Environmental Engineering Reference
In-Depth Information
Corrective actions:
Adjust skimmer speed to allow concentration
to occur; stop sludge flow through the unit and purge with recy-
cles flow; determine proper chemical dose and adjust; reduce air-
flow to pressurization tank; identify malfunction and correct.
•
The dissolved air concentration is too low.
Causal factor:
Mechanical malfunction has occurred.
Corrective action:
Identify cause and correct.
symptom 2.
•
symptom 3.
Effluent (subnatant) flow contains excessive solids.
Causal factors:
Unit is overloaded; chemical dose is too low; skim-
mer is not operating; solids-to-air ratio is low; solids have built up
in the thickener.
Corrective actions:
Turn off sludge flow; purge unit with recy-
cle; determine proper chemical dose and flow; turn skimmer on;
adjust skimmer speed; increase airflow to pressurization sys-
tem; remove sludge from the tank.
10.5.4 sludge Thickening Process Control Calculations
Sludge thickening calculations are based on the concept that the
solids in the primary of secondary sludge are equal to the solids in the
thickened sludge. Assuming that a negligible amount of solids is lost in
the thickener overflow, the solids are the same. Note that the water is
removed to thicken the sludge and result in higher percent solids.
10.5.4.1 Estimating Daily Sludge Production
Equation 10.10 provides a method for establishing an initial pump-
ing rate or evaluating the adequacy of the current pump rate:
⎡
⎣
⎢
(Influent TSS Conc.
− luent TSS Conc.)
Flow (MGD)
Eff
⎤⎤
⎦
⎥
×
×
8.34 lb/gal
Est. Pump
Rate (gpm)
(10.10)
=
% Solids in Sludge
×
8.34 lb/gal
×
1440 min/day
Example 10.10
Problem:
The sludge withdrawn from the primary settling tank contains
1.5% solids. The unit influent contains 280 mg/L TSS, and the effluent
contains 141 mg/L. If the influent flow rate is 5.55 MGD, what is the esti-
mated sludge withdrawal rate in gallons per minute (assuming the pump
operates continuously)?
Solution:
(280 mg/L
−
141mg/L)
× 5.55 MGD8.34lb/gal
×
Sludge Withdrawal Rate
=
0.015
×
8.34 lb/gal
×
1440
min/day
=
36 gpm
