Wastewater Calculations - Mathematics and Statistics for the Environment - page 748

No.ofequivalentsofsolute
L

Normality () N = (24.178)

iters of solution

■ EXAMPLE 24.144
Problem: If 2.0 equivalents of a chemical are dissolved in 1.5 L of solution, what is the normality
of the solution?

Solution:

No.ofequivalentsofsolute
L

2.0 equivalents
1.5 L

Normality () N = = = 3 N 1.3

iters of solution

■ EXAMPLE 24.145
Problem: A 800-mL solution contains 1.6 equivalents of a chemical. What is the normality of the
solution?

Solution: First convert 800 mL to liters:

800 mL ÷ 1000 mL = 0.8 L

Then calculate the normality of the solution:

1.6 equivalents
0.8 L

Normality = = N 2

24.15.5 s ettleability (a Ctivated b iosolids s olids ) C alCulations
The settleability test is a test of the quality of the activated biosolids solids—or activated sludge
solids (mixed liquor suspended solids). Settled biosolids volume (SBV)—or settled sludge volume
(SSV)—is determined at specified times during sample testing. For control, 30- and 60-minute
observations are made. Subscripts (SBV 30 or SSV 30 and SBV 60 or SSV 60 ) indicate settling time. A
sample of activated biosolids is taken from the aeration tank, poured into a 2000-mL graduated
cylinder, and allowed to settle for 30 or 60 min. The settling characteristics of the biosolids in the
graduated cylinder give a general indication of the settling of the MLSS in the final clarifier. From
the settleability test, the percent settleable solids can be calculated using the following equation:

Settledsolids(mL)
2000

%Settleable solids = ×100 (24.179)

-mLsample

■ EXAMPLE 24.146
Problem: The settleability test is conducted on a sample of MLSS. What is percent settleable solids
if 420 mL settle in the 2000-mL graduated cylinder?

Solution:

420 mL
2000 mL

%Settleable solids = × 100 = 21%