Title: A New Activated Sludge Process Control Test Uncovers Secondary Clarifier Inefficiencies
1A New Activated Sludge Process Control Test
Uncovers Secondary Clarifier Inefficiencies
- by
- E.J. Wahlberg, S. Biesterfeld,
- G. Farmer, D. Kinnear, L. Robb
2The 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
3L/E WWTP Process Schematic
4Process Objectives in TF/SC and Activated Sludge
- To grow a biomass that
- Flocculates
- Settles
- Compacts
5Typical 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.
6Modified 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
7Sludge Quality Measurements
- SSV5 Settling characteristic
- SSV30 Compacting characteristic
- Supernatant TSS Flocculating characteristic
8Common Sludge Quality Parameter Highly Variable
9Flocculated Suspended Solids
- Supernatant TSS (FSS) indicates effluent TSS
possible with a perfect secondary clarifier. - Difference between FSS and TSS measures clarifier
inefficiency
10Change Stabilizes Sludge But Not Effluent Quality
Change in Operational Strategy
11Wastewater Temperature Affects Secondary
Clarifier Performance
12Conclusions
- 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