Proceedings

The introduction of the Sludge (Use in Agriculture) Regulations and the subsequent implementation of HACCP procedures have resulted in the Water Companies analysing very large numbers of sludge and biosolids samples to determine pathogen indicator content. This case study reports on the experience of South West Water’s HACCP Team and laboratory service of the introduction of the Colilert-18/QuantiTray2000 (TM IDEXX Laboratories) defined substrate Most Probable Number (MPN) quantitative method for Escherichia coli (E coli) determination. The Colilert method offered improved detection limits, reduced laboratory resource requirements and a more speedy result. After a period of validation and accreditation, the method became routine in January 2004 replacing both the LTBBP MPN method and MLGA chromogenic agar methods previously employed. Within weeks, anomalous results were observed suggesting significantly increased concentrations of E coli in the treated biosolids. This case study presents the findings of the investigation launched to discover the reasons for the unusual results.

KEY WORDS Agriculture analysis Biosolids Colilert E.coli HACCP pathogen Regulations sludge