Cooper J, Cass J, Rogers M and Smith S R.
Centre for Environmental Control and Waste Management, Department of Civil and Environmental
Engineering, Imperial College London, UK


Previous work reported at the 2003 European Biosolids and Organic Residuals Conference (Paper 77) showed a significant increase in numbers of Escherichia coli after dewatering liquid primary digested sludge by centrifugation, potentially exceeding the microbiological standard of 105 E. coli g-1 dry solids (DS) for agricultural use. This paper reports a follow up investigation of the effects of different types of dewatering process on E. coli enumeration in conventionally treated, anaerobically digested sludge (primary and secondary liquid digestion), as well as raw sludge at eight wastewater treatments works. The dewatering methods evaluated included: centrifuge conditioning, and filter-belt and filter-plate pressing. The results demonstrated that conventional treatment by primary and secondary liquid digestion and dewatering conditioning produces biosolids compliant with proposed UK maximum microbiological limits for agricultural application.

KEY WORDS Agriculture, Biosolids, Centrifuge, Dewatering, Escherichia coli, Recycling, Sewage Sludge.

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