CIVIL ENGINEERING FORMULAS

STORMWATER, WASTEWATER, AND ENVIRONMENTAL PROTECTION 371

The wet cake discharge (lb/h) is

(13.39)

The volume of wet cake, assuming a cake density of 60 lb/ft^3 is

(13.40)

The percent reduction in sludge volume is then

(13.41)

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:

(13.42)

whereNrotational speed of centrifuge (rev/s)
Rbowl radius, ft (cm)

The polymer feed rate (lb/h) of dry polymer is

(13.43)

Polymer feed rate (gal/h) is

(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.

Polymer feed rate (gal/h)

polymer feed rate (lb/h)

(8.34 lb/gal)(s.g.)(% polymer concentration)

Polymer feed rate (lb/h)

(polymer dosage, lb/ton)(dry sludge feed, lb/h)

2000 lb/ton

G

(2 N)^2 R

32.2 ft/s^2

% Volume reduction

sludge volume insludge volume out

sludge volume in

Volume of wet cake (ft^3 /h)

wet cake rate, lb/h

cake density, lb/ft^3

Wet cake discharge (lb/h)

dry cake rate, lb/h

cake % solids