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c. Dry polymers are typically available in powder, granular, microbead, and
flake forms. These polymers have high amounts of active solids, usually ranging from
90 to 95%. The shelf life is usually several years; however, cool, dry storage is required
because exposure to moisture tends to cake the polymer and make it unusable. Most
dry polymers are difficult to dissolve and require special equipment such as an eductor
or other prewetting device before they are delivered to the polymer solution mixing tank.
The solution should be mixed slowly, until the polymer is dissolved and then mixed or
aged according to manufacturers specifications because undissolved polymer can
cause clogging of pipes, pumps, and filter media. Once polymers are in the dilute form,
they are typically only usable and stable for 24 hours.
d. Liquid polymers are generally available in low to medium molecular weight,
with active solids ranging from 10 to 50%. Typical shelf lives range from 2 months to 1
year. This type of polymer should be protected from large temperature variations during
storage. When using higher viscosity liquid polymers, an adequate pump should be
used to transfer the polymer from the storage tanks to the mixing tanks. A wet dispersal
unit or static mixer should be used to disperse liquid polymers into the water.
e. The forms and characteristics of the polymers can greatly affect how they
react with sludge. Because characteristics differ from one sludge to another, the selec-
tion of the correct polymer requires treatability testing to determine the correct type as
well as the optimum chemical dosage. A description of treatability testing procedures
and requirements is presented in Paragraph 2-6.
f. Preconditioning handling facilities include polymer storage, preparation, and
feed systems. A detailed description of the polymer storage and preparation systems is
provided in Subparagraph 2-4.6.1.
g. Because polymer dosages are generally quite small, the concentrated
polymer needs to be diluted to be fed into the unit. Once the polymer is prepared, it is
typically introduced into the sludge feed stream through an in-line system that
continuously feeds the polymer to the press with the sludge, rather than as a batch. This
can be accomplished by either continuous pumping of sludge into a small tank and
addition of chemicals or by directly injecting the conditioning chemical into the sludge on
its way to the filter press. If the former method is used, deleterious effects may be noted
if storage and agitation are prolonged. A minimal retention time of 10 minutes at a
moderate degree of mixing (i.e., 75 rpm) is typically used (WEF 1992). A typical polymer
conditioning system is shown in Figure 2-6.
2-188.8.131.52 Filter Aids. In addition to ferric chloride and lime, other types of inorganic
materials have occasionally been used to condition sludge or act as a filter aid or filter
media precoat. The filter aid or body feed is added to slurries, particularly those con-
taining slimy or gelatinous solids, to provide structural integrity and porosity to the
sludge. This facilitates additional drainage when the sludge is compressed during the fil-
tration cycle. The use of filter media precoat is discussed in detail in Subparagraph 2-
4.6.2. Although using these materials may reduce the overall dosages of other