Water Treatment Processes - Mathematics and Statistics for the Environment - page 627

■ EXAMPLE 23.53
Problem: A circular clarifier receives a flow of 3.55 MGD. If the diameter of the weir is 90 ft, what
is the weir overflow rate in gpm/ft?

Solution:

3,550,000 gpd
1440 min/day

Flow = = 2465 gpm

Weir length = 3.14 × 90 ft = 283 ft

Flow (gpm)
Weirlength(f

2465 gpm
283 ft

Weir overflow rate = = = 8.7 gpm/ft

t)

23.5.6 p erCent s ettled b iosolids
The percent settled biosolids test ( volume over volume test , or V/V test) is conducted by collecting
a 100-mL slurry sample from the solids contact unit and allowing it to settle for 10 min. After 10
min, the volume of settled biosolids at the bottom of the 100-mL graduated cylinder is measured
and recorded. The equation used to calculate percent settled biosolids is shown below:

Settled biosolids volum ee(mL)

Totalsample volume(mL)

%Settledbiosolids = ×100 (23.54)

■ EXAMPLE 23.54
Problem: A 100-mL sample of slurry from a solids contact unit is placed in a graduated cylinder
and allowed to set for 10 min. The settled biosolids at the bottom of the graduated cylinder after 10
min is 22 mL. What is the percent of settled biosolids of the sample?

Solution:

Settled biosolids volum ee(mL)

Totalsample volume(mL)

%Settledbiosolids = × 100

22 mL
10

= ×= 100 19% settledbiosolids

00mL

■ EXAMPLE 23.55
Problem: A 100-mL sample of slurry from a solids contact unit is placed in a graduated cylinder.
After 10 min, a total of 21 mL of biosolids settled to the bottom of the cylinder. What is the percent
settled biosolids of the sample?

Solution :

Settled biosolids volum ee(mL)

Totalsample volume(mL)

%Settledbiosolids = × 100

21 mL
10

= ×= 100 21% settledbiosolids

00mL