Direct potable reuse microbial risk assessment methodology: Sensitivity analysis and application to State log credit allocations

Abstract

Understanding pathogen risks is a critically important consideration in the design of water treatment, particularly for potable reuse projects. As an extension to our published microbial risk assessment methodology to estimate infection risks associated with Direct Potable Reuse (DPR) treatment train unit process combinations, herein, we (1) provide an updated compilation of pathogen density data in raw wastewater and dose-response models; (2) conduct a series of sensitivity analyses to consider potential risk implications using updated data; (3) evaluate the risks associated with log credit allocations in the United States; and (4) identify reference pathogen reductions needed to consistently meet currently applied benchmark risk levels. Sensitivity analyses illustrated changes in cumulative annual risks estimates, the significance of which depends on the pathogen group driving the risk for a given treatment train. For example, updates to norovirus (NoV) raw wastewater values and use of a NoV dose-response approach, capturing the full range of uncertainty, increased risks associated with one of the treatment trains evaluated, but not the other. Additionally, compared to traditional log-credit allocation approaches, our results indicate that the risk methodology provides more nuanced information about how consistently public health benchmarks are achieved. Our results indicate that viruses need to be reduced by 14 logs or more to consistently achieve currently applied benchmark levels of protection associated with DPR. The refined methodology, updated model inputs, and log credit allocation comparisons will be useful to regulators considering DPR projects and design engineers as they consider which unit treatment processes should be employed for particular projects.

Occurrence of coliphage in raw wastewater and in ambient water: A meta-analysis

“…This work summarizes coliphage density data in raw wastewater and in ambient waters. Distributions of indicators and pathogens based on a critical review of the literature add value to risk assessments (Soller et al 2017(Soller et al , 2018 and a greater understanding water and wastewater treatment needs (McMinn et al 2017, Pouillot et al 2015, Olivieri et al 2016. We applied a systematic literature search approach in identifying relevant literature.…”

“…Previously, a systematic review methodology was developed to evaluate densities of key viruses in raw wastewater and published distributions of norovirus densities in raw wastewater (Eftim et al 2017). These distributions are specifically useful for conducting quantiative microbial risk assessments (QMRA) (Soller et al 2018;Nappier et al 2018). For the derivation of coliphage-based recreational water quality criteria values, similar distributions of MSC and SC in raw wastewater and ambient waters are needed.…”

Health risks from protozoa in potable reuse: Implications of Florida's data set

“…The 20 facilities were geographically distributed throughout the state and represented a wide range of facility sizes, with typical flows ranging from a minimum of 0.9 mgd up to a maximum of 34 mgd and with a median facility flow of 5.5 mgd. The QMRA methodology for DPR described by Soller, Eftim, & Nappier, 2018 was adapted for this analysis. Simplifying assumptions included the consideration of risks from only one pathogen at a time (as site‐specific virus data were not available) and a simplified approach to DPR unit log‐reduction credits, which is discussed subsequently.…”

Antibiotic Resistance in Recreational Waters: State of the Science

“…Much of the research in the emerging field of environmental AMR has focused on wastewater as a source of AMR bacteria and ARGs to water. Untreated wastewater influent (or raw sewage) contains concentrated levels of pathogenic and nonpathogenic microbes [83,84] and antibiotics [85]. Wastewater and raw sewage can enter surface waters via combined sewer and sanitary sewer overflows [86,87].…”