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.

Evaluating Microbial and Chemical Hazards in Commercial Struvite Recovered from Wastewater

“…Though the dry sample was not tested, postprecipitation processing steps will be integral for microbial reduction should spore-formers be considered an important class of AMR hazard. It has been previously shown that an accumulation of bacteria can occur during the filtration process of struvite production . The results of the study indicated that heating under moist conditions followed by desiccation would increase the inactivation efficiency .…”

“…The results of the study indicated that heating under moist conditions followed by desiccation would increase the inactivation efficiency . The drying temperature and moisture content were shown to play a role in the bacterial inactivation in which a low relative humidity allowed bacteria to persist, further indicating the importance of postprecipitation treatment steps …”

State of the art of urine treatment technologies: A critical review.

“… Decrey et al. (2011) and Bischel et al. (2016) investigated the inactivation of virus phages, helminth eggs ( Ascaris suum ), heterotrophic and total bacteria, as well as Enterococcus spp.…”

Controlled Synthesis of Struvite Nanowires in Synthetic Wastewater

“…Meanwhile, municipal wastewater contains a large amount of phosphorus, which can cause eutrophication when released into water bodies in excess. − To reconcile the simultaneous shortage and overabundance of phosphorus, struvite crystallization technique was developed. ,, Struvite, known as magnesium ammonium phosphate hexahydrate (MgNH 4 PO 4 ·6H 2 O), crystallizes in the orthorhombic system. , Due to its high phosphorus and nitrogen content and low solubility, struvite has been considered as an ideal slow-release fertilizer. ,,, In a specific reactor, struvite precipitation could be achieved by additional supplementation of Mg 2+ and NaOH into wasterwater, where Mg 2+ and pH all tend to be deficient for struvite precipitation. ,, In this way, phosphorus and nitrogen can be removed and recovered from wastewaters as reusable struvite. , In this regard, struvite crystallization technique can not only provide a means of phosphorus recovery, but also mitigate eutrophication of water bodies. Moreover, it is also reported that the deliberate struvite crystallization can help to solve scaling problems in wastewater treatment plants (WWTPs), and reduce sludge volumes. , Therefore, struvite precipitation has been regarded as a promising route to phosphorus recovery from wastewaters, and received increasing attention in recent years. ,,− …”

“…Moreover, it is also reported that the deliberate struvite crystallization can help to solve scaling problems in wastewater treatment plants (WWTPs), and reduce sludge volumes. 9,18 Therefore, struvite precipitation has been regarded as a promising route to phosphorus recovery from wastewaters, and received increasing attention in recent years. 3,10,19−24 However, the successful implementation of struvite precipitation in WWTPs depends on its economical sustainability.…”