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the filter dewatering process for sub-cycles, such as filter media precoating, or returned
to the headworks of the treatment process with the remaining filtrate.
5-220.127.116.11 Compute Volume of Filtrate.
Filtrate volume = 53,000 L/d [(3.1 m3/d) x (1000 L/m3)]= 49,900 L/d
Water in lime solution = 1060 L/d
Water in ferric chloride solution = 530 L/d
Total of return flow = 51,490 L/d ~ 51,500 L/d (13,600 gpd)
(Note that in addition to the items listed above, the addition of process water used in the
dewatering system, such as water needed for filter media washing, will need to be con-
sidered. However, these quantities are specific to the dewatering equipment selected
and are not included for this example.)
5-18.104.22.168 Compute Total Solids in the Return Flow.
Total solids in conditioned sludge
Total solids in sludge cake
Difference total solids in return flow
30 kg/d (~70 lb/d)
Therefore, the sump for this example should be sized to store 51,500 L or 51.5 m3
(13,600 gallons) based on 1 day of storage.
5-2.3.6 Design Details. A diagram of the design of the filter press assembly is
presented in Figure 5-1.
DESIGN EXAMPLE NUMBER 2. This paragraph provides a design example
and supporting calculations for sizing a sludge-dewatering system.
Assumptions. The following assumptions and criteria are used for the design
of the sludge-dewatering system:
The characteristics of the sludge stream are given below:
Assumed type of sludge:
Design daily liquid sludge flow =
80,000 L/day (21,100 gpd)
Concentration of solids
Specific gravity of feed
The minimum dry solids allowed in the sludge cake will be 25 % by weight.