Wastewater: Activated Sludge – Pinfloc

Pin-floc in activated sludge may be defined as very fine floc particles with poor settling characteristics.

Pin-floc/deflocculation may be assessed through visual observation:

  • Carryover of very fine material in final effluent
  • Turbid or milky appearance of final effluent
  • Bacterial flocs have disintegrated into tiny ‘pinhead sized’ particles;
  • Filaments not predominant (microscopic examination)
  • Settleability test may show some well-settling material but a cloudy supernatant; no change on prolonged settling

Principal causes:

  • Extreme underloading (F/M very low)
  • Presence of toxic substances

Correction strategy:

  • Examine the operating record – over an extended time period – for prolonged low F/M.
  • Check available records for the presence of toxic substances in the raw wastewater.
  • Correct the relevant adverse factor.
  • If a tendency to pin-floc/deflocculation persists at a low level addition of a settling aid (e.g. polyelectrolyte) may be required.

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