, the manufacturer treatment plant. The concentration of polymer required
may have package systems for mixing and feeding of the for treatment is 0.5 mg=L polymer. Assume that an
solid polymer, including pump type and sizing. alternative metering system is planned, which is to
Given blend the polymer with a dilution water prior to injec-
. A solid polymer is to be prepared for metering into a tion into the raw water.
raw water flow for a water treatment plant. Required
3
. Q(plant) ¼ 1.00 m =s (23 mgd). Design a system to feed the polymer from polymer
. The polymer is 90% active polymer. storage to the injection jets into the raw water. Assume
. The concentration of polymer required for treatment
the injection is to follow rapid-mix.
is 0.5 mg=L polymer mass as provided by the manu-
Solution
facturer (as distinguished from active polymer mass).
Example 9.9 addresses some of the issues of mixing
Required of an emulsion, but which pertains, by and large, to
Determine the following: any mixing problem. For a neat polymer solution, the
1. The volume of storage required for the polymer for a solution may be pumped directly from the storage
60 day supply tank and blended into a flow of dilution water; a static
2. The rate of solids feed to a first stage mixing unit mixer could be used. While there is no known rule for
3. The volume and motor size for the first stage mixing dilution, about 100=1, that is, dilution flow to neat
unit polymer flow, could be used. The next step is to get
4. The volume and motor size for the second stage the diluted polymer flow mixed into the raw water
mixing unit flow after the rapid-mix. This may be done within a
5. The rate of pumping from the second stage mixing pipe with flow in the turbulent flow regimeandbya
unit to the raw water flow diffuser, with four to eight jets directed upstream. The
6. Recommend a particular metering pump jets might be placed in a ring manifold or perhaps a
7. The quality control set-up (i.e., a 1000 mL cylinder cross manifold that covers the cross section of
set up on-line) to verify the metering rate the pipe.
8. Aspects of handling that are relevant, for example, 9.20 Handling Polymers
labeling, materials for pipelines, storage vessels,
Given
pumps, etc. (see AWWA Standards)
Two kinds of polymers are being considered for use in a
9.18 Metering Liquid Polymers
water treatment plant: (1) polyacrylamide, and (2)
Given
epi=DMA polyamine.
A liquid polymer is to be prepared for metering into a
3
raw water flow, Q ¼ 1.00 m =s (23 mgd), for a water Hint: The AWWA Standards are first sources of infor-
mation on such questions.
treatment plant. The concentration of polymer required
for treatment is 0.5 mg=L polymer mass as provided by Required
the manufacturer (as distinguished from active polymer For one of these polymers, specify considerations for
mass). handling, such as follows: