Activated sludge settling problem resolved
description
Transcript of Activated sludge settling problem resolved
Activated sludge settling problem resolved
Al ParrellaWestern Lake Superior Sanitary
District
Sludge storage
Anaerobic digesters
Flare
Duluth influentKnowlton sta. Influent (industrial flow)
Oxygen production
Liq. O2 storage
Unox reactors
Biofilter
Secondary settling tanks
Flocculation tanks
Multimedia filters
Chlorine contact tanks
Dechlorination
Effluent
Sludge thickeners
Boilers (LP steam)
Dewatering centrifuges Grit removal
Screening
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
• High sludge blanket levels• Thin sludge• Appearance of settleometer• Other indicators to follow:
Return sludge solids concentration
Thickened sludge solids concentration (sludge sent to digestion)
Operating parameters, centrifugesMonth/parameter % capture Polymer dosage,
lb./ton active% cake solids
December 2012 85 56 24
January 2013 98 46 25
February 2013 98 49 26
Operating parameters, centrifugesMonth/parameter % capture Polymer dosage,
lb./ton active% cake solids
December 2012 85 56 24
January 2013 98 46 25
February 2013 98 49 26
Problem
What started it all?
• Problem with dewatering centrifuge polymer system
• Common to both centrifuges– Corrected early January
SVI values December-February (2012-2013)
Mechanical problem repaired here
SVI values December-February (2012-2013)
Mechanical problem repaired here
Activated sludge process adjustment made here
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
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!
Adjustment made to number of Unox reactors in service
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)
Through it all
• Only effluent limit that we struggled with was phosphorus– But we met all limits