Environmental Engineering Reference
In-Depth Information
10.5.4.2 Surface Loading Rate
Surface loading rate (surface settling rate) is hydraulic loading—
the amount of sludge applied per square foot of gravity thickener:
Sludge Appliedtot
he Thickener(gpd)
ThickenerArea (ft )
2
=
Surf. Loading(gpd/ft )
(10.11)
2
Example 10.11
Problem:
The 70-ft-diameter gravity thickener receives 32,000 gpd of
sludge. What is the surface loading in gallons per day per square foot?
Solution:
32,000 gpd
0.785
= 8.32 gpd/ft
2
Surface Loading
=
×
70 ft
×
70 ft
10.5.4.3 Solids Loading Rate
The solids loading rate is the pounds of solids per day being applied
to 1 square foot of tank surface area. The calculation uses the surface
area of the bottom of the tank. It assumes that the floor of the tank is
flat and has the same dimensions as the surface:
⎡
% Sludge Sol
ids Sludge Flow (gpd)
8.34 lb/gal
×
⎤
⎢
⎥
×
(10.12)
Solids Loading Rate
(lb/day/ft)
⎣
⎦
=
2
Thi
ckener Area (ft )
Example 10.12
Problem:
The thickener influent contains 1.6% solids. The influent flow
rate is 39,000 gpd. The thickener is 50 ft in diameter and 10 ft deep.
What is the solids loading in pounds per day per square foot?
Solution:
0.016
×
39,000 gpd8.34l
×
b/gal
2.7lb/day/ft
2
Solids LoadingRate
=
=
0.78550ft50ft
×
×
10.5.4.4 Concentration Factor
The concentration factor (CF) represents the increase in concentra-
tion due to the thickener:
ThickenedSludge
Concentration(%)
Influent Sludge Concentration(%)
ConcentrationFactor (CF)
=
(10.13)
