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Application of a Dynamic Model to Assess Microbial Health Risks Associated with Beneficial Uses of Biosolids

Joseph Eisenberg
Joseph Eisenberg
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IWA Publishing
ISBN electronic:
Publication date:
January 2007

Microbial risk assessment is a structured approach to estimating risks associated with environmental exposure to pathogens by using available environmental data. In this report the researchers took advantage of three sources of environmental data to estimate risk: 1) pathogen monitoring of raw sludge efficacy of treatment processes, and pathogen monitoring of post-treatment biosolids. This risk assessment approach is able to estimate risks even for Class A biosolids where post-treatment monitoring data are all below the detectable level. Using this approach the researchers provide risk estimates for a number of different models to gain insight into risks associated with different aspects of the biosolids treatment and application process.

This report provides an approach to conducting risk assessments that takes advantage of pathogen data from raw sludge and data on treatment process efficacy as additional data sources to the post-treatment data. In this context the raw sludge and treatment data are considered prior information that can inform the risk estimate, and the post treatment data is used to inform the likelihood. A Bayesian structure like this one can be used to take full advantage of the available data into order to obtain the best risk estimate. As with any Bayesian analysis, if the data informing the likelihood is sparse, the posterior (or risk estimate) is strongly influenced by the prior. As the data improves, the posterior (or risk estimate) is influenced less by the prior. The reserachers provide risk estimates to illustrate how this can be used both in a regulatory context to make risk-based rules, and in a operation context to examine the benefits of changing treatment processes in the context of current application practices or proposed new practices.

Biosolids producers can use the results of this research to interpret the results and potential health implications of biosolids monitoring data. Treatment plant engineers can evaluate the potential risk-based benefits of making operational changes to existing treatment and/or adding additional treatment processes, and environmental managers can use this research to evaluate potential capitol improvements and/or land application site placement issues from a health-based perspective. Regulators at the U.S. EPA can use this framework to develop risk-based regulations parallel to the chemical contaminant rules. The risk assessment framework present in this report provides a mechanism to discuss biosolids management microbial risk using a common metric for comparison of treatment methods, management alternatives, and potentially to set risk-based standards for microbial contaminants in biosolids.

This title belongs to WERF Research Report Series

ISBN: 9781843397625 (Print)

ISBN: 9781780403892 (eBook)

Application of a Dynamic Model to Assess Microbial Health Risks Associated with Beneficial Uses of Biosolids
By: Joseph Eisenberg
ISBN (electronic): 9781780403892
Publisher: IWA Publishing
Published: 2007

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