Water/Wastewater Laboratory Calculations - Basic Mathematics for Water and Wastewater Operators - page 239

amounts. Keeping in mind that normality is a measure of the reacting power of a
solution (i.e., 1 equivalent of a substance reacts with 1 equivalent of another sub-
stance), we use the following equation to determine normality:

Normality ( N ) = No. of equivalents of solute ÷ Liters of solution (16.11)

■ Example 16.11
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. of equivalents of solute ÷ Liters of solution = 2.0 equivalents ÷ 1.5 L = 1.33 N

■ Example 16.12
Problem: An 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:

No. of equivalents of solute ÷ Liters of solution = 1.6 equivalents ÷ 0.8 L = 2 N

SETTLEABILITY (ACTIVATED BIOSOLIDS SOLIDS)
The settleability test is a test of the quality of the activated biosolids solids—or acti-
vated sludge solids (mixed-liquor suspended solids, MLSS). 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 calcu-
lated using the following equation:

Settledsolids(mL)
2000

%Settleable solids = ×100 (16.12)

-mLsample