Operational Problems

Troubleshooting Activated Sludge
Jim Winslade – Adjunct Instructor
Aeration Tank Problems
Surface Turbulence should be even
over entire surface of aeration tank
- Dead spot would indicate plugged
- Violent turbulence in one spot
indicates broken air header or missing
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
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
Pin Floc
Straggler Floc
Settling Test
1000 ml
Glass Jar
2 Liter Beaker
Clarifier Problems
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
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
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
 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

similar documents