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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. 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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  1. A New Activated Sludge Process Control Test Uncovers Secondary Clarifier Inefficiencies by E.J. Wahlberg, S. Biesterfeld, G. Farmer, D. Kinnear, L. Robb

  2. 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

  3. L/E WWTP Process Schematic

  4. Process Objectives in TF/SC and Activated Sludge To grow a biomass that: • Flocculates • Settles • Compacts

  5. 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.

  6. 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

  7. Sludge Quality Measurements • SSV5: Settling characteristic • SSV30: Compacting characteristic • Supernatant TSS: Flocculating characteristic

  8. Common Sludge Quality Parameter Highly Variable

  9. Flocculated Suspended Solids • Supernatant TSS (FSS) indicates effluent TSS possible with a perfect secondary clarifier. • Difference between FSS and TSS measures clarifier inefficiency

  10. Change Stabilizes Sludge But Not Effluent Quality Change in Operational Strategy

  11. Wastewater Temperature Affects Secondary Clarifier Performance

  12. 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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