Wastewater Calculations - Mathematics and Statistics for the Environment - page 749

■ EXAMPLE 24.147
Problem: A 2000-mL sample of activated biosolids is tested for settleability. If the settled solids are
measured as 410 mL, what is the percent settled solids?

Solution:

410 mL
2000 mL

%Settleable solids = × 100 = 20.5%

24.15.6 s ettleable s olids C alCulations
The settleable solids test is an easy, quantitative method to measure sediment found in wastewater.
An Imhoff cone (plastic or glass 1-L cone; see Figure 24.12) is filled with 1 L of sample wastewater,
stirred, and allowed to settle for 60 min. The settleable solids test, unlike the settleability test, is
conducted on samples from the sedimentation tank or clarifier influent and effluent to determine
percent removal of settleable solids. The percent settleable solids is determined by

removed(mL/L)
Settledsolidsininfluent(mL/L)

Settled solids

%Settleable solids removed = ×100 (24.180)

■ EXAMPLE 24.148
Problem: Calculate the percent removal of settleable solids if the settleable solids of the sedimenta-
tion tank influent is 15 mL/L and the settleable solids of the effluent is 0.4 mL/L.

Solution: First determine removed settleable solids:

15.0 mL/L - 0.4 mL/L = 14.6 mL/L

Next, insert the parameters into Equation 24.180:

14.6 mL/L
15.0 m

%Settleable solids removed = ×= 100 97%

L/L

Imho Cone

Settled Solids, mL

FIGURE 24.12 One-liter Imhoff cone.