Pathogen Inactivation In Biosolids-Amended Agricultural Soils

Smith, S.R., Cass, J., Perez-Viana, F. and Rogers, M.
Imperial College London


The decay of enteric pathogens in soil is a critical component of the multi-barrier approach to protect human health when
biosolids are applied to agricultural land as a fertiliser. General information on the mechanisms responsible for the inactivation
of enteric organisms in soil is available, but specific quantitative data on the processes involved and long-term monitoring of
the decay kinetics in field soil are limited. Ecological processes may have a critical role in eliminating enteric bacteria applied
to soil in biosolids providing an active mechanism for their removal. To test this hypothesis, and to provide long-term decay
information, a series of field experiments have been established on two contrasting soil types of different organic matter and
fertility status, amended with different sludge types. The population of the indicator organism, Escherichia coli, was
enumerated. Inoculation treatments with a non-verotoxigenic strain of E. coli O157 were also monitored and the soil microbial
biomass concentration and protozoa populations, which are important soil predators, were measured. E. coli and E. coli O157
declined to background or non-detectable concentrations generally within 60 days of sludge incorporation. The relationship
between pathogen inactivation and soil ecological processes and fertility is discussed. The results provide assurance that
assumptions relating to soil decay during waiting periods stipulated for agricultural use of sludge are highly conservative and
they confirm that the cropping/harvesting restrictions prescribed in legislation and guidance controlling the application of
biosolids on farmland allow the natural attenuation of pathogens to protect human health with a significant margin of safety.

Agriculture, Biosolids, Escherichia coli, Pathogen, Protozoa, Recycling, Sewage sludge, Soil

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