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Case Study: Clarifier Scum Mixing

“All Clarifiers Should Not Be Without!”

Scum removal is an important feature for both primary and secondary clarifiers; however, specifications rarely specify agitation to help mix and efficiently transport this scum. Primary clarifier scum consists primarily of fats, oils, grease and other “modern trash” debris. Secondary clarifier scum is the biological foam or the biomass that has floated to the top due to denitrification. In a clarifier, scum removal mechanisms use skimmers that push the scum into a scum pit adjacent to the clarifier. As the pit fills with scum, primary and/or scum pumps pump the contents to the digesters.

 

Problem:

The wastewater utility had to monthly manually vactor out the scum that accumulates from fats, oils and grease trapped in the primary scum trough which was costly, odorous and messy. The existing scum pumps would only pump out the clear liquid beneath leaving a floating scum mat that built up and needed to be vactored out.

BEFORE: Primary Scum Sludge Closeup

BEFORE: Primary Scum Sludge

 

 

 

 

 

 

 

 

 

 

 

 

 

Background of Clarifier Scum :

  • Scum removal is an important feature for clarifiers
  • Primary clarifier scum
    • Fats, oils, grease and other “modern trash” debris.
  • Secondary clarifier scum
    • Biological foam or the biomass that has floated to the top due to denitrification.
  • Skimmers push the scum into a pit adjacent to the clarifier.
  • As the pit fills with scum, contents pumped to digesters.
  • Specs rarely specify agitation to help mix and efficiently transport this scum.

 

Solution:

In the scum pit, installed a Flygt compact 2.5HP submersible mixers on a timer and set to turn on prior to operation of scum pump. The fats, oils, grease (FOG) and floatables are entrained and pumped away and no more need to manually vactoring out four scum pits monthly.

AFTER: Flygt Submersible Mixer mixes Primary Scum

Results:

  • All the troublesome fats, oils, grease (FOG) and floatables were entrained and pumped away.
  • No more need to manually vactor out four scum pits monthly.
  • Saved $3,000 per month
  • Eliminated
    • Odors,
    • Nuisance
    • Messy conditions
  • Happy Operations Staff & Neighbors

 

A Flygt pump with N-hydraulics was installed to retrofit screw induced pumps. The Flygt’s self cleaning impeller to handle the challenging scum/debris without clogging.

Flygt’s Self-Cleaning Pump ideal for handling Primary Scum without clogging