Solids Handling - Wastewater Operators - page 374

 Example 10.13

Problem: The influent sludge contains 3.5% solids. The thickened sludge
solids concentration is 7.7%. What is the concentration factor?

Solution:

7.7%
3.5%

ConcentrationFactor = = 2.2

10.5.4.5 Air-to-Solids Ratio

The air-to-solids ratio is the ratio between the pounds of air being
applied to the pounds of solids entering the thickener:

3 3

× 5lb/ft
Sludge Flow (gpm)%Solids8.34lb

AirFlow (ft /min)0.07

Air-to-SolidsRatio = (10.14)

× × /gal

 Example 10.14

Problem: The sludge pumped to the thickener is 0.85% solids. The air-
flow is 13 cfm. What is the air-to-solids ratio if the current sludge flow
rate entering the unit is 50 gpm?

Solution:

13 cfm0.075 lb/ft
50 gp

×
mm0.00858.34lb/gal

Air-to-SolidsRatio = = 0.28

× ×

10.5.4.6 Recycle Flow in Percent

The amount of recycle flow is expressed as a percent:

RecycleFlowRate(gpm) × 0 10

RecycleFlow(%) = (10.15)

Sludge Flow (gpm)

 Example 10.15

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

×

RecycleFlow = = 175%