Open access publications in the SLU publication database

Abstract

Biowaste and sewage sludge can be used as a fertiliser and soil amendment in agriculture. However if not treated efficiently before use, such products can contain microbial pathogens that pose a health risk for humans and animals. This study investigated the pathogen content, mainly pathogenic and antimicrobial-resistant bacteria, present in sewage sludge and biowaste. It also assessed the effects of different treatment methods on various pathogens by analysis of the pathogen content of sewage sludge and biowaste substrate before and after treatment. Compared to sewage sludge, biowaste contained fewer pathogens, both in the untreated substrate and the digested residue. Frequent findings of Salmonella spp. in sewage sludge were the main reason for the difference. In addition, vancomycin resistant enterococci (VRE) were frequently isolated from sewage sludge. PFGE and PhenePlate analyses showed that both VRE and Salmonella spp. were capable of persisting for some months and up to two years, respectively, in the sewage sludge. Thus sewage sludge may act as a reservoir of Salmonella spp., VRE and other pathogens. Pasteurisation (70C, 60 minutes) proved to be an effective sanitation treatment for biowaste and in combination with anaerobic digestion it resulted in better inactivation of pathogens and indicator bacteria than the treatments currently used at Swedish wastewater treatment plants. In further studies at laboratory scale, pasteurisation effectively inactivated the majority of pathogens and indicator bacteria analysed except heat resistant (parvo-) viruses and spore-producing Clostridium perfringens. The pathogens and antimicrobial resistant bacteria found in sewage sludge and biowaste could be spread to humans and animals if these treated wastes are used in agriculture. However, it is possible to diminish the pathogen load in the wastes so that the risks to the community are minimised. It is important to be aware of the general hygiene risks associated with the biowaste and sewage sludge and to handle, treat and use these products accordingly.