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a. Both liquid and cake sludges need to be stored. Suitable materials for
liquid-sludge storage tanks are typically carbon steel with a coating system compatible
with the sludge's chemical characteristics for smaller tanks, and concrete for very large
tanks. Tank equipment, such as mixers, should be constructed of corrosion-resistant
material, such as PVC, polyethylene (PE), or stainless steel. Construction materials for
sludge cake storage receptacles, such as hoppers, typically include carbon steel with a
coating system compatible with the sludge's characteristics. Refer to EM 1110-1-4008
for material compatibility.
b. Sludge conditioning equipment primarily includes a storage tank and mixer,
in addition to feed systems for the conditioning chemical. Materials of construction for
conditioning chemicals such as lime, ferric chloride, and polymers are discussed in
Subparagraph 2-18.104.22.168. Suitable materials for sludge conditioning tanks may include
FRP and coated steel.
c. Precoat equipment typically includes a precoat tank and mixer, pump, and
chemical feed system. Because of the abrasive nature of material used as precoat,
such as diatomaceous earth, suitable construction materials typical for the precoat tank
and chemical feed system are limited. A coating system that is compatible with the
sludge's characteristics and stainless steel are best, although plastic may be suitable to
a lesser extent. Suitable materials for the precoat pump are described in Subparagraph
d. Filter media wash systems typically used for filter presses include both
water and acid. No specific materials are required for the water wash system, although
polypropylene, polyethylene, and FRP are suitable. Because the acid wash system
typically involves the use of diluted hydrochloric acid, corrosion-resistant materials such
as FRP and rubber-lined steel are suitable for tanks, and PVC is suitable for piping.
2-22.214.171.124 Sludge Pumps and Piping. An overview of construction materials for pumps
used for sludge feed is presented in Subparagraph 2-4.3.2. Materials suitable for sludge
piping for filter presses typically include PVC, carbon steel, and stainless steel (WEF
1992). However, only carbon steel and stainless steel are recommended for operating
pressures greater than 690 kPa (100 psi).
2-8.1.3 Corrosion Protection. Corrosion protection is also an important design
consideration because of the frequent use of washing systems (water and acid) and
because of the use of corrosive conditioning chemicals, such as ferric chloride.
Therefore, the use of corrosion-resistant materials and coatings should be considered
for the press and supporting systems, such as the chemical handling systems used for
bulk storage, and feed and associated equipment, such as piping systems. Several
areas located within the filter press system may be subject to potential corrosion
problems. The primary concern is the area directly around the filter press because of
the use of high-pressure water to wash filter media. This may require that the area
around the press be constructed with corrosion-resistant materials, such as ceramic tile
for floor and wall coverings.