UFC 3-280-03
23 JULY 2003
press include: lower operating and maintenance requirements for sludge feed pumps
because the sludge can be pumped into the system at a much lower pressure; the
ability to dewater marginally conditioned sludge and sludge with variable or changing
characteristics to a high solids content; the use of polymers for conditioning versus lime
or other inorganic chemicals that may increase the sludge volume and disposal costs;
and precoats typically used to aid in the removal of sludge cake from the press are not
required. A more detailed description of the applicability and use of conditioning
chemicals and precoats is presented in Subparagraphs 2-4.4.5 and 2-4.6.2,
respectively.
2-3.2.2 Disadvantages. As shown in Table 2-2, plate and frame filter presses have
the following disadvantages compared with other sludge dewatering systems. The initial
cost for filter presses is high, and operation and maintenance costs are high if the
sludge is poorly conditioned and the filter press is not automatic. Filter cloth (water and
acid) washing is labor intensive, and replacement costs are high. Larger quantities of
conditioning chemicals are required and additional chemicals (precoat) may also be
required to release the cake from the filter. Batch discharge versus continuous dis-
charge after dewatering cycles may require additional facilities to receive and store the
sludge cake pending further disposal. In addition, the sludge feed may require grinding
and prescreening equipment, and the noise level would be very high because of the
feed pumps.
The disadvantages of the fixed-volume filter press versus the variable-volume
press are presented in Table 2-3. The primary disadvantage of the variable-volume
press system is that the initial cost of equipment can be as much as two to three times
that of the fixed-volume system. Another disadvantage is that, although the cycle time of
the variable-volume press system is lower than that of the fixed-volume system, the
volume of sludge generated per cycle of a similarly sized variable-volume press is gen-
erally less than the capacity of fixed-volume presses. The variable-volume press is also
more mechanically complex, with complex instrumentation, and thus, higher overall
maintenance.
2-3.3
Filter Press Performance Data. Filter press performance is typically meas-
ured as a function of the following parameters: solids content in the feed, required
chemical dosages for conditioning, cake solids content, total cycle time, solids capture,
solids yield, and filtrate volume (EPA 1982a). Although measured separately, these pa-
rameters are interrelated. For example, as the solids in the feed increase, the condi-
tioning chemical dosages, total cycle time, and filter yield usually change. Another
example of this interrelationship is that when the conditioning chemical dosage is
increased, the solids content, solids capture, and yield all increase, while the cycle time
usually decreases. However, if the sludge is over-conditioned, the sludge cake volume
may increase, thus, increasing disposal costs.
2-3.3.1 Factors Affecting Performance. Several factors can affect filter press
performance. They can typically be divided into two general categories: process factors
and equipment factors. Process factors are primarily related to the characteristics of the
sludge. Equipment factors can further affect the sludge filtration performance.
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