Environmental Engineering Reference
In-Depth Information
Example 5.7
Problem:
The monthly average grit removal is 2.5 ft
3
/MG. If the monthly
average flow is 2,500,000 gpd, how many cubic yards must be available
for grit disposal if the pit is to have a 90-day capacity?
Solution:
First, calculate the grit generated each day:
2.5ft3
MG
3
×
2.5MGD
=
6.25 ft /day
The cubic feet of grit generated for 90 days would be:
3
6.25 ft
day
3
×
90 days
=
562.5ft
Convert cubic feet of grit to cubic yards of grit:
3
562.5ft
27 ft /yd
3
=
21 yd
3
3
5.3.4 Chemical addition
Chemical addition is made (either via dry chemical metering or
solution feed metering) to the wastestream to improve settling, reduce
odors, neutralize acids or bases, reduce corrosion, reduce BOD
5
, improve
solids and grease removal, reduce loading on the plant, add or remove
nutrients, add organisms, or aid subsequent downstream processes.
The particular chemical and amount used depend on the desired
result. Chemicals must be added at a point where sufficient mixing will
occur to obtain maximum benefit. Chemicals typically used in wastewa-
ter treatment include chlorine, peroxide, acids and bases, mineral salts
(e.g., ferric chloride, alum), and bioadditives and enzymes.
5.3.4.1 Operational Considerations
When adding chemicals to the wastestream to remove grit, the
operator monitors the process for evidence of mechanical problems and
takes proper corrective actions when necessary. The operator also mon-
itors the current chemical feed rate and dosage. The operator ensures
that mixing at the point of addition is accomplished in accordance with
standard operating procedures and monitors the impact of chemical
addition on influent.
