A new activated sludge process control test uncovers secondary clarifier inefficiencies
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A New Activated Sludge Process Control Test Uncovers Secondary Clarifier Inefficiencies. by E.J. Wahlberg, S. Biesterfeld, G. Farmer, D. Kinnear, L. Robb. The Littleton/Englewood WWTP. Constructed in 1977 as 20 mgd pure oxygen activated sludge plant

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A New Activated Sludge Process Control Test Uncovers Secondary Clarifier Inefficiencies

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A new activated sludge process control test uncovers secondary clarifier inefficiencies

A New Activated Sludge Process Control Test Uncovers Secondary Clarifier Inefficiencies

by

E.J. Wahlberg, S. Biesterfeld,

G. Farmer, D. Kinnear, L. Robb


The littleton englewood wwtp

The Littleton/Englewood WWTP

  • Constructed in 1977 as 20 mgd pure oxygen activated sludge plant

  • Modified in 1993 to a 32 mgd trickling filter/ activated sludge plant (TF/AS)

  • Upgraded in 1999 to a 36.3 mgd trickling filter/solids contact plant (TF/SC)

  • Currently in pre-design for 50 mgd TF/SC


L e wwtp process schematic

L/E WWTP Process Schematic


Process objectives in tf sc and activated sludge

Process Objectives in TF/SC and Activated Sludge

To grow a biomass that:

  • Flocculates

  • Settles

  • Compacts


Typical approach to activated sludge control inappropriate

Typical Approach to Activated Sludge Control Inappropriate

  • “Performance in the activated sludge process is typically measured by monitoring secondary clarifier effluent for TSS, BOD, COD….”

  • Inappropriate: effluent quality includes secondary clarifier inefficiencies.


Modified settleometer test

Modified Settleometer Test

  • Collect secondary clarifier and mixed liquor effluent samples

  • Pour mixed liquor sample into square flocculation jar

  • Mix for 30 minutes at 50 rpm

  • Settle for 30 minutes

  • Record 5 and 30 minute SSV

  • Collect supernatant sample

  • Analyze supernatant and effluent samples for TSS


Sludge quality measurements

Sludge Quality Measurements

  • SSV5: Settling characteristic

  • SSV30: Compacting characteristic

  • Supernatant TSS: Flocculating characteristic


Common sludge quality parameter highly variable

Common Sludge Quality Parameter Highly Variable


Flocculated suspended solids

Flocculated Suspended Solids

  • Supernatant TSS (FSS) indicates effluent TSS possible with a perfect secondary clarifier.

  • Difference between FSS and TSS measures clarifier inefficiency


Change stabilizes sludge but not effluent quality

Change Stabilizes Sludge But Not Effluent Quality

Change in

Operational Strategy


Wastewater temperature affects secondary clarifier performance

Wastewater Temperature Affects Secondary Clarifier Performance


Conclusions

Conclusions

  • SSV30 (SVI) may not be appropriate for control

  • FSS better control parameter than TSS

  • Secondary clarifier inefficiencies result in TSS increase between 2 and 10 mg/L

  • Secondary clarifier inefficiency increases with decreasing wastewater temperature


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