Field and laboratory investigations quantifying the factors responsible for enteric pathogen decay in biosolids amended agricultural soils
Author(s)
Cass, James
Type
Thesis
Abstract
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.
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.
Date Issued
2009-05
Date Awarded
2010-01
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Smith, Stephen
Sponsor
EPSRC, DEFRA, NFU, UKWIR, Anglian Water, Scottish Water, Thames Water, Yorkshire Water
Creator
Cass, James
Publisher Department
Civil and Environmental Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)