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