Proceedings

Reducing numbers of pathogenic bacteria is one of the chief objectives when treating sewage sludge for land application.  E. coli is used by the water industry as an indicator organism to signal the presence of enteric bacterial pathogens, and as such numbers of this indicator are used to determine the microbiological quality of sludge in HACCP monitoring.  It has been known for several years that numbers of E.coli in treated sludge can often increase dramatically upon dewatering and in subsequent cake storage.  This alarming phenomenon has been termed ‘E. coli regrowth’, and so far little is known about its causes and mechanisms. This report summarises the findings of some recent investigations into the effects of different parameters on E.coli die-off and regrowth at bench and full scale with the aim to further the understanding of this phenomenon.