Environmental Engineering Reference
In-Depth Information
10.6.1.1 Aerobic Digester Process Control Calculations
Wastewater operators who operate aerobic digesters must make
certain process control calculations. Moreover, licensing examinations
typically include aerobic digester problems for determining volatile sol-
ids loading, digestion time, digester efficiency, and pH adjustment. These
process control calculations are explained in the following sections.
10.6.1.1.1 volatile Solids loading
Volatile solids loading for the aerobic digester is expressed in
pounds of volatile solids entering the digester per day per cubic foot of
digester capacity:
Volati
le Solids Added(lb/day)
Digester Volume (ftt)
3
=
Volatile Solids Loading(lb/day/ft )
(10.16)
3
Example 10.16
Problem:
The aerobic digester is 25 ft in diameter and has an operating
depth of 24 ft. The sludge added to the digester daily contains 1350 lb of
volatile solids. What is the volatile solids loading in pounds per day per
cubic foot?
Solution:
1350lb/day
.7825f
0.11 lb/day/ft
3
Volatile Solids Loading
=
=
× tt25ft24ft
×
×
10.6.1.1.2 digestion Time in days
Digestion time is the theoretical time the sludge remains in the
aerobic digester:
Digester Volume (gal)
DigestionTime(days)
=
(10.17)
Sludge Added(gpd)
Example 10.17
Problem:
The digester volume is 240,000 gal. Sludge is being added to
the digester at the rate of 13,500 gpd. What is the digestion time in
days?
Solution:
240,000 gal
13,500gpd
DigestionTime
=
=
17.8 d
ays
