Microbial risk assessment of sustainable urban stormwater management practices

Sustainable Urban Water Management (SUWM), a new approach to manage stormwater as a water resource instead of nuisance, has the potential to supplement the diminishing traditional water supplies as well as reducing surface water pollution from storm runoff. Uncertainties of public health risks represent one of the main barriers for the smooth transition to SUWM approach as urban stormwater is known to be highly variable in water quality and is less studied than the conventional water supplies. My research is aimed at improving our state-of-knowledge for the public health risks associated with the SUWM practices. Using the Quantitative Microbial Risk Assessment (QMRA) framework as my main research tool, I investigated the risk implications of three SUWM scenarios: 1) rainwater harvesting, 2) stormwater harvesting, and 3) discharging stormwater into recreational water. As household-level rainwater harvesting is the most readily implementable SUWM approach, I first investigated the public health risks associated with using the rooftop harvested rainwater for household produce irrigation—a reasonable scenario considering the relatively clean water quality of rainwater. My result showed that the risk associated with consuming produce irrigated by harvested rainwater exceeded the EPA’s benchmark for safe drinking water, but is still at least ten-fold lower than when reclaimed water is used for the same purpose. To investigate the risks associated with capturing, treating, and reusing urban stormwater collected from urban developments, I examined three non-potable household applications: 1) toilet-flushing, 2) showering, and 3) foodcrop irrigation. My results showed that harvested stormwater is only safe for toilet-flushing under the circumstances considered. However, interpretations of the risks also differ depending on the risk benchmark used for comparison. In my final case study, I adopted a new contamination source apportionment QMRA method to investigate the recreational health risks associated with discharging stormwater into a popular recreational beach. My results showed that sewage contamination of urban stormwater is the governing factor for elevated risks in the water. However, the risk levels are within the acceptable risk set by the U.S. EPA in most of the cases in spite of the violation of water quality standard due to contribution of fecal bacteria from non-human sources. The overall finding of my research demonstrated that the QMRA is a powerful tool to provide a scientific basis for SUWM decisions. The risk outcomes can be used to set the appropriate public health risk management guidelines and water legislation that are necessary for the progress of SUWM practices

Microbial risk assessment of sustainable urban stormwater management practices

Sustainable Urban Water Management (SUWM), a new approach to manage stormwater as a water resource instead of nuisance, has the potential to supplement the diminishing traditional water supplies as well as reducing surface water pollution from storm runoff. Uncertainties of public health risks represent one of the main barriers for the smooth transition to SUWM approach as urban stormwater is known to be highly variable in water quality and is less studied than the conventional water supplies. My research is aimed at improving our state-of-knowledge for the public health risks associated with the SUWM practices. Using the Quantitative Microbial Risk Assessment (QMRA) framework as my main research tool, I investigated the risk implications of three SUWM scenarios: 1) rainwater harvesting, 2) stormwater harvesting, and 3) discharging stormwater into recreational water. As household-level rainwater harvesting is the most readily implementable SUWM approach, I first investigated the public health risks associated with using the rooftop harvested rainwater for household produce irrigation—a reasonable scenario considering the relatively clean water quality of rainwater. My result showed that the risk associated with consuming produce irrigated by harvested rainwater exceeded the EPA’s benchmark for safe drinking water, but is still at least ten-fold lower than when reclaimed water is used for the same purpose. To investigate the risks associated with capturing, treating, and reusing urban stormwater collected from urban developments, I examined three non-potable household applications: 1) toilet-flushing, 2) showering, and 3) foodcrop irrigation. My results showed that harvested stormwater is only safe for toilet-flushing under the circumstances considered. However, interpretations of the risks also differ depending on the risk benchmark used for comparison. In my final case study, I adopted a new contamination source apportionment QMRA method to investigate the recreational health risks associated with discharging stormwater into a popular recreational beach. My results showed that sewage contamination of urban stormwater is the governing factor for elevated risks in the water. However, the risk levels are within the acceptable risk set by the U.S. EPA in most of the cases in spite of the violation of water quality standard due to contribution of fecal bacteria from non-human sources. The overall finding of my research demonstrated that the QMRA is a powerful tool to provide a scientific basis for SUWM decisions. The risk outcomes can be used to set the appropriate public health risk management guidelines and water legislation that are necessary for the progress of SUWM practices

Assessment of public health risk associated with viral contamination in harvested urban stormwater for domestic applications

Capturing stormwater is becoming a new standard for sustainable urban stormwater management, which can be used to supplement water supply portfolios in water-stressed cities. The key advantage of harvesting stormwater is to use low impact development (LID) systems for treatment to meet water quality requirement for non-potable uses. However, the lack of scientific studies to validate the safety of such practice has limited its adoption. Microbial hazards in stormwater, especially human viruses, represent the primary public health threat. Using adenovirus and norovirus as target pathogens, we investigated the viral health risk associated with a generic scenario of urban stormwater harvesting practice and its application for three non-potable uses: 1) toilet flushing, 2) showering, and 3) food-crop irrigation. The Quantitative Microbial Risk Assessment (QMRA) results showed that food-crop irrigation has the highest annual viral infection risk (median range: 6.8×10-4-9.7×10-1 per-person-per-year or pppy), followed by showering (3.6×10-7-4.3×10-2pppy), and toilet flushing (1.1×10-7-1.3×10-4pppy). Disease burden of each stormwater use was ranked in the same order as its viral infection risk: food-crop irrigation>showering>toilet flushing. The median and 95th percentile risk values of toilet-flushing using treated stormwater are below U.S. EPA annual risk benchmark of ≤10-4pppy, whereas the disease burdens of both toilet-flushing and showering are within the WHO recommended disease burdens of ≤10-6DALYspppy. However, the acceptability of showering risk interpreted based on the U.S. EPA and WHO benchmarks is in disagreement. These results confirm the safety of stormwater application in toilet flushing, but call for further research to fill the data gaps in risk modeling as well as risk benchmarks. © 2015 Elsevier B.V

Assessment of public health risk associated with viral contamination in harvested urban stormwater for domestic applications

Capturing stormwater is becoming a new standard for sustainable urban stormwater management, which can be used to supplement water supply portfolios in water-stressed cities. The key advantage of harvesting stormwater is to use low impact development (LID) systems for treatment to meet water quality requirement for non-potable uses. However, the lack of scientific studies to validate the safety of such practice has limited its adoption. Microbial hazards in stormwater, especially human viruses, represent the primary public health threat. Using adenovirus and norovirus as target pathogens, we investigated the viral health risk associated with a generic scenario of urban stormwater harvesting practice and its application for three non-potable uses: 1) toilet flushing, 2) showering, and 3) food-crop irrigation. The Quantitative Microbial Risk Assessment (QMRA) results showed that food-crop irrigation has the highest annual viral infection risk (median range: 6.8 × 10-4–9.7 × 10-1 per-person-per-year or pppy), followed by showering (3.6 × 10-7-4.3 × 10-2 pppy), and toilet flushing (1.1 × 10-7-1.3 × 10-4 pppy). Disease burden of each stormwater use was ranked in the same order as its viral infection risk: food-crop irrigation > showering > toilet flushing. The median and 95th percentile risk values of toilet-flushing using treated stormwater are below U.S. EPA annual risk benchmark of ≤ 10 showering > toilet flushing. The median and 95th percentile risk values of toilet-flushing using treated stormwater are below U.S. EPA annual risk benchmark of ≤ 10 toilet flushing. The median and 95th percentile risk values of toilet-flushing using treated stormwater are below U.S. EPA annual risk benchmark of ≤ 10-4 pppy, whereas the disease burdens of both toilet-flushing and showering are within the WHO recommended disease burdens of ≤ 10-6 DALYs pppy. However, the acceptability of showering risk interpreted based on the U.S. EPA and WHO benchmarks is in disagreement. These results confirm the safety of stormwater application in toilet flushing, but call for further research to fill the data gaps in risk modeling as well as risk benchmarks

Human and environmental health risks and benefits associated with urban stormwater

For stormwater harvesting to achieve its full potential in mitigating water scarcity problems and restoring stream health, it is necessary to evaluate the human and environmental health risks and benefits associated with it. Stormwater harbors large amounts of pollutants and has traditionally been viewed as a leading cause of water-quality degradation of receiving waters. Harvesting stormwater for household use raises questions of human exposure to pollutants, especially human pathogens, which have the potential to cause large-scale disease outbreaks. These issues are compounded by uncertainties relating to the performance of stormwater treatment technologies in pathogen removal. Quantitative microbial risk assessment provides an objective risk estimate based on scientific data and the best assumptions, which can be used to educate and instil confidence in stakeholders of the practice. Although limited, human health risk studies have positively supported the use of minimally treated rainwater and stormwater for some non-potable applications. In addition to the well-known benefit of preserving the stream hydrology and ecology, wetlands used for harvesting stormwater can also provide new habitats for wildlife that benefit environmental health. A fundamental change from viewing stormwater as waste to resource requires the coordinated efforts in research, education, and effective communication

Human and environmental health risks and benefits associated with use of urban stormwater

For stormwater harvesting to achieve its full potential in mitigating water scarcity problems and restoring stream health, it is necessary to evaluate the human and environmental health risks and benefits associated with it. Stormwater harbors large amounts of pollutants and has traditionally been viewed as a leading cause of water-quality degradation of receiving waters. Harvesting stormwater for household use raises questions of human exposure to pollutants, especially human pathogens, which have the potential to cause large-scale disease outbreaks. These issues are compounded by uncertainties relating to the performance of stormwater treatment technologies in pathogen removal. Quantitative microbial risk assessment provides an objective risk estimate based on scientific data and the best assumptions, which can be used to educate and instil confidence in stakeholders of the practice. Although limited, human health risk studies have positively supported the use of minimally treated rainwater and stormwater for some non-potable applications. In addition to the well-known benefit of preserving the stream hydrology and ecology, wetlands used for harvesting stormwater can also provide new habitats for wildlife that benefit environmental health. A fundamental change from viewing stormwater as waste to resource requires the coordinated efforts in research, education, and effective communication.</p

Assessment of public health risk associated with viral contamination in harvested urban stormwater for domestic applications

Capturing stormwater is becoming a new standard for sustainable urban stormwater management, which can be used to supplement water supply portfolios in water-stressed cities. The key advantage of harvesting stormwater is to use low impact development (LID) systems for treatment to meet water quality requirement for non-potable uses. However, the lack of scientific studies to validate the safety of such practice has limited its adoption. Microbial hazards in stormwater, especially human viruses, represent the primary public health threat. Using adenovirus and norovirus as target pathogens, we investigated the viral health risk associated with a generic scenario of urban stormwater harvesting practice and its application for three non-potable uses: 1) toilet flushing, 2) showering, and 3) food-crop irrigation. The Quantitative Microbial Risk Assessment (QMRA) results showed that food-crop irrigation has the highest annual viral infection risk (median range: 6.8×10-4-9.7×10-1 per-person-per-year or pppy), followed by showering (3.6×10-7-4.3×10-2pppy), and toilet flushing (1.1×10-7-1.3×10-4pppy). Disease burden of each stormwater use was ranked in the same order as its viral infection risk: food-crop irrigation>showering>toilet flushing. The median and 95th percentile risk values of toilet-flushing using treated stormwater are below U.S. EPA annual risk benchmark of ≤10-4pppy, whereas the disease burdens of both toilet-flushing and showering are within the WHO recommended disease burdens of ≤10-6DALYspppy. However, the acceptability of showering risk interpreted based on the U.S. EPA and WHO benchmarks is in disagreement. These results confirm the safety of stormwater application in toilet flushing, but call for further research to fill the data gaps in risk modeling as well as risk benchmarks. © 2015 Elsevier B.V