Environmental Engineering FOURTH EDITION

Sludge Treatment and Disposal 223

70

55

:I 50

I I II

b=573

Figure 10-13. Laboratory filtration data from Example 10.4.

the filter per unit filter surface area per unit time,

where

YF = filter yield (kg/m2-s),

P = filter pressure (N/m2),

w = feed solids concentration (kg/m3),

p = filtrate viscosity (N-s/m2),

r = specific resistance to filtration (mkg), and

t = time on the filter (s).

(10.5)

EXAMPLE 10.5. A sludge has a solids concentration of 4% and a specific resistance to
filtration of 1.86 x 1013 dkg. The pressure in a belt filter is expected to be 800 N/m2
and the filtration time is 30 s. Estimate the belt area required for a sludge flow rate of
0.3 m3/s:

= 1.07 x 10-4kg/m2. s.

2(8m40)

yF = [ (0.01)(1.86 x 1013)(30)

This filter yield is approximately 8 lb/ft2-h, which is excellent production for a
dewatering operation.

The Biichner funnel test for specific resistance is rather clumsy and time consum-
ing. An indirect method for estimating how well sludge will filter uses the capillary
suction time (CST) apparatus, developed in Great Britain. The CST device, illustrated
in Fig. 10-14, allows the water to seep out of sludge (in effect, a liltration process)