23 JULY 2003
2-126.96.36.199 Cake Breakers. Cake breakers are an essential design option that break the
sludge into smaller particles for further treatment and disposal. The design of the cake
breakers is based on the structural properties of the dewatered cake and desired
particle size. Typically, cake breakers consist of wires, bars, or cables located beneath
the filter. The cake breakers are typically aligned parallel to the length of the press and
spaced at a distance of 300 to 600 mm (12 to 24 inches) apart.
Filter Press Accessories and Auxiliary Systems. Accessories and auxiliary
systems used to support the filter press include the following: filter press feed (sludge
transport) and prefilling, chemical conditioning, filter media precoating, filter cloth (water
and acid) washing, filtrate and sludge cake handling, and supplying compressed air.
Detailed descriptions of the types of pumps required for liquid sludge transport and
filtrate and sludge cake handling are presented in Paragraphs 2-4.3 and 2-4.8 through
2-4.10, respectively. Therefore, the information presented in this paragraph will only
describe chemical feed, precoatings, filter media wash, and compressed air systems.
2-4.6.1 Chemical Feed Systems. Chemical feed systems for filter presses typically
consist of conditioning, precoating, and acid wash systems. Chemical feed systems for
the precoating and the acid wash systems will be described in detail in Subparagraphs
2-4.6.2 and 2-4.6.3, respectively.
The following subparagraphs present an overview of the conditioning chemical
feed systems for lime, ferric chloride, or polymer preparation, and chemical feed control
systems. Guidelines selecting and using specific conditioning chemicals are presented
in detail in Subparagraph 2-4.4.5. Detailed descriptions of these conditioning chemical
feed systems are presented in EPA (1987), WPCF (1983), and WEF (1992).
2-188.8.131.52 Lime Feed Systems. Lime handling equipment typically used for filter
presses use either a quick lime (CaO) or hydrated lime Ca(OH)2. Both forms are
typically available in 36- and 45-kg (80- and 100-pound) multiwalled paper bags and in
bulk. Quick lime in bulk is typically used for large presses (i.e., greater than 114 kg/hr
[250 lb/hr] or 900 to 1800 kg/day [1 to 2 tons per day]) because it is more economical to
use than hydrated lime.
a. Quick lime (CaO) is commonly available in three grades: 88 to 96% CaO,
75 to 88% CaO, and 50 to 75% CaO. To use quick lime, a calcium hydroxide slurry
must be prepared using water. This process, called slaking, generates heat and, thus,
special equipment is required. In general, only quick lime that is highly reactive and
quick slaking should be used for conditioning. A slurry ranging up to 25% by weight can
be prepared by slaking, although a maximum of 10% or less is typical. Special
consideration must also be given to storing the quick lime in a dry area because even
moisture in the air may cause it to react and become unusable.
b. Hydrated lime is much easier to handle than quick lime because it does not
require slaking, it can be easily mixed with water (without generation of excess heat),