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

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 Secondary Clarifier Inefficiencies

  • 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 Secondary Clarifier Inefficiencies


Process objectives in tf sc and activated sludge
Process Objectives in TF/SC and Activated Sludge Secondary Clarifier Inefficiencies

To grow a biomass that:

  • Flocculates

  • Settles

  • Compacts


Typical approach to activated sludge control inappropriate
Typical Approach to Activated Sludge Control Inappropriate Secondary Clarifier Inefficiencies

  • “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 Secondary Clarifier Inefficiencies

  • 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 Secondary Clarifier Inefficiencies

  • SSV5: Settling characteristic

  • SSV30: Compacting characteristic

  • Supernatant TSS: Flocculating characteristic


Common sludge quality parameter highly variable
Common Sludge Quality Parameter Highly Variable Secondary Clarifier Inefficiencies


Flocculated suspended solids
Flocculated Suspended Solids Secondary Clarifier Inefficiencies

  • 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 Secondary Clarifier Inefficiencies

Change in

Operational Strategy



Conclusions
Conclusions Performance

  • 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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