1. Introduction, Danish Environmental Protection Agency

Development of a Nordic system for measuring the inactivation of pathogens during composting

1. Introduction

In 1999 the Nordic Council of Ministers initiated an investigation with the purpose to clarify how the sanitary aspects of composting garden, sludge and household waste can be described and controlled optimally under Nordic conditions (Christensen et al., 2000). In this investigation it was recommended to perform a full-scale investigation of the sanitary conditions at typically Nordic composting plants, to obtain results there can be used for optimising the present legislation’s and promote the sanitary safe use of compost. The described full-scale investigation includes microbiological analyses of the waste at different stages during the composting process (spot test analysis) as well as an indirect process supervision where physical and chemical parameters such as temperature, humidity and pH are registered. In addition, the inactivation of pathogens is investigated by means of a direct process evaluation. In this process, the raw material is inoculated in different points of the heap with selected pathogens in bags. After a sanitary composting phase (typically 2-4 weeks), the bags are collected and analysed for the survival of the inoculated pathogens. In Germany, this method is found suitable for the evaluation of pathogen reduction during the composting process.

In connection with the investigation performed for the Nordic Council of Ministers (Christensen et al., 2000), a hearing of Nordic experts was performed ensuring that the organisms included in the full-scale investigation are relevant for the Nordic environment. During this hearing, the experts suggested to inoculate with Escherichia coli and Streptococcus faecalis (indicator organisms for human and animal pathogens) and the plant pathogens Plasmodiophora brassicae, Rhizoctonia solani, Fusarium oxysporum and tobacco mosaic virus in the direct process evaluation. However, before the full-scale investigation is initiated, it is important that the analytic methods for the suggested indicator organisms are evaluated. In addition, control experiments are needed to evaluate the resistance of the chosen organisms under standard conditions for four weeks (the maximal duration of the sanitary phase). In Germany, experiences are available with the visual evaluation of biotests for tobacco mosaic virus and Plasmodiophora brassicae (Kehres & Pohle, 1998). However, the Nordic experts stressed that the survival of the inoculated plant pathogens also should be evaluated with a complementary microbiological technique (e.g. ELISA) when possible.

To ensure that the full-scale investigation can be initiated as soon as possible, The Danish Environmental Protection Agency therefore decided to support the present preparation study for the full-scale investigation in November 1999. The report is divided in two separate sections, one dealing with indicator organisms for human and animal pathogens and one dealing with plant pathogens. Each section ends up with recommendations for the full-scale investigation.