title: Bacteria Inactivation during the Drying of Struvite Fertilizers Produced from Stored Urine.
abstract: Human urine can be processed into market-attractive fertilizers like struvite; however, concerns regarding the microbial safety of such products remain. The present study evaluated the inactivation of in situ heterotrophs, total bacteria as observed by flow cytometry, and inoculated Enterococcus spp. and Salmonella typhimurium during the drying of struvite under controlled temperature (from 5 to 35 °C) and relative humidity (approximately 40 and 80%) as well as dynamic field conditions. Bacteria accumulated in the struvite cake during struvite filtration. Despite the use of sublethal temperatures, all bacteria types were subsequently inactivated to some degree during struvite drying, and the inactivation typically increased with increasing drying temperature for a given relative humidity. Heterotrophic bacteria inactivation mirrored the trend in total bacteria during struvite drying. A linear relationship was observed between inactivation and sample moisture content. However, bacteria survivor curves were typically nonlinear when struvite was dried at low relative humidity, indicating bacterial persistence. Weibull model survivor curve fits indicated that a shift in the mechanism of inactivation may occur with changing humidity. For increased efficiency of bacterial inactivation during the production of struvite, initial heating under moist conditions is recommended followed by desiccation.
authors.affiliation: Laboratory of Environmental Chemistry, School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.
authors.forename: Heather N
authors.initials: HN
authors.lastname: Bischel
authors.affiliation: Laboratory of Environmental Chemistry, School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.
authors.forename: Simon
authors.initials: S
authors.lastname: Schindelholz
authors.affiliation: Laboratory of Environmental Chemistry, School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.
authors.forename: Manfred
authors.initials: M
authors.lastname: Schoger
authors.affiliation: Laboratory of Environmental Chemistry, School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.
authors.forename: Loïc
authors.initials: L
authors.lastname: Decrey
authors.affiliation: Pollution Research Group, Faculty of Engineering, University of KwaZulu-Natal , Durban 4041, South Africa.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Buckley
authors.affiliation: Eawag: Swiss Federal Institute of Aquatic Science and Technology , 8600 Dübendorf, Switzerland.
authors.forename: Kai M
authors.initials: KM
authors.lastname: Udert
authors.affiliation: Laboratory of Environmental Chemistry, School of Architecture, Civil and Environmental Engineering (ENAC), École Polytechnique Fédérale de Lausanne (EPFL) , CH-1015 Lausanne, Switzerland.
authors.forename: Tamar
authors.initials: T
authors.lastname: Kohn
mesh_terms: D001419:Bacteria; D003890:Desiccation; D005308:Fertilizers; D006801:Humans; D006813:Humidity; D000069877:Struvite; D013696:Temperature
chemical_list: D005308:Fertilizers; D000069877:Struvite