UFC 3-280-03
23 JULY 2003
2-9.1.2.4 Poor Cake Release. Poor cake release can be caused by worn or improper
filter media, lack of precoating of filter media, or poorly conditioned sludge. The effects
of poor cake release result in increased cycle time, increased frequency of filter media
washing, and potential filter media damage.
a. There are several remedial measures that can reduce these effects. If the
filter media are worn, they should be replaced. If, however, poor cake release still
occurs, then a filter media of different construction material, permeability rating, or
surface finish may be required.
b. Poor cake release may also result from "too wet or sticky" sludge cake.
Use a precoat for this situation. Precoat systems are described in Subparagraph 2-
4.6.2.
c. Poorly conditioned sludge may also cause poor cake release. Sludge
conditioning should be optimized by doing tests, such as the CST or Buchner funnel
test, on the feed sludge and by making the proper chemical dosage adjustments.
2-9.1.2.5 Slow Filtration Rates. Many types of sludge (i.e., activated sludge) may
have slower filtration rates, longer cycle times, or lower solids content, even with
conditioning because of their inherent dewatering characteristics. However, if filtration
rates are slower than anticipated and a wet sludge cake is produced, filter media
blinding may be indicated. To alleviate this, wash the filter media.
2-9.1.2.6 Cloudy Filtrates. At the beginning of the filtration, the filtrate is typically
cloudy, unless a precoat or filter aid is used. However, if cloudiness persists, it may
mean that the system pressure is too high or fluctuating too much, that the filter media
are torn, or that the sludge is poorly conditioned. To remedy these conditions, a lower
pressure should be used, the filter media should be replaced, or the conditioning
requirement should be adjusted.
2-9.1.2.7 Determination of Dewatering Cycle Completion. Because the operator
cannot watch the sludge cake form, the end of the filter cycle is typically based on
experience from previous runs and, to some extent, on the elapsed cycle time when the
filtrate flow has been reduced to a minimum. Because operation of the press involves
the interrelationship of several process variables, the successful use of either timing
method requires experience with sludge characteristics, conditioning, and press
performance. During the dewatering process, these parameters should be monitored to
determine if adjustments to conditioning dosages or cycle times are required.
2-9.1.2.8 Lime Scaling. Using lime in the sludge conditioning process can cause
scaling in the sludge feed piping, on the filter media, and on the filter plates. If scale is
allowed to accumulate, the cycle time may be increased, throughput may be reduced,
cake release may be a problem, cake dryness may be reduced, and the filter media
may be blinded.
2-80
Previous Page
