Operator
Observations
Troubleshooting Activated Sludge
Problems
Jim Winslade – Adjunct Instructor
ERTC -SIUE
Aeration Tank Problems
Surface Turbulence should be even
over entire surface of aeration tank
- Dead spot would indicate plugged
diffuser
- Violent turbulence in one spot
indicates broken air header or missing
diffuser

Aerator Pattern
Change in Aeration Pattern
Aeration Basin Foaming
Stiff White, billowing foam indicates an
overloaded plant – Young sludge
- Decrease wasting – Build Mixed Liquor
 Excessive Brown Foam – thick and greasy
in appearance
- Plant is under-loaded or sludge is too old –
Nocardia Foam
- Increase wasting – reduce mixed liquor

Stiff White Foam
Thick Brown Greasy Foam
Crisp Brown or White Foam

A small amount of
crisp brown or
white foam on the
aeration basin
surface is an
indicator of normal
conditions
Clarifier Problems
Solids Washout – sludge solids being
carried over the weirs of clarifier
- Hydraulic Overload
- Solids Overload
- Equipment Malfunction – return
sludge pump or collector
- Temperature currents

Solids Washout
Bulking Sludge
True Bulking – Sludge fills clarifier and
overflows weirs into effluent – plant is
overloaded and sludge is young –
overaeration may aggravate
 Filamentous Bulking – Very clear
layer of water over sludge filling
clarifier and overflowing weirs –
caused by filamentous bacteria

Filamentous Bulking
Filamentous bulking results from
filamentous bacteria preventing the
proper settling and compaction of
sludge floc
-Low DO
-low nutrients in influent
-low pH
-warm temperature

Bulking Sludge
Sludge Clumping
Clumps of sludge rise up through
clear supernatant in clarifier and burst
at the surface
- Sludge is sitting too long in the
clarifier and denitrification is starting
Nitrogen gas builds up in sludge and
carries it to the surface

Sludge Clumping
Sludge sitting in clarifier too long –
sludge return rate is too low –
increase pumping rate slightly
 Sludge is too old – increase wasting

Sludge Clumping
Solids in Effluent (Cloudy)
Ashing –small ash-like particles on surface
of clarifier
- Start of denitrification
- High grease content
 Pin Floc – small dense particles of floc
- Old sludge breaking down
 Straggler Floc – Light fluffy sludge particles
- Young sludge, low mixed liquor

Ashing
Pin Floc
Straggler Floc
Settling Test





1000 ml
graduated
cylinder(wall
effect)
Glass Jar
2 Liter Beaker
Settleometer
Clarifier Problems
Settleability
Aeration Tank, but may be done on
return sludge from the clarifier
 Use only a fresh sample
 Don’t take sample from dead spot,
corner or wall
 If filamentous bulking is suspected,
two settleometers may be set up. One
settleometer sample is diluted 50%
with effluent. If both settleometers
settle at same rate or do not settle,
filamentous bulking is likely

Settleometer
Well Operating Plant

Aeration Tank
Sludge settles and stays down for at
least an hour
 5min-50 to 70%, 30min-34 to 50%,
and 60min-30 to 40%
 Supernatant clear


Clarifier-as clear and solids free as
possible
Poor Operating Plant

Aeration Tank
Sludge settles slowly or not at all-5
min reading is above 80%
 Sludge settles too fast-5 min reading
below 40%
 Poor colorblack(septic),red(overaerated)
 Settled sludge rises in less than hour
 Supernatant is murky or turbid

Slow Settling
Oxygen Uptake Rate
Measure of the uptake of oxygen by
the mixed liquor
 Rapid rate indicates Young Sludge or
High F/M
 Low rate indicates Old Sludge or Low
F/M
 Zero Rate indicates Toxic substance
has harmed or killed microbes

OUR Procedure
Obtain fresh mixed liquor sample
 Saturate sample with air by shaking in
closed partially filled container
 Pour sample into BOD bottle and
insert DO probe (BOD bottle probe)
 Record decrease in DO in mg/l over
10 min.
 Calculate oxygen uptake

O2 Uptake Rate Calculation
Subtract Ending DO (10 min) from
initial DO (0 min)
 Divide by 10 for 10 min time period
 Multiply by 60 to determine uptake
rate per hour
 To determine Specific Oxygen Uptake
Rate or respiration rate divide rate by
MLSS concentration in grams(SOUR)

Specific Oxygen Uptake Rate
Process Control Levels

Activated Sludge


20-30 mg/L/hr
Aerobically digested sludge

1.5 mg/L/hr or less indicates that the
sludge has stabilized