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 PowerPoint PPT Presentation


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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

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

  • 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


Process Objectives in TF/SC and Activated Sludge

To grow a biomass that:

  • Flocculates

  • Settles

  • Compacts


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

  • 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

  • SSV5: Settling characteristic

  • SSV30: Compacting characteristic

  • Supernatant TSS: Flocculating characteristic


Common Sludge Quality Parameter Highly Variable


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 in

Operational Strategy


Wastewater Temperature Affects Secondary Clarifier Performance


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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