Civil Engineering Reference
In-Depth Information
2
PA b
2
r
(23-9)
c
where:
r
specific resistance to filtration
P
pressure drop across sludge cake
A
surface area of filter
filtrate viscosity
c
weight of dry solids deposited per volume of filtration
b
slope of a plot of
t
/
V
versus
V
t
time of filtrate
V
filtrate volume
Specific resistance data can be used for comparing sludges and for evaluating the
effect of polymers on dewatering (see Fig. 23-4). Because the specific resistance of a
sludge often depends on the pressure applied during filtration (i.e., the compressibility)
and on the mixing applied during chemical addition, resistance values are used typi-
cally as an index of dewaterability rather than as well-defined sludge properties. Sludge
specific resistances change during storage as a result of chemical aging and biological
Optimum Conditioning
Chemical Dosage
0
1
2
3
4
5
Conditioning Chemical Dose, % by Weight
Fig. 23-4.
Use of specific resistance to determine optimum chemical dosage (
Source:
Refer-
ence 8; reprinted from
Handook of Practice: Water Treatment Plant Waste Management,
by
permission. Copyright
1987, American Water Works Association and AWWARF.)
