TM 5-814-3/AFM 88-11, Volume III
(2) Process description. Good chemical conditioning is very important for successful and consistent
performance of the belt filter press. A flocculant (usually an organic polymer) is added to the sludge prior
to its being fed to the belt press. Free water drains from the conditioned sludge in the gravity drainage stage
of the press. The sludge then enters a two-belt contact zone where a second, upper belt is gently set on the
forming sludge cake. The belts, with the captured cake between them, pass through rollers of generally
decreasing diameter. This stage subjects the sludge to continuously increasing pressures and shear forces.
Pressure can vary widely by design, with the sludge in most presses moving from a low pressure section to
a medium pressure section. Some presses include a high pressure section which provides additional
dewatering Progressively more and more water is expelled throughout the roller section to the end where the
cake is discharged. A scraper blade is often employed for each belt at the discharge point to remove cake
from the belts. Two spray-wash belt cleaning stations are generally provided to keep the belts clean.
Typically, secondary effluent can be used as the water source for the spray-wash. High pressure jets can be
equipped with a self-cleaning device used to continuously remove any solids which may tend to plug the spray
nozzles.
(3) Performance variables. Belt press performance is measured by the percent solids of the sludge cake,
the percent solids capture, the solids and hydraulic loading rates, and the required polymer dosage. Several
machine variables including belt speed, belt tension and belt type influence belt press performance.
(4) Advantages and disadvantages. Table 16-4 lists some of the advantages and disadvantages of the
belt filter press compared to other dewatering processes.
16-6
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