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A New Activated Sludge Process Control Test Uncovers Secondary Clarifier Inefficiencies

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Supernatant TSS: Flocculating characteristic. Common Sludge ... Supernatant TSS (FSS) indicates effluent TSS possible with a perfect secondary clarifier. ... – PowerPoint PPT presentation

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Title: A New Activated Sludge Process Control Test Uncovers Secondary Clarifier Inefficiencies


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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