Environmental Engineering Reference
In-Depth Information
Table 8.1 aCTivaTed sludge ModifiCaTions
Contact
stabilization
extended
aeration
oxidation
ditch
Parameter
Conventional
Aeration time (hr)
4-8
0.5-1.5
(contact)
3-6
(reaeration)
24
24
Settling time (hr)
2-4
2-4
2-4
2-4
Return rate
(% of influent flow)
25-100
25-100
25-100
25-100
MLSS (mg/L)
1500-4000
1000-3000
3000-8000
2000-6000
2000-6000
DO (mg/L)
1-3
1-3
1-3
1-3
SSV
30
(ml/L)
400-700
400-700
(contact)
400-700
400-700
Food-to-mass ratio
(lb BOD
5
/lb MLVSS)
02-0.5
0.2-0.6
(contact)
0.05-0.15
0.05-0.15
MCRT
(whole system, days)
5-15
N/A
20-30
20-30
% Removal BOD
5
85-95%
85-95%
85-95%
85-95%
% Removal TSS
85-95%
85-95%
85-95%
85-95%
Primary treatment
Yes
No
No
No
Table 8.1 lists the process parameters for each of the four most
commonly used activated sludge modifications.
8.9 aCTivaTed sludge
ProCess ConTrol ParaMeTers
When operating an activated sludge process, the operator must be
familiar with the many important process control parameters that must
be monitored frequently and adjusted occasionally to maintain optimal
performance.
8.9.1 alkalinity
Monitoring alkalinity in the aeration tank is essential to control
of the process. Insufficient alkalinity will reduce organism activity and
may result in low effluent pH and, in some cases, extremely high chlo-
rine demand in the disinfection process.
8.9.2 dissolved oxygen
The activated sludge process is an aerobic process that requires
some dissolved oxygen (DO) to be present at all times. The amount of
oxygen required is dependent on the influent food (BOD), the activity of
the activated sludge, and the degree of treatment desired.
