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A New Twist on an Old Test for Activated Sludge Process Control

A New Twist on an Old Test for Activated Sludge Process Control. Estes Park PWO Seminar October 22, 2004 Greg Farmer – Littleton / Englewood WWTP. L/E WWTP Process Schematic. Aerial View. Phase 2 Construction Project. Phase 2 Construction Project. TF/SC.

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A New Twist on an Old Test for Activated Sludge Process Control

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  1. A New Twist on an Old Test for Activated Sludge Process Control Estes Park PWO SeminarOctober 22, 2004 Greg Farmer – Littleton / Englewood WWTP

  2. L/E WWTP Process Schematic

  3. Aerial View

  4. Phase 2 Construction Project

  5. Phase 2 Construction Project

  6. TF/SC • 40 – 70% of SBOD and 25 – 50% of CBOD is removed in the trickle filter • Aeration basins provide remaining BOD removal and flocculation • SRT < 2 days • SVI around 100 • Not intended for nutrient removal

  7. Typical Activated Sludge Control Methods • Control MLSS Inventory • Dissolved oxygen concentration • And RAS/clarifier blankets To produce a sludge that: • Flocculates • Settles • Compacts

  8. Traditional Performance Indicators • Secondary clarifier effluent TSS and BOD • Final effluent TSS and BOD • SVI / Settleometer • SRT • F/M

  9. But, what if…….. • What if your secondary clarifiers do not function properly due to hydraulic and/or flocculation deficiencies • Too shallow • Short circuiting • RAS return problems • Poor sampling location • Thermal Currents • Floc shear

  10. Final Effluent TSS Secondary Clarifier TSS

  11. Temperature Temperature plays a major role: • Biological activity decreases by 50% for every 10° C drop in temperature • Clarifier thermal currents are created with as little as a 0.5° C temperature difference

  12. Final Effluent TSS Secondary Clarifier TSS

  13. Aeration Basin Temperature Swing

  14. Thermal Currents

  15. What Tools Are Available? • Does a tool exist that can be used to predict or forecast the correct MLSS inventory to maintain a healthy biomass? • This tool must not look at deficiencies in the secondary clarifiers

  16. Enter the Wally Meter • Developed by Dr. Eric Wahlberg as the Wahlometer • Consider it a “flocculated settleometer” • Determines the “health” of an activated sludge • Negates the influence of secondary clarifier inefficiencies on process control decisions

  17. Wally Meter in Action Wally Meter • Collect a MLSS grab sample 2 times/day • Pour into square Phipps and Bird flocculation jar or authentic “Wahlometer” • Mix at 50 rpm for 30 minutes • Record the 5 minute SSV5 reading • Settle for 30 minutes and record the 30 minutes SSV30 reading to calculate SVI • Sample subnatant for TSS and/or NTU

  18. Wally Meter Terms • ESS – Effluent Suspended Solids • FSS – Flocculated Suspended Solids, SS that remain in the subnatant after 30 minutes of settling preceded by 30 minutes of flocculation

  19. Clarifier ESS vs. Wally Meter FSS

  20. How to Use the Data • The Wally Meter TSS value is the lowest possible TSS value that can be attained in a perfect environment • Adjust MLSS to maintain low Wally Meter TSS • Adjust seasonally for temperature changes

  21. The Equation Inventory = (21,000lbs MLSS + ((Avg Wally Meter TSS – 6) * 500)) +(21.5 C – Avg Basin temp.) * Lbs MLSS Inventory * .1) - (5-minute Wally Meter reading – 400) * 20

  22. The Equation

  23. Predictive Chart Spreadsheet

  24. Last 45 Days

  25. Final Effluent

  26. Applicability • Will the equation work for an activated sludge plant? A BNR plant? • Collect data for a period of time • Experiment with equation values to attain a fit

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