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considerations and guidelines that can be used to optimize coagulation and flocculation
conditions (WEF 1992):
Provide variable-speed mixers in the conditioning tank or in-line mixing to
minimize floc shearing of conditioned sludge.
Use diluted chemical solution to improve mixing with the sludge.
Provide individual conditioning for each type of sludge to maintain constant
chemical feed rate and concentration.
Locate the point of chemical conditioning as close to each dewatering unit as
Make sludge as homogeneous as possible to minimize the need for individual
adjustment of polymer for multiple thickening or dewatering units.
d. Sludge conditioning for plate and frame filter presses generally requires the
system to add lime and ferric chloride, lime only, or polymer, or ash or other granular
material to the sludge, before filtering, to produce a low-moisture sludge cake. Lime and
ferric chloride have been the conventional chemicals used for conditioning, especially
for fixed-volume press systems. However, polymers have become more frequently used
for the variable-volume press systems because of the decrease in sludge volume
generated, reduced chemical costs, and reduced ammonia odors. Typically, biological-
type sludge (i.e., municipal sludge) is chemically conditioned using ferric chloride and
lime or lime alone, whereas chemical-type sludge (i.e., metal hydroxides) is chemically
conditioned with either lime or polymers. The advantages of using polymers over
inorganic conditioning chemicals include (EPA 1987):
Polymers produce little additional sludge volume that would need to be dis-
posed of. Inorganic chemicals may increase the sludge volume by 15 to 30%.
If the dewatered sludge is going to be incinerated, polymers do not lower the
Polymers are easier and safer to handle than inorganic chemicals.
Polymers result in easier operation and maintenance than inorganic chemi-
cals that require frequent cleaning of equipment (e.g., acid baths).
e. Therefore, because reducing and minimizing volume is the primary goal of
processing and disposal of sludge, as well as providing low disposal costs, polymers
should be used if technically and economically feasible, especially for HTRW
f. Specific sludge applications and typical types and dosages of conditioning
chemicals used for both fixed-volume and variable-volume filter presses are summa-
rized in Tables 2-4 and 2-5, respectively. Unless treatability studies have been per-
formed and specific polymer dosages have been obtained, the preliminary design may
be best developed on the basis of the use of anticipated design dosages of conditioning
chemicals, such as ferric chloride or lime listed in these tables.
2-22.214.171.124 Lime and Ferric Chloride Conditioning. Inorganic conditioning usually
uses chemicals, such as lime and ferric chloride, although other metal salts, such as