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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:
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