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Thesis
A comparative risk metric of infection from exposure to pathogens in mesophilic anaerobic digested (MAD) class B biosolids
Master of Science (M.S.), Drexel University
May 2011
DOI:
https://doi.org/10.17918/etd-3727
Abstract
Treated sewage sludge, also commonly known as biosolids, has been widely used in landscaping and farming. Biosolids enhance the soil due to their high nutrient content and capacity to hold water. However, biosolids may also contain pathogens that can threaten public health. Digestion, lime stabilization, and composting are popular treatments used to reduce the pathogenic concentration. In the United States, land application of Class B biosolids "is a routine undertaking to reuse sewage sludge" (Sen et al, 2009). Class B biosolids are treated to reduce pathogens to low levels so that they pose minimal risk to public health and the environment. There are a wide variety of pathogens potentially present in biosolids, and the hazards presented by these pathogens vary based on their initial concentration, survival time, and dose response behavior. Thus, the objective of this project was to develop a comparative metric for the risk of infection from exposure to current concentrations of pathogens in mesophilic, anaerobic digested (MAD) Class B biosolids through the ingestion pathway. Various bacteria, viruses, and parasites were selected as pathogens of interest due to their risk of causing food and waterborne illnesses like gastroenteritis and infant diarrhea (Jones and Martin, 2003). Specifically, the aims of this research were to: (1) compile the most current and accurate data on the occurrence, dose-response, and decay parameters for as many pathogens as possible; (2) prioritize and classify pathogens as high, medium, or low risk; (3) fit distributional plots to the risk metric; and (4) determine which parameter contributed the most to the overall uncertainty. Results imply that special attention should be focused on Giardia, Adenovirus, Ascaris, Hepatitis A, and Rotavirus as they may present a high risk of infection if present in MAD Class B Biosolids. Ingestion of protozoa and viruses at infectious doses can lead to gastroenteritis, respiratory illness, heart disease, and paralysis (Metcalf and Eddy, 2003; Haas et al., 1999; and Straub et al., 1993). A number of statistical distributions were evaluated for their ability to fit the calculated values of the metrics for different pathogens. The Weibull model best fitted both the RRMO and RRM with ranges over seven and eight orders of magnitude, respectively. Results also showed that dose-response and decay parameters contributed the most uncertainty to the risk metrics developed here. Although occurrence was shown to not contribute as considerably as dose-response and decay, sufficient data to include occurrence in the assessment were available for only six pathogens.
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Details
- Title
- A comparative risk metric of infection from exposure to pathogens in mesophilic anaerobic digested (MAD) class B biosolids
- Creators
- Alrica Lincole Joe - DU
- Contributors
- Patrick L. Gurian (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Master of Science (M.S.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Resource Type
- Thesis
- Language
- English
- Academic Unit
- Civil (and Architectural) Engineering [Historical]; College of Engineering (1970-2026); Drexel University
- Other Identifier
- 3727; 991014632170004721