Safe Composting
15 July 2004
The study by risk analysis consultant Dr Paul Gale is published in this week's Veterinary Record. It should reassure farmers about the safety of Government plans to encourage wider use of composting as a means of disposing of organic waste.
Following the 2001 FMD outbreak, Defra banned the feeding of pigs with swill made from waste food from the catering industry. This left burial in landfill sites or incineration as the main options of disposing of material that could contain uncooked animal waste contaminated with a wide range of infectious agents. But there is growing environmental pressure to reduce dependence on landfill and there is invariably public opposition to building new incinerators.
Composting - using bacterial breakdown to generate the heat that will destroy most infectious agents - is an attractive alternative method for disposing of both commercial and domestic waste and creates a potentially valuable end-product. But Defra was concerned that livestock pathogens could survive the process and contaminate the soil on which the compost is used as fertiliser.
Dr Gale calculates the likely quantities of material contaminated with four diseases -foot and mouth, African swine fever, classical swine fever and BSE - that would enter composting plants each year and the rate of destruction during the process. He acknowledges that this is an inexact science but says he has erred on the side of caution in every case. Yet, he estimates that it would be unlikely that cattle or sheep would pick up enough virus when grazing to set off a foot-and-mouth epidemic - an event likely to occur only once every 200,000 years.
However, Dr Gale warns that the efficiency of composting in destroying infection depends on key parts of the operation, including separating out waste known to contain raw meat at the beginning and subjecting this high risk material to a two-stage composting process. Later, it is important that land fertilised with compost is left for two months before being used for grazing to allow any residual infectious agents to be dispersed and destroyed in the soil, he says.
Data from the study was used by Defra in drawing up rules on the technical specifications for operating composting plants set out in the Animal By-Products Regulations 2003.
Notes for Editors:
- For further information please contact Chrissie Nicholls or Helena Cotton in the BVA Press Office on 020 7636 6541 or email chrissien@bva.co.uk.