Wastewater Calculations - Mathematics and Statistics for the Environment - page 722

24.12.2 C onCentration F aCtor C alCulations
The concentration factor (CF) represents the increase in concentration resulting from the thickener;
it is a means of determining the effectiveness of the gravity thickening process:

Thickenedbiosolidsconcentration (%)
Inf

CF = (24.129)

luentbiosolids concentration (%)

■ EXAMPLE 24.98
Problem: The influent biosolids contain 3.5% solids. The thickened biosolids solids concentration
is 7.7%. What is the concentration factor?

Solution:

7.7%
3.5%

CF = = 2.2

24.12.3 a ir - to -s olids r atio C alCulations
The air-to-solids ratio is the ratio of the pounds of solids entering the thickener to the pounds of air
being applied:

3 3

Airflow (ft /min) × 0.0785 lb/ft

Air/solidsratio = (24.130)

Biosolidsflow(gpm)%Solids × × 8.34 l lb/gal

■ EXAMPLE 24.99
Problem: The biosolids pumped to the thickener are comprised of 0.85% solids. The airflow is 13
cfm. What is the air-to-solids ratio if the current biosolids flow rate entering the unit is 50 gpm?

Solution:

3 3

13 ft /min × 0.0785 lb/ft

Air/solidsratio = = 0.28

50 gpm × 0.0085 × 8.34 lb/gal

24.12.4 r eCyCle F loW in p erCent C alCulations
The amount of recycle flow can be expressed as a percent:

Recycleflowrate(gpm ×

flow (gpm)

100)

%Recycle = (24.131)

Sludge

■ EXAMPLE 24.100
Problem: The sludge flow to the thickener is 80 gpm. The recycle flow rate is 140 gpm. What is the
percent recycle?

Solution:

140 gpm 100
80 gpm

×

%Recycle = = 175%