Environmental Engineering FOURTH EDITION

220 ENVIRONMENTAL ENGINEERING

Fixed Solids collect

head in frames Movable head

Material enters

Figure 10-10. Pressure filters. (Photo courtesy of Envirex.)

The factor b may be determined from a simple test with a Buchner funnel (Fig. 10-12).
The sludge is poured onto the filter, a vacuum is applied, and the volume of the filtrate
is recorded against time. The plot of these data yields a straight line with slope b.
Table 10-3 lists approximate ranges for specific resistance for different sludges.

EXAMPLE 10.4. Results of a Buchner funnel sludge filterability experiment are shown
below. Calculate the specific resistance to filtration. Note that the first 2 min are ignored,
partly because of storage of water in the filter and partly because the resistance of the
filter becomes negligible after this time allowance.