京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19983号 / 工博第4227号 / 新制||工||1654(附属図書館) / 33079 / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 伊藤 禎彦, 教授 米田 稔, 准教授 西村 文武 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24898号 / 工博第5178号 / 新制||工||1988(附属図書館) / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 伊藤 禎彦, 教授 松田 知成, 教授 越後 信哉 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

<p>To assess the performance of both treatment on reducing the infection risk, this study developed the Indoor Air Quality (IAQ) model that simulates the dynamics of airborne infective SARS-CoV-2 in a 500 m3 with or without mechanical ventilation and UV system. Then this model was linked to a quantitative microbial risk assessment (QMRA) to allow for estimation of the risk of disease transmission for a given treatment condition.</p>

The impact of climate change on drinking water is one of the fastest-growing challenges within the water sector. Microbial contamination of drinking water has been a serious issue for decades now and will exacerbate in the coming future. Until recently the impact of climate change was only evaluated qualitatively and there has been a growing need for a quantitative risk assessment. This review covers different ways of incorporating the effects of climate change into the risk assessment framework. A comprehensive search through two databases was conducted resulting in 596 citations being screened for relevance, of which 23 were confirmed as relevant. Ten risk assessment frameworks and 3 tools obtained from this review were used for the comparative study with the Swedish QMRA tool. Data from multiple frameworks and tools were extracted to identify potential additions required for the improvement of the Swedish tool. Two approaches, i.e. data-driven and process-based, were identified and the foundation for a new framework was set up. Two pathways to implement these approaches were laid out with the first being the addition of new modules to the existing tool and the second being the use of hydrodynamic and water quality models to predict the impact of climate change on infection risks.

It is now widely accepted that surface contamination plays an important role in the transmission of both respiratory and gastrointestinal infections in the domestic environment and community setting. The efficiency of transfer of a pathogen to the hand from a fomite is important in modeling transmission in microbial risk assessment models. The objective of this study was to use published literature to assess the role of fomites and hands in disease transmission, and to conduct fomite-to-finger transfer studies from various porous and nonporous fomites under different relative humidity condition using non-pathogenic strains of Escherichia coli, Staphylococcus aureus, MS2 coliphage, Bacillus thuringiensis spores, and poliovirus 1; to evaluate the persistence of bacteria and viruses on surfaces; to examine bacteria and virus transfer from treated surfaces; and to conduct a foodborne quantitative microbial risk assessment using Campylobacter jejuni from the data obtained in these studies. It was found that numerous factors influence the transfer efficiency of microorganisms, with moisture being the most important, with greater transfer under humid conditions. Other factors influencing transfer include drying time, contact time, pressure, friction, type of material, and porosity of the fomite. Percent transfer was greater under high relative humidity for both porous and nonporous surfaces. Most organisms on average had greater transfer under high relative humidity (40 - 65%) compared to low relative humidity (15 - 32%). Relative humidity and fomite type influenced the survival of all studied organisms; survival was greater on nonporous surfaces than those for porous surfaces. Test organisms were reduced up to 99.997% on the fomites after the surfaces were wiped with a disinfectant wipe. Microbial fomite-to-finger transfer from disinfectant wipe-treated surfaces were, lower than from non-treated surfaces. The disinfectant-wipe intervention reduced the risk of Campylobacter infection, illness, and death by 2 to 3 orders on all fomites. The disinfectant-wipe intervention reduced the annual risk of illness below the reported national average of diagnosed Campylobacteriosis cases 1.3E-04. This risk assessment demonstrates that the use of disinfectant wipes to decontaminate surface areas after chicken preparation reduces the risk of C. jejuni infections up to 99.2%.

Drinking water is produced from raw water and is either from groundwater or surface water. This thesis aims to find out if the cleaning process of raw water is sufficiently effective. This is important because consumers are otherwise at risk of waterborne infection caused by pathogens. There are three groups of pathogens; bacteria, virus and parasite. These have different characteristics which mean that they require different water treatment to be separated. In addition to normal operation, a number of scenarios were examined. This is to investigate how water treatment would do if they became a reality. The thesis has examined Borg´s waterworks operated by Norrköping Vatten AB. It was defined to cover the distance from water source to the consumer. In the work, the model Quantitative Microbial Risk Assessment (QMRA) was used to perform risk analysis by simulating the normal operation and different scenarios of the water purification process. Thus, knowledge can be obtained about the effectiveness of separation by bacteria, viruses and parasites. However, the QMRA-model is considered to contain some flaws and for that reason the Norwegian model called Good Disinfection Practice (GDP) was also used. GDP is a theoretical model which is based on formulas and tables. The model takes into account the raw water quality and also provides deductions for various measures that the water plant possesses to ensure a good supply of water. The results obtained with both models were similar and showed that the water treatment is sufficient for the bacteria, but not viruses and parasites. Both models were considered to be reliable but viruses and parasites are very difficult to analyze, which has resulted in uncertain literature values and hence in the results. The result also showed that neither viruses nor parasites exceeded the limit by so much that more hygienic barriers to the reduction of them are necessary. The conclusion which may be drawn from the fact that no parasites have been detected in the raw water is that the water treatment still might be sufficient. To determine the effects that an exclusion of various barriers may give, the normal operation was simulated and a purification step at a time was excluded. The result showed that the purification steps which are most important to maintain the treatment process are chemical precipitation followed by rapid filtration, slow filtration and disinfection with chlorine. If any of these cleaning steps were to fail, this introduces a large increase in the risk of waterborne disease. The results showed that the chemical precipitation step gave the greatest separation effect on the virus but also on the parasites. However, the slow filtration gave the largest separation of the parasites. Free chlorine had the greatest effect on bacteria. The investigated scenarios were assumed to be wastewater discharges, sewage discharges in relation to flood the nearby pastures, and sewage overflows due to heavy rainfall. The results of the simulated scenarios were the same when it was only bacteria that in all cases produced a result within the limits of the daily infection probability. Both viruses and parasites exceeded both values. However, there were few studies on these and thus literature values needed to be implemented in the QMRA-model. Hence, the uncertainty of the results was great. The QMRA-model also contained deficiencies in the simulation of the discharge of effluents, where the amount of virus was about 1000-10000 times too much. If this problem as well as more specific data for the investigated area, and more Swedish studies were available, a more credible simulation of the scenarios could be implemented.

The effectiveness of Boil Water Advisories (BWAs) as a public health risk management tool is increasingly being questioned. Newfoundland and Labrador's zero-risk policy for issuing BWAs on public drinking water systems has resulted in over 210 active BWAs annually, the majority classified as long-term BWAs. BWAs are more likely to occur on small systems, in communities with low economic capacity, and in communities without a certified operator. No relationship was found relating confirmed cases of water-related illness to BWAs. Quantifiable health risk associated with BWAs was evaluated using Quantitative Microbial Risk Assessment (QMRA). Data on source water pathogen concentrations and epidemiological data was used to evaluate and calibrate the QMRA Model. The study demonstrated the application of QMRA in determining whether health risk warranted issuing a BWA. Eleven recommendations were made on how the province could adopt QMRA in establishing an alternative drinking water risk management and advisory framework.

Less than 10% of the world’s domestic wastewater is disinfected prior to discharge into surface waters; therefore, human exposure to diverse wastewater-related pathogens results in millions of cases of illness each year. Among the enteric pathogens, viruses represent an important group of emerging pathogens and are frequently the cause of food- and water-borne outbreaks of illness. Although the World Health Organization and many government agencies mandate the use of bacterial indicators to identify poor microbial water quality, it is well known that these indicators poorly correlate with fecal pollution contamination events and risk of disease. The field of public health-related environmental microbiology has made significant advances over the last twenty years; however, there is still a need for improved methods to identify poor microbial water quality and manage health risks associated with water-related activities (e.g., recreation, shellfish harvesting, irrigation). Furthermore, it is imperative to effectively detect fecal pollution in the environment as well as determine the extent of pathogen removal during (waste)water treatment to meet the Sustainable Development Goals associated with water and food security as well as the water reuse recommendations by the U.S. National Research Council. This dissertation directly addressed the need to identify an improved viral indicator by exploring the application of pepper mild mottle virus (PMMoV), a virus of dietary origin that is extremely abundant in human feces, as a surrogate for enteric viruses in diverse settings and contexts. Using a reverse transcription quantitative polymerase chain reaction (RT-qPCR) method, PMMoV was compared with other indicators, index surrogates, and reference pathogens for assessing surface water quality in a developed country (Appendix A) and developing country context (Appendix B and C). In addition, the applicability of PMMoV as a (waste)water treatment process indicator was demonstrated in natural treatment systems in developing countries (Appendix C and D) and artificial treatment systems (Appendix E). In all settings, PMMoV always co-occurred with at least one reference pathogen, index organism, and/or indicator; additionally, PMMoV was detected more frequently and in higher concentrations than other reference pathogens and indicators. Three investigations also associated PMMoV detection with predicted human health risks greater than the health benchmark for recreation and water reuse activities (Appendix A, C, and D). Additionally, PMMoV facilitated an improved understanding of virus-particle interactions in wastewater treatment pond systems (Appendix D) and allowed for an improved understanding of virus removal with respect to riverbank filtration systems and wastewater reuse in agriculture (Appendix C). PMMoV was established as a valuable component of the microbial source tracking toolbox in Costa Rica (Appendix B) and appeared to be useful in Bolivia (Appendix C). Finally, a paradigm shift in (waste)water management is occurring, in which routine monitoring is being replaced by a more holistic approach that includes sanitary surveys, targeted water quality monitoring, and exploratory quantitative microbial risk assessment. To support and complement this paradigm shift, field-based, laboratory-free methods are needed to identify and/or infer the presence of enteric viruses (Appendix F). Collectively, all the investigations presented here confirm the use of PMMoV as a surrogate for enteric viruses; however, its utility depends on the context and research question.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19372号 / 工博第4117号 / 新制||工||1635(附属図書館) / 32386 / 新制||工||1635 / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 伊藤 禎彦, 教授 田中 宏明, 教授 米田 稔 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Yes / This paper presents a study to assess the roof-harvested rainwater (RHRW) in the Ikorodu area of Lagos state, Nigeria, and recommends guidance to minimise the health risk for its households. The types, design and use of rainwater harvesting systems have been evaluated in the study area to inspect the human risk of exposure to Escherichia coli (E. coli). To achieve these objectives, a detailed survey involving 125 households has been conducted which showed that 25% of them drink RHRW. Quantitative microbial risk assessment (QMRA) analysis has been used to quantify the risk of exposure to harmful E. coli from RHRW utilised as potable water, based on the ingestion of 2 L of rainwater per day per capita. Results have revealed that the maximum E. coli exposure risk from the consumption of RHRW, without application of any household water treatment technique (HHTTs) and with application of alum only, were 100 and 96 respectively, for the estimated number of infection risk per 10,000 exposed households per year. This estimation has been done based on 7% of E. coli as viable and harmful. Conclusively, it is necessary that a form of disinfectant be applied to the RHRW before use.