Introduction to the Safe Sludge Matrix

Brian Chambers, Adas


The landmark agreement between Water UK representing the Water Industry and the British
Retail Consortium representing the major retailers in September 1998, resulted in the
production of the “Safe Sludge Matrix” (commonly referred to as the ADAS Matrix), which
transformed sewage sludge (biosolids) recycling practices to agricultural land. The Matrix
consists of a table of crops and levels of sewage sludge treatment, with guidance on the
treatment level acceptable for each crop type. Two standards of treatment (“Conventional”
and “Enhanced”) are referred to in the Matrix based on pathogen reduction levels (using
E.coli as an indicator organism) of 2-log10 and 6-log10, respectively.

The hazard analysis and critical control point (HACCP) approach to pathogen risk
management was adopted by the Water Industry, with critical control points measured and
audited during each treatment process. As a result of the Matrix, all untreated sludges were
banned from application to land used to grow food or animal feed crops from 31 December
1999. The Director General of Water Services of OFWAT announced in 1999 that Water
Companies would need to spend over £400 million between 2000-2005 to improve sewage
sludge recycling and recovery, much of this being on new treatment processes in order to
phase out the use of untreated sludge.

Sewage sludge, biosolids, pathogens, Safe Sludge Matrix.

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