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Research Call

DAFM Reference


DAFM Award

DAFM National Call 2014 14/SF/847 Teagasc, (UCD, NUIG) €815,050

Project Title:

The comparative public and animal health risks associated with spreading Anaerobic Digestate, animal manure and slurry on land: Science, Policy and Practice

Project Coordinator:

Dr Declan J Bolton

Project Abstract

Anaerobic digestion of animal by-products (ABP), such as manure and slurry, produces digestate that ends up in the environment. A thorough investigation of anaerobic digestion processes is required to assess the risks to human and/or animal health associated with biological components in the original ABP and their AD products. In Ireland most AD biogas fermenters use manure and slurry as one of the primary raw materials but these may be supplemented with additional organic components such as food wastes to achieve the C:N ratio that is optimal for methane production. Manure, slurry and to a lesser extent food wastes may contain a range of hazards including animal pathogens and zoonotic agents (bacterial, viral and parasitic) which must be effectively inactivated during the process. Pathogen survival will be effected by initial concentration and AD conditions. Non-spore-forming bacteria, most viruses and some parasites can be inactivated by temperatures in the range of 50 to 100°C (Fayer 1994) but thermostable viruses and spore-forming bacteria require temperatures above 70 and 100°C, respectively. Many of these organisms are also sensitive to low and high pH, however some parasitic species, such as ascaris eggs, are tolerant to extreme pH values. On the basis of the temperatures and pH reached during processing, it would appear that the conditions during AD are not sufficient to ensure the destruction of bacterial, viral and parasitic pathogens. Biogas reactors in Ireland operate within different temperature ranges; mesophilic (between 35 and 40°C) and thermophilic (between 45 to 55°C) and pH values between 7 and 8.5 generally prevail (the pH should not decrease below pH 6.8 otherwise the metabolic activity of methanogenic bacteria is adversely affected and biogas production severely reduced). If these conditions of temperature and pH under anaerobic conditions are not sufficient to ensure pathogen destruction then the raw materials or digestate should be pasteurised, but again there is insufficient data to validate this pre/post AD thermal treatment. This project will investigate the survival of important human and animal bacterial, viral and parasitic pathogens during AD (with and without pre and/or post-AD pasteurisation), and examine the comparative risks to public and animal health associated with spreading digestate versus manure and/or slurry on land with an overall aim of providing the data/knowledge required to develop policy and practice that minimises the risks associated with anaerobic digestion.

Final Report:

Not available yet.