Karin Nyberg

Inactivation of bacteria and viruses in human urine depending on temperature and dilution rate.

Source separation and reuse of human urine can decrease the environmental pollution of recipient waters and reduce the need for artificial mineral fertilisers. However, the reuse of urine introduces another pathogen transmission route that needs to be managed. The inactivation of enteric pathogens and model organisms (Salmonella enterica subspecies 1 serovar Typhimurium (S. typhimurium), Enterococcus faecalis, bacteriophages S. typhimurium 28B, MS2 and Phi x 174) by urine storage was studied at dilutions (urine:water) 1:0, 1:1 and 1:3 at temperatures 4, 14, 24 and 34 degrees C. A threshold concentration of ammonia was found at approximately 40 mM NH(3) (e.g. 2.1 g NH(3)-NL(-1) and pH 8.9 at 24 degrees C), below which all studied organisms, except Salmonella, persisted considerably longer irrespective of treatment temperature, showing that urine dilution rate is of great importance for pathogen inactivation. For Salmonella spp. no threshold level was found in these studies (15 mM NH(3) lowest concentration studied). At temperatures below 20 degrees C, bacteriophage reduction was very slow. Therefore, urine stored at temperatures below 20 degrees C carries a high risk of containing viable viruses. The study indicated that the current recommended storage time for urine of 6 months at 20 degrees C or higher is safe for unrestricted use and could probably be shortened, especially for undiluted urine.

Inactivation of Ascaris Eggs in Source-Separated Urine and Feces by Ammonia at Ambient Temperatures

ABSTRACT Sustainable management of toilet waste must prevent disease transmission but allow reuse of plant nutrients. Inactivation of uterus-derived Ascaris suum eggs was studied in relation to ammonia in source-separated urine without additives and in human feces to which urea had been added, in order to evaluate ammonia-based sanitation for production of safe fertilizers from human excreta. Urine was used concentrated or diluted 1:1 and 1:3 with tap water at 4, 14, 24, and 34°C. Fecal material, with and without ash, was treated with 1% or 2% (wt/wt) urea at 24 and 34°C. At 34°C eggs were inactivated in less than 10 days in urine and in amended feces. At 24°C only feces with 2% (wt/wt) urea or 1% (wt/wt) urea at high pH (10) inactivated all eggs within 1 month, and no inactivation was observed after 75 days in urine diluted 1:3 (18 ± 11 mM NH3). At temperatures of ≥24°C, NH3 proved to be an efficient sanitizing agent in urine and feces at concentrations of ≥60 mM. Treating fecal material at 34°C can give a 6-log10 egg inactivation within 1 month, whereas at 24°C 6 months of treatment is necessary for the same level of egg inactivation. At temperatures of 14°C and below, inactivation rates were low, with viable eggs after 6 months even in concentrated urine.

Conversion of phenols during anaerobic digestion of organic solid waste – A review of important microorganisms and impact of temperature

During anaerobic digestion of organic waste, both energy-rich biogas and a nutrient-rich digestate are produced. The digestate can be used as a fertiliser in agricultural soils if the levels of hazardous compounds and pathogens are low. This article reviews the main findings about phenols in anaerobic digestion processes degrading organic solid wastes, and examines the effect of process temperature on the anaerobic degradation of phenols, the microbial community and the quality of the digestate. The degradation efficiency of a number of different phenols has been shown to be correlated to the process temperature. Higher degradation efficiency is observed at mesophilic process temperature than at thermophilic temperature. Possible explanations for this variation in the degradation of phenols include differences in diversity, particularly of the phenol-degrading bacteria, and/or the presence of temperature-sensitive enzymes. Chemical analysis of digestate from bioreactors operating at thermophilic temperature detected a higher content of phenols compared to mesophilic bioreactors, verifying the degradation results. Digestate with the highest phenol content has the greatest negative impact on soil microbial activity.

Quantitative Microbial Risk Assessment for Escherichia coli O157 on Lettuce, Based on Survival Data from Controlled Studies in a Climate Chamber

The aims of the study were to determine the survival of Escherichia coli O157 on lettuce as a function of temperature and light intensity, and to use that information in a screening-level quantitative microbial risk assessment (QMRA) in order to evaluate risk-reducing strategies including irrigation water quality guidelines, rinsing, and holding time between last irrigation and harvest. Iceberg lettuce was grown in a climate chamber and inoculated with E. coli O157. Bacterial numbers were determined with the standard plate count method after inoculation and 1, 2, 4, and 7 day(s) postinoculation. The experiments were carried out at 11, 18, and 25°C in light intensities of 0, 400, and 600 mmol (m(2))(-1) s(-1). There was a significant effect of temperature and light intensity on survival, with less bacteria isolated from lettuce incubated at 25 and 18°C compared with 11°C (P < 0.0001), and in light intensities of 400 and 600 mmol (m(2))(-1) s(-1) compared with 0 mmol (m(2))(-1) s(-1) (P < 0.001). The average log reductions after 1, 2, 4, and 7 day(s) were 1.14, 1.71, 2.04, and 3.0, respectively. The QMRA compared the relative risk with lettuce consumption from 20 scenarios. A stricter water quality guideline gave a mean fivefold risk reduction. Holding times of 1, 2, 4, and 7 day(s) reduced the risk 3, 8, 8, and 18 times, respectively, compared with harvest the same day as the last irrigation. Finally, rinsing lettuce for 15 s in cold tap water prior to consumption gave a sixfold risk reduction compared with eating unrinsed lettuce. Sensitivity analyses indicated that variation in bacterial inactivation had the most significant effect on the risk outcome. A QMRA determining the relative risks between scenarios reduces uncertainty and can provide risk managers with decision support.

Future threats to agricultural food production posed by environmental degradation, climate change, and animal and plant diseases - a risk analysis in three economic and climate settings

Global food security is one of the most pressing issues for humanity, and agricultural production is critical for achieving this. The existing analyses of specific threats to agricultural food production seldom bring out the contrasts associated with different levels of economic development and different climatic zones. We therefore investigated the same biophysical threats in three modelled types of countries with different economic and climatic conditions. The threats analysed were environmental degradation, climate change and diseases and pests of animals and plants. These threats were analysed with a methodology enabling the associated risks to be compared. The timeframe was 2012–2050 and the analysis was based on three underlying assumptions for 2050: the world population will have increased to 9 billion people, there will be a larger middle class in the world and climate change will be causing more extreme weather events, higher temperatures and altered precipitation. It is suggested that the risks, presented by the biophysical threats analysed, differ among the three modelled types of countries and that climate zone, public stewardship and economic strength are major determinants of these differences. These determinants are far from evenly spread among the world’s major food producers, which implies that diversification of risk monitoring and international assessment of agricultural production is critical for assuring global food security in 2050.

Treatment with Ca(OH)2 for inactivation of Salmonella Typhimurium and Enterococcus faecalis in soil contaminated with infected horse manure

Aim:  To investigate the inactivation of Salmonella enterica serovar Typhimurium and the faecal indicator Enterococcus faecalis in horse manure:soil mixtures by application of hydrated lime (Ca(OH)2).

Fate and survival of Salmonella Typhimurium and Escherichia coli O157:H7 in repacked soil lysimeters after application of cattle slurry and human urine

BACKGROUND Use of cattle slurry as a fertiliser is common practice around the world. Human urine use is not as common, but owing to its fertiliser value this might change in the future. It is essential to minimise the transfer of enteric pathogens through fertilisation, with respect to both animal and public health. Therefore the objective of this research was to study the survival and transport of Salmonella Typhimurium and Escherichia coli O157:H7 in two agricultural soils when applied to soil along with either cattle slurry or human urine over a period of 180 days. RESULTS Both Salmonella and E. coli O157:H7 were more rapidly reduced when applied together with human urine than when applied with cattle slurry. However, both pathogens persisted in low amounts at 20 and 50 cm depth in both soils throughout the whole study period. No Salmonella or E. coli O157:H7 was detected in the leachate over the 180 day study. CONCLUSION The risk of disease transmission is higher when cattle slurry is used as fertiliser compared with human urine. However, the risk of groundwater infiltration would be low as long as water velocity through the soil is moderate. Increased knowledge of pathogen persistence in soil after fertiliser application is a valuable tool for improving risk evaluations and formulating guidelines for the use of cattle and/or human wastes in cropping soils.

Biosecurity aspects and pathogen inactivation in acidified high risk animal by-products

The aim of the study was to investigate the effects of formic acid addition to ground high risk animal by-products (ABP 1) in terms of stabilization and pathogen inactivation and to evaluate the biosecurity risk connected with the ABP 1 based combustion fuel Biomal. Laboratory studies were performed on the persistence of Salmonella Typhimurium, Bacillus cereus spores, porcine herpes virus, avian influenza virus, bovine viral diarrhea virus, equine rhinitis A virus and porcine parvovirus in Biomal at different storage times. It was shown that Salmonella and enveloped viruses were inactivated within 1 day (24 h). Bacillus cereus spores were not reduced during 147 days and the non-enveloped virus porcine parvovirus was still detected after 168 days of storage. The conclusion that can be drawn from the study is that transmission of some highly contagious diseases such as foot-and-mouth-disease, swine vesicular disease and egg drop syndrome, caused by non-enveloped viruses, may follow accidental leakages of Biomal. In addition, there is a risk of transmission of the diseases anthrax and black leg, caused by sporulating bacteria.

Managing Salmonella Typhimurium and Escherichia coli O157:H7 in soil with hydrated lime – An outdoor study in lysimeters and field plots

An outbreak of Salmonella Typhimurium or E. coli O157:H7 among domestic animals can have great financial consequences for an animal enterprise but also be a threat for public health as there is a risk for transmission of the infection through the environment. In order to minimize disease transmission, it is important to treat not only the affected animals but also the areas on which they have been kept. In the present study, the effect of hydrated lime as a treatment for Salmonella Typhimurium or E. coli O157:H7 contaminated soil was investigated. The study was performed outdoors, in a lysimeter system and in field plots. The soils were spiked with Salmonella Typhimurium and/or E. coli O157:H7 and hydrated lime was added at three different concentrations (0.5, 1 and 2%). Sampling was performed over one month, and the levels of bacteria were analyzed by standard culture methods. In addition, the soil pH was monitored throughout the study. The results showed that application of 0.5–1 kg hydrated lime per m2 reduced both Salmonella Typhimurium and E. coli O157:H7 numbers to below the detection limit (2 log10 CFU g-1 soil) in 3–7 days. Lower application rates of hydrated lime did not reduce pathogen numbers in the lysimeter study, but in the field plots no E. coli O157:H7 was detected at the end of the four-week study period regardless of hydrated lime application. A recommended strategy for treating a Salmonella Typhimurium or E. coli O157:H7 contaminated soil could therefore be to monitor the pH over the time of treatment and to repeat hydrated lime application if a decrease in pH is observed.