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Activated sludge settling problem resolved

Activated sludge settling problem resolved. Al Parrella Western Lake Superior Sanitary District. Typical SVI values. 65-70 range (annual average). SVI values December-February (2012-2013). SVI values December-February (2012-2013). Trouble above this line. Problems in plant.

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Activated sludge settling problem resolved

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  1. Activated sludge settling problem resolved Al Parrella Western Lake Superior Sanitary District

  2. Typical SVI values • 65-70 range (annual average)

  3. SVI values December-February (2012-2013)

  4. SVI values December-February (2012-2013) Trouble above this line

  5. Problems in plant • High sludge blanket levels • Thin sludge • Appearance of settleometer • Other indicators to follow:

  6. Return sludge solids concentration

  7. Thickened sludge solids concentration (sludge sent to digestion)

  8. Operating parameters, centrifuges

  9. Operating parameters, centrifuges Problem

  10. What started it all? • Problem with dewatering centrifuge polymer system • Common to both centrifuges • Corrected early January

  11. SVI values December-February (2012-2013) Mechanical problem repaired here

  12. SVI values December-February (2012-2013) Mechanical problem repaired here Activated sludge process adjustment made here

  13. Initial response to problem • As plant became upset with recycled digested sludge, response was to increase the aeration units in service • This may have been proper to address the amount recycled septic sludge entering the aeration system but caused a classic “low nutrient” problem when the recycle flow stopped

  14. My point: • Even though mechanical problem was resolved in early January we still had deteriorating activated sludge problem because we had too many aeration units in service!

  15. Adjustment made to number of Unox reactors in service

  16. Result of taking reactor off line • BOD was driven deeper into the basins • F/M increased (by roughly 25%) • Sludge regained its darker-brown color • SVI came within range and settling improved in the nick of time (before the spring floods)

  17. Through it all • Only effluent limit that we struggled with was phosphorus • But we met all limits

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