Pollution Prevention and Control Technologies for Plating
Section 6 - Wastewater Treatment
6.2 CONVENTIONAL TREATMENT TECHNOLOGIES
6.2.6 Sludge Dehydration
The solids content of the sludge dewatered on a filter press is
usually in the range of 25 to 60 percent. This represents an approximately
20 to 1 volume reduction from the original sludge volume discharged
from the clarifier/thickener. Additional dewatering can be accomplished
with sludge dehydration equipment that can produce a waste material
with a solids content of approximately 90%. This represents an
approximately 4 to 1 waste volume reduction above that achieved
by the filter press. Sludge dehydration equipment is available
in both batch and continuous operating modes. Batch units are
typically designed with a heated sludge chamber with rotating
blades that consistently break up and blend the sludge cake, thereby
exposing it to the heat source. Continuous units have a feed hopper
and employ an auger or conveyor system that moves a thin layer
of sludge through a drying region and discharges it into a hopper.
Some continuous units can be located such that the sludge cake
discharge from a filter press drops into the feed hopper of the
dehydration unit, making the overall dewatering process more automated.
System capacities range from less than 1 ft3/hr to more than 20
ft3/hr of feed. Various heat sources are used for sludge drying,
including: electric, electric infrared, steam and gas. Energy
requirements are mostly dependent on the water content of the
feed stock and the efficiency of a given unit. Sludge dehydration
equipment will require an air exhaust system.
During the past five years, sludge dehydration equipment has been
one of the most frequently purchased of all pollution prevention
and control devices. The Users Survey data show that 29 percent
of the plating shops have installed this technology and that approximately
80 percent of these units were purchased between 1988 and 1993.
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