Enteric Pathogen Survival in Sewage Sludge-Amended Agricultural Soil

Reference: 11/SL/06/8
ISBN: 1 84057 604 9
Published Date: 29/09/2011

Biosolids represent the solid fraction of sewage and potentially contain a number of human and animal pathogens. This report describes a series of field trials in which sewage sludge that had been subjected to selected treatment methods was land applied and subsequent pathogen survival assessed.
Nymbers of Escherichia coli in biosolids-amended soils decayed to the background population in field soil within 40-60 days of sludge application. E. Coli O157, Listeria and Salmonella all showed significant decay when introduced to two different soil types in inoculated sludge and were undetectable or at background values within 50-150 days following sludge addition. E.coli numbers in unamended soils were highly dynamic and fluctuated between 1and 6 log10 100 g-1 ds during all field trials.
Clostridium and Campylobacter did not decay to a significant extent when introduced to both soils with sludge.
Sludge application consistently increased protozoa numbers in field soil, with raw sludge having a larger effect than anaerobically digested sludge, presumably due to greater availability of substrates in the unstabilised sludge. Protozoa numbers in biosolids-amended soils remained between 0.5 and 1 log above those of the control in field soil.
A laboratory incubation study provided evidence for the direct effect of soil protozoa activty and other ecological processes on E.coli decay in sludge-amended soil.

Price: £15  

Pathogens in Biosolids - Microbiological Risk Assessment

Reference: 03/SL/06/7
ISBN: 1-84057-294-9
Published Date: 24/06/2003

Biosolids represent the solid fraction of sewage and potentially contain a number of human and animal pathogens. This report describes a microbiological risk assessment to quantify the risks to humans from consumption of root crops grown on land to which treated biosolids have been applied in accordance with the Safe Sludge Matrix and the Regulations. The seven pathogens studied were Escherichia coli O157, Cryptosporidium, Giardia, Salmonella, Campylobacter, Listeria monocytogenes and enteroviruses. A number of worst-case assumptions have been made to accommodate lack of data. The predicted risks to the UK population as a whole are remote. Indeed, the highest risk is for Cryptosporidium with one infection in the UK population every 45 years on average. The model shows that the 12 month harvest interval compensates for any increased risks due to inefficient operation of sludge treatment at the works.

Price: £29  

Pathogens in Biosolids - The Fate of Pathogens in Sewage Treatment

Reference: 02/SL/06/6
ISBN: 1-84507 2612
Published Date: 30/04/2002

This study has evaluated the survival of a number of enteric pathogens added to thickened sewage sludge which was subjected to treatment by a range of processes operated under Code of Practice* conditions. These processes were: mesophilic anaerobic digestion (MAD), pasteurisation followed by MAD, lime stabilisation and composting. The experiments were carried out at bench-scale with additions of Salmonella senftenberg, S. dublin, S. enteriditis, S. typhimurium, Listeria monocytogenes, Campylobacter jejuni, Cryptosporidium parvum and poliovirus with the aim of achieving 106 organisms in the sludge. In addition the numbers of indigenous Escherichia coli were determined, not only in the bench-scale reactors but also at nominated full-scale plants that were operated under Code of Practice conditions; thermal drying was evaluated at full-scale only. Indigenous E. coli were shown to have similar survival properties to the verotoxigenic strain of E. coli O157 and could act as an indicator for this pathogen.

Price: £27