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bags are emptied, the storage and polymer mixing area should be well ventilated, and
proper eye protection and respirator equipment should be available.
(1) The dry polymer preparation and feed equipment typically consists of a
dry feed or an eductor or dispenser, mixing tank and mixer, feed tank, and supporting
solution and chemical feed metering pumps. The solution preparation system can be
either manual or automatic.
(2) The dry polymer is dispensed into the solution preparation system by hand
or volumetric feeder (i.e., screw or vibrating-type) to an eductor. The eductor is used to
prewet the dry polymer before adding it to the water in the solution mixing tank. The
working solution is then mixed and aged from 30 minutes to 2 hours. A variable-speed
mixer, with a maximum speed not to exceed 500 rpm, should be used. The aged
polymer is then pumped or transported to a polymer solution feed tank (day tank). This
tank should be adequately sized to hold a 24-hour supply of polymer. From the day
tank, the polymer is then dispensed into the sludge stream by metering pumps. The
metering pumps should be positive displacement pumps that have a variable-speed
controller that can be adjusted to the sludge flow. In general, diaphragm-type pumps are
used for applications of 6.3 L/s (100 gpm) and lower; and progressive cavity, gear, or
lobe pumps are used for applications greater than 6.3 L/s (100 gpm). In most
applications, the polymer is further diluted with water and is either injected into the
sludge through an in-line entry point or added and mixed in a sludge conditioning tank.
If dilution water is used, the dilution system should be equipped with a flow meter, such
as a rotameter, and control valves for flow adjustment. The tanks, piping, and valves for
this type of polymer system are typically constructed of PVC and fiberglass. Any metal
that may come in contact with the polymer solution should be stainless steel.
b. Liquid Polymer Feed Systems. Liquid polymers are typically available in
20-L (5 gallon) pails, 210-L (55-gallon) drums, 950-L (250-gallon) bins, or by bulk in
18.9-kL (5000 gallon) tank trucks. Liquid polymer should be stored in heated areas
equipped with adequate ventilation because it can generate harmful fumes and
unpleasant odors. The shelf life of liquid polymers is typically from 2 months to 1 year.
Tanks used for bulk storage are typically steel tanks lined with a polymer-resistant
coating or fiberglass tanks with a storage capacity of 150% of tank truck capacity or 15
to 30 days' anticipated use. Refer to EM 1110-1-4008 for material compatibility charts.
Depending on the quantity of liquid polymer required and the form of delivery
used, liquid feed systems range from large polymer solution preparation systems to
compact blending systems. The only difference between large polymer systems and dry
polymer systems is that the dry polymer working solution doesn't have to be prepared.
Liquid polymer solutions are prepared by manually or automatically dispensing the liquid
polymer and water into a tank. The dosage of liquid polymer into the tank is controlled
with a variable-speed metering pump. From the tank, the liquid polymer solution is
dispensed along with the sludge feed stream into a conditioning mixing tank or directly
injected and further diluted by water prior to in-line mixing with the sludge feed stream.
In addition to using the liquid polymer system as a stand-alone conditioning process,
this type of system can also be combined with the dry polymer feed system.