Water/Wastewater Laboratory Calculations - Basic Mathematics for Water and Wastewater Operators - page 241

■ Example 16.15
Problem: Calculate the percent removal of settleable solids if the settleable solids of
the sedimentation tank influent is 15 mL/L and the settleable solids of the effluent
is 0.4 mL/L.

Solution: First determine the settleable solids removed:

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

Next, insert the parameters into Equation 16.13:

removed(mL/L)
Settledsolidsininfluent(mL/L)
14.6 mL/L
15.0 mL/L

Settled solids

%Settleable solids removed = × 100

= × 100 = 97%

■ Example 16.16
Problem: Calculate the percent removal of settleable solids if the settleable solids of
the sedimentation tank influent are 13 mL/L and the settleable solids of the effluent
are 0.5 mL/L.

Solution: First determine removed settleable solids:

13 mL/L - 0.5 mL/L = 12.5 mL/L

Next, insert the parameters into Equation 16.13:

removed(mL/L)
Settledsolidsininfluent(mL/L)
12.5 mL/L
13.0 mL/L

Settled solids

%Settleable solids removed = × 100

= × 100 = 96%

TOTAL SOLIDS, FIXED SOLIDS, AND VOLATILE SOLIDS
Wastewater consists of both water and solids. The total solids may be further classi-
fied as either volatile solids (organics) or ixed solids (inorganics) (see Figure 16.3).
Normally, total solids and volatile solids are expressed as percents, whereas sus-
pended solids are generally expressed as mg/L. To calculate either percents or mg/L
concentrations, certain concepts must be understood:

• Total solids —The residue left in the vessel after evaporation of liquid from

a sample and subsequent drying in an oven at 103 to 105°C

• Fixed solids —The residue left in the vessel after a sample is ignited (heated

to dryness at 550°C)

• Volatile solids —The weight loss after a sample is ignited (heated to dryness

at 550°C)