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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 TankSludge settles and stays down for at
least an hour5min-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 TankSludge settles slowly or not at all-5
min reading is above 80%Sludge settles too fast-5 min reading
below 40%Poor color-
black(septic),red(overaerated)Settled sludge rises in less than hourSupernatant 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