In treatment of sewage one process used is the activated sludge process in which air is passed through a mixture of sewage and old sludge to allow the micro-organisms to break down the organic components of the sewage. Sludge is continually drawn off as new sewage enters the tank and this sludge must then be settled so that the supernatant can be separated to pass on to further stages of treatment.
Filamentous microorganisms grow in long strands that have much greater volume and surface area than conventional floc and are very slow to settle. Under certain growing conditions, filamentous organisms predominate. There is little robust scientific evidence that can be used to avoid sludge bulking but what there is indicates that over-loading works, having a carbohydrate rich input and having too low a recycle rate may all contribute.
To avoid sludge bulking some of the flow that enters the reactor can be by-passed, recycle ratio can be increased, lime or soda can be added to the reactor or the re-aeration rate increased.
- C. C. Lee and Shun Dar Lin (2007). Handbook of environmental engineering calculations (2nd ed.). McGraw-Hill Professional. p. 1.550. ISBN 0-07-147583-4. More than one of
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- Orris E. Albertson (1992). "Control of Bulking and Foaming Organisms". In Clifford W. Randall and James Lang Barnard. Design and retrofit of wastewater treatment plants for biological nutrient removal. CRC Press. ISBN 0-87762-922-6. Unknown parameter
- Jiri Wanner (1994). Activated Sludge Bulking and Foaming Control. CRC Press. ISBN 1-56676-121-2. More than one of
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