Smittspridning via kompost och biogödsel från ... - Avfall Sverige

Summary
Large-scale activities for composting and biogas production are currently increasing in the
Nordic countries. In Sweden, the amount of organic waste that was treated by these processes
was in 2003 around 400 000 tonnes. This number may increase considerably in a few years,
partly as a result of the prohibition of putting organic waste on landfills that applies from the
turn of the year 2004-2005. Depending on the source of the waste, a wide spectrum of
disease-causing microorganisms may be present in the material that is to be treated within the
plants. This has lead to various restrictions and measures of safety, partly through legislation
on the national and international level, and partly through voluntary undertakings. Through
the system for certification, the Swedish National Testing and Research Institute (SP) today
administers a proper operation of the large-scale biogas plants, and the certification thereby
functions as a tool to manage the risks for, among other things, transmission of disease.
A large number of different infectious agents (pathogens) may potentially be present in
organic waste. Foodstuffs and raw materials may through inadequate hygienic handling be
contaminated, and it is calculated that a far greater number of food poisonings than what is
reported by the statistics occur in Sweden, which illustrates the presence of pathogens in food
waste. Smaller amounts of excreta from humans and animals may enter the plants via
household waste, and constitutes thereby a risk for disease transmission that need to be
considered. Animal manure is also present in the incoming material, and in the biogas plants
abattoir waste is also treated. Thereby may animal pathogens enter the plants, even if it is
counteracted by existing legislation. Garden waste that in itself is free of pathogens may be
contaminated by, for example, excreta from animals.
By composting and anaerobic digestion organic material is stabilised through decomposition,
whereby the volume decreases. The treatment processes also sanitise the organic material.
Proper temperature during a sufficient time period is considered to be of most importance for
the inactivation of infectious agents. In plants for anaerobic digestion of manure and abattoir
waste, pasteurisation at +70°C during 1 hour is demanded, which substantially reduces the
occurrence of pathogens. Even if pasteurisation precedes the main process, the final product
may be sensitive to reinfection and regrowth, which means that bacteria may grow in the
material from an initially low concentration. It is therefore of great importance that the
following handling, transport and possible storage is performed in a hygienically safe manner.
For composting, conditions for temperature and time are recommended by the Swedish EPA.
Covering of the compost decreases the risk for exposure to humans and animals, and will also
give a more even temperature and thereby a safer sanitisation. Composting in the thermophilic
temperature range (>50°C) normally gives a hygienically safe product.
Selection of incoming material, process requirements and restrictions for handling and use of
the products are measures that presently limits the risks for disease transmission through
legislation, regulations and voluntary undertakings. The intention is to keep the occurrence of
pathogens on a level where the use of compost and residues from digestion (bio-fertilizer) do
not result in an increase in disease cases in society. Naturally, something in the process may
malfunction and it is also possible that this is not discovered by the existing control system.
Therefore, it can not be excluded that pathogens may end up in the environment by the use of
compost and bio-fertilizer, but the probability of significant concentrations of pathogens being
present must be estimated to be low. In addition to sufficient control of the complete handling
chain, for example by the system for certification, it would be desirable that quality
parameters for compost and bio-fertilizer are further developed.
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