Open access publications in the SLU publication database

Abstract

Land application of organic waste is a convenient disposal method, improves soil properties by adding organic matter and recycles plant nutrients. Used in this way, organic waste is a resource, but it can also be a transmission route for pathogens with animal and human origin, such as Salmonella, verotoxin-producing Escherichia coli (VTEC) and avian influenza virus (AIV).

Many pathogens are known to be able to survive for long time periods in soil after land application of organic waste. The total amount of pathogens entering the environment is eventually reduced due to environmental factors, e.g. UV-light and desiccation. Mitigation strategies applied after land application, for instance holding times, can reduce the risk for disease transmission to grazing animals. However, it is difficult to predict the reduction occurring within a given time. Thus, controlled mitigation strategies, such as, sanitization treatments are therefore needed.

This thesis investigated the effect of thermal treatment on the inactivation rate of bacterial and viral pathogens, aiming to produce a hygienically safe end-product. For thermal treatment of organic waste it is recommended to keep a temperature above 50°C. Some organisms, such as AIV, can be rapidly reduced at lower temperatures. However, many organisms show a slow reduction at lower temperatures and some bacterial pathogens, such as Salmonella, might even regrow. The reduction target of 5 log10, for Salmonella Senftenberg W775 and Enterococcus faecalis, can be reached within 11.7 h at a temperature of 50.5°C. To reach a 3 log10 reduction of the thermotolerant virus, in this case porcine parvovirus, sufficiently longer treatment times are needed, e.g. 42 h at 55°C. However, the use of such thermotolerant viruses in the validation process has been questioned. Making use of the less thermotolerant bacteriophage ΦX174, as a process indicator, indicates that the treatment recommendations concerning viral reduction could be lowered to 5.8 h at 55°C.

Thermal treatment can ensure; that a hygienically safe end-product is obtained from organic waste, safe handling of material from AI outbreaks, and help in reducing the risk for pathogen transmission to the environment.