Filaments and Bacteria...
Volume - 7...

Appendix - 1...

Bulking Sludge...

A phenomenon, which occurs in, activated sludge plants when sludge/biomass occupies an excessive volume and does not settle readily so that in extreme cases the effluent from the final settlement tank contains an excessive amount of suspended solids. It is usually associated with the presence and predominance of filamentous micro-organisms in the biomass.

To Be More Specific :
- The SSVI ( Stirred Specific Volume Index ) is greater than 150 ml/gram.
( Less than 150 ml/gram = "Good Settlement" and greater than 250 ml/gram = "Poor Settlement" )
- Sludge settles slowly.
- Sludge does not thicken readily.
- Sludge contains large numbers of filamentous micro-organisms.
- Water associated with sludge quality is high with respect to BOD.

Reasons for Bulking Occuring...

- Insufficient dissolved oxygen for long periods of time. Do less than 0.5 mg/l ( Should be 1.0 – 3.5 mg/l ).
- Septic sewage e.g. presence of sulphides.
- Low pH. pH should be 6.0 – 8.0 ( Low pH can lead to fungal selection ).
- Low F:M ratio i.e. Food is diminishing, biomass is increasing, F/M should be greater than 0.05, normally.
- Influent nutrient levels are low. Ideally C : N : P should be 100 : 5 : 1. ( C is normally BOD C ).
- Other trace metals may also be missing e.g. Iron, Sulpur.

Filament Types as Indicators of Conditions Causing Activated Sludge Bulking...

Suggested Causative Condition	Indicator Filament Type
Low D.O. ( For the applied organic loading )	S.natans, Type 1701 and H.hydrossis
Low Organic Loading Rate ( F:M ) ( In completely mixed aeration basins )	M.parvicella, Nocardia species, H.hydrossis, Type 021N, Type 0041, Type 0675, Type 0092, Type 0581, Type 0961 and Type 0803
Septic Wastes / Sulphides	Thiothrix species, Beggiatoa species, Type 021N
Nutrient Deficiency ( N and / or P )	Thiothrix species, Type 021N, Type 0041 and Type 0675
Low pH ( Below pH 6.5 )	Fungi