Science of Water : Concepts and Applications

Water Treatment Calculations 355
Solution:
settled biosolids, mL
% Settled biosolids
100
total sample, mL
22 mL
100
100 mL
22%
settled biosolids
Example 10.55
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, mL
% Settled biosolids
100
total sample, mL
21 mL
100
100 mL
21% settled biosolids
DETERMINING LIME DOSAGE, mg/L
– During the alum dosage process, lime is sometimes added to provide adequate alkalinity (HCO3 )
in the solids contact clarifi cation process for the coagulation and precipitation of the solids. To
determine the lime dose required, in mg/L, three steps are required.
In Step 1, the total alkalinity required is required is calculated. Total alkalinity required to
react with the alum to be added and provide proper precipitation is determined using the following
equation:
Example 10.56
Problem:
Total alkalinity required, mg / L alkalinity reacting w/alum, mg / L
alkalinity in the water, mg/L
(1 mgL alum reacts w/0.45 mgL alkalinity)
Raw water requires an alum dose of 45 mg/L, as determined by jar testing. If a residual 30 mg/L alkalinity
must be present in the water to ensure complete precipitation of alum added, what is the total
alkalinity required, in mg/L?
(10.55)