Wastewater: Activated Sludge – Bulking

Sludge bulking may be noted through visual observation:

  • Failure of sludge solids to settle in the final clarifier
  • Carryover of solids resulting in high effluent suspended solids
  • Presence of filamentous bacteria (microscopic examination)
  • Increased SVI and disimproved settleability
  • Clear supernatant liquor after prolonged settling

Principal causes:

  • Underloading 
  • Dissolved oxygen too low
  • Nutrient deficiency

A correction strategy can be developed after reviewing:

  • F/M and SVI (or cone settleability) against Time
  • Dissolved oxygen and SVI (or cone settleability) against Time
  • Nutrient supply and SVI (or cone settleability) against Time

It may take a number of weeks for serious bulking (predominance of filaments) to become established.  Therefore the data must be available to trace key process control paramaters back in time to establish when the problem began to develop.

  • Once the cause has been established an appropriate correction strategy can be implemented.

ECOS Environmental Consultants Limited