Pathogen Inactivation and Regrowth in Organic Waste during Biological Treatment

After proper sanitation treatment, organic wastes such as animal by-products, e.g. catering waste, slaughterhouse waste and manure can be used as fertilisers and soil conditioners and thereby contribute to a sustainable society. However, organic waste may contain pathogenic microorganisms and can thus present a health risk to both humans and animals if not properly treated. In the present thesis regrowth potential of Salmonella Typhimurium, Enterococcus spp. and coliforms in organic waste at psychrophilic and mesophilic temperatures and the time and temperature combinations required for pathogen inactivation during thermal treatments was investigated. This was done with the aim to contribute to hygienically safe recycling of organic waste. Pathogen growth was observed in active compost material as well as in fresh cattle manure. The growth potential decreased with increased maturity of the compost. In thermal treatment of fresh cattle manure, a treatment temperature of 52°C and a retention time of 17.2 h or a temperature of 55°C during 16.9 h were needed to achieve the reduction targets set by current EU regulation in terms of bacterial reduction. However, this time and temperature combination was not sufficient to achieve the reduction target of 3 log10 for parvovirus as a thermoresistant virus. The inactivation rate of Salmonella Senftenberg W775 and Enterococcus spp. were found to increase with increased moisture content whereas the opposite relationship between inactivation rate and moisture content was observed for viruses.