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Title: Field and laboratory investigations quantifying the factors responsible for enteric pathogen decay in biosolids amended agricultural soils
Author: Cass, James
ISNI:       0000 0004 2681 9698
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2010
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The inactivation of enteric pathogens in soil is a critical component of the multibarrier approach to protect human health when biosolids are applied to agricultural land as a fertiliser. Ecological processes may have a central 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 on a variety of enteric pathogens, a series of field experiments was established on two soils of contrasting organic matter and fertility status, amended with different sludge types. E. coli population numbers were monitored in soils amended with biosolids and unamended control soils. Inoculation treatments with E. coli O157, Salmonella enterica, Listeria monocytogenes, Campylobacter jejuni, and Clostridium perfringens were also monitored. E. coli were found to be indigenous to both soils and their populations were highly dynamic. Following application of conventionally treated biosolids, E. coli and enteric pathogen numbers increased and subsequently showed a rapid decline within 20-100 days and were not significantly different from numbers in the unamended control soils within 316 days. E. coli content of enhanced treated biosolids was lower than that of unamended control soils prior to application. However, E. coli numbers in soil treated with enhanced biosolids increased compared to the unamended controls in response to substrates input. Laboratory investigations indicate the direct involvement of the soil ecological processes on E. coli inactivation an in particular, bacteriophagous protozoa activity. These complex mechanisms are actively stimulated by biosolids addition and significantly impact on E. coli decay in biosolids-amended agricultural soils. The results provide assurance that assumptions relating to soil decay during waiting periods stipulated for agricultural use of sludge are highly conservative. They confirm that the cropping/harvesting restrictions prescribed in legislation and guidance controlling the application of biosolids on farmland allow for the natural attenuation of pathogens to protect human health with a significant margin of safety.
Supervisor: Smith, Stephen Sponsor: EPSRC ; DEFRA ; NFU ; UKWIR ; Anglian Water ; Scottish Water ; Thames Water ; Yorkshire Water
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral