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

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

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

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

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

7. Return sludge solids concentration

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

9. Operating parameters, centrifuges
Month/parameter
% capture
Polymer dosage, lb./ton active
% cake solids
December 2012 85 56 24
January 2013 98 46 25
February 2013 49 26

10. Operating parameters, centrifuges
Month/parameter
% capture
Polymer dosage, lb./ton active
% cake solids
December 2012 85 56 24
January 2013 98 46 25
February 2013 49 26
Problem

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

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

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

14. 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

15. 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!

16. Adjustment made to number of Unox reactors in service

21. 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)

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