Page 445 - Civil Engineering Formulas

STORMWATER, WASTEWATER, AND ENVIRONMENTAL PROTECTION 371

The wet cake discharge (lb/h) is
dry cake rate, lb/h
Wet cake discharge (lb/h) (13.39)
cake % solids
3
The volume of wet cake, assuming a cake density of 60 lb/ft is
wet cake rate, lb/h
Volume of wet cake (ft /h) (13.40)
3
cake density, lb/ft 3
The percent reduction in sludge volume is then
sludge volume in sludge volume out
% Volume reduction (13.41)
sludge volume in
The centrifugal acceleration force (G), defined as multiples of gravity, is a
function of the rotational speed of the bowl and the distance of the particle from
the axis of rotation. In the centrifuge, the centrifugal force, G, is calculated as
follows:
2
(2
N) R
G (13.42)
32.2 ft/s 2
where N rotational speed of centrifuge (rev/s)
R bowl radius, ft (cm)
The polymer feed rate (lb/h) of dry polymer is
(polymer dosage, lb/ton)(dry sludge feed, lb/h)
Polymer feed rate (lb/h)
2000 lb/ton
(13.43)
Polymer feed rate (gal/h) is

polymer feed rate (lb/h)
Polymer feed rate (gal/h)
(8.34 lb/gal)(s.g.)(% polymer concentration)
(13.44)
where s.g. specific gravity of the polymer solution
% polymer concentration expressed as a decimal

DESIGN OF A TRICKLING FILTER
USING THE NRC EQUATIONS

Two possible process flow schematics for a two-stage trickling filter system are
shown in Fig. 13.5.