Animal by-products: Composting - Risk assessment
Use of composting to dispose of catering waste and animal by-products
Project Profile
In 2002, Defra commissioned a risk assessment 
(1 MB) to consider the health risks from the disposal of certain wastes by composting or treatment in a biogas plant. An outline of the risk assessment, carried out by WRc-NSF Ltd, is below.
At the time the risk assessment was commissioned, under the Animal By-Products Order 1999, as amended, all catering wastes, including source-separated material, which could contain or have been in contact with meat or other products of animal origin had to be disposed of so that livestock and wild birds could not gain access to them. Incineration and landfill were the primary disposal routes available. The objective of the study was to determine the risks to public and animal health from the land-spreading of the catering wastes after treatment by composting or in a biogas plant and to compare these with the risks from existing disposal routes.
The recommendations of the risk assessment were used to formulate the basis of our current UK national controls on the composting and anaerobic digestion of catering waste, set out in our domestic enforcement legislation, the Animal By-Products Regulations 2005.
What does the work cover?
Diseases
The project considers a wide range of human and animal pathogens, including:-
- Transmissible spongiform encephalopathies (TSEs) including BSE and scrapie;
- Exotic diseases such as Foot and Mouth Disease, Classical Swine Fever and Newcastle Disease; and
- Endemic diseases such as E. coli O157, campylobacters and Mycobacteria.
Impacts
The work investigates human exposures through the consumption of root crops grown on the land to which the composted wastes have been applied. Risks of transmission to livestock grazing on the land will be determined. The "knock-on effects" to humans of infected livestock will be considered. In this respect, a key consideration will be the impact, from economic, animal health and public health perspectives, of a single infection arising from exposure through land application of composted catering waste.
Types of composting
Data on the effectiveness of various biogas (anaerobic) and aerobic composting processes has been obtained for the purpose of the risk assessment. Of key importance in such a risk assessment is the control and operation of the composting processes. In particular "between-batch" and "within-batch" variations in the efficiency of pathogen destruction could markedly affect the overall risk. Collection methods are also taken into consideration.
Waste sources
Catering wastes (i.e. wastes from restaurants and domestic kitchens) of two types will be considered. These are the non-meat part of source-separated material and the un-separated material, which contains meat.
What questions does it answer?
The risk assessment addresses a number of questions, such as:
- What are the main agents of concern to human and animal health through land application of residues from composted catering wastes containing meat products?
- How effective are various composting processes in reducing any potential risks?
It also provides advice on the minimum standards that might be needed
to reduce the risks to an acceptable level.
The principal recommendations and conclusions of the risk assessment are
outlined in the Executive Summary
(74 KB).
The risk assessment will underpin advice on options and in particular
whether the UK should:-
- Maintain the current ban on the land application of compost and residues resulting from the use of composting and biogas treatments to dispose of animal by-products and catering wastes containing meat;
- Adopt new EC rules; or
- Adopt specific UK standards.
Catering waste will contain vegetable material and as such the disposal of composted waste on land may pose a risk to plant health. The Defra risk assessment on composting catering waste has considered the risks to plant health in principle but more detailed work needs to be done to assess the risk to crop production. Meanwhile, plant health risks should be managed by following existing guidance on composting as published in the former MAFF's Plant Health Code of Practice for the Management of Agricultural and Horticultural Waste (1998).
Page last modified: 17 July 2008