UFC 3-280-03
23 JULY 2003
2-9.1.2 Operations Concerns. Nonuniform sludge feed distribution, improper sludge
conditioning, poor cake release, inoperable safety curtains, inability to estimate the
completion of the filter cycle, and lime scaling are all common operational problems.
Although these problems may be interrelated with the equipment design, they can also
be caused by changes in operations.
2-9.1.2.1 Sludge Feed Distribution. Non-uniform feed distribution can cause a pres-
sure differential between plates that results in plate deflection, plate breakage, and ex-
cessive wear to the filter media and stay bosses. The primary causes of the non-uniform
feed distribution are sludge pump stallout, prefiltration of sludge at the feed end of the
press, cloth blinding, and poorly conditioned sludge.
a. The prefiltration problem typically occurs in presses with a large number of
plates (i.e., 80 or more) or when air is trapped in the press. The effects of prefiltration
include the formation of sludge cake in the initial chambers of the press or prefiltering
before all downstream chambers are filled. To remedy this problem, the press can either
be prefilled with water prior to starting the sludge filtering cycle and then rapidly filled
with sludge, or the sludge can be fed into both ends of the press simultaneously.
b. Blinding of the filter media is another major cause of unequal sludge
distribution. Remedial measures to eliminate media blinding include modifying the
sludge feed rate, changing to a different type of filter media, and optimizing the uni-
formity of the sludge feed by proper storage and blending. The release of liquid sludge
from the feed core during sludge cake discharge can also result in cloth blinding. This
problem may be remedied by using the core blowing option to remove this material prior
to cake discharge.
c. Poorly conditioned sludge may also cause non-uniform feed distribution.
Improper sludge conditioning and associated remedial measures are described below.
2-9.1.2.2 Leakage. During normal operation, there will typically be a small amount of
leakage between the filter plates. Generally, with continued solids buildup, the leakage
will be reduced. However, excessive leakage can occur because of low hydraulic pres-
sure, wrinkles or holes in the filter media, and filter cake buildup in surface joints.
Remedial measures to minimize or stop leakage are increasing the sludge
feed pressure, replacing the filter media, and cleaning or removing sludge cake buildup
from surface joints. In addition to these measures, plates with gasketed filter media can
be used.
2-9.1.2.3 Improper Sludge Conditioning. Several factors may cause improper sludge
conditioning, including under-dosing or overdosing with conditioning chemicals or
inadequate mixing. To remedy this, the conditioned sludge should be evaluated
frequently. Paragraph 2-6 describes in detail sludge conditioning tests.
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