Hi all…a couple of quantitative microbial risk assessment (QMRA) articles with a Canadian focus have appeared on-line over the past few months, both having used the Health Canada QMRA model. The first, an article from our research Chair, has just appeared as an uncorrected proof in the Water Quality Research Journal of Canada. It is entitled “Scenario-based quantitative microbial risk assessment to evaluate the robustness of a drinking water treatment plant”, and demonstrates how to use the model to compare and assess the increase in risk due to potential treatment failures and unexpected variations in water quality and operating parameters of a water treatment plant.

The second, “Application of QMRA at 17 Canadian Water Treatment Facilities” appeared in the October 2015 issue of JAWWA. The authors found that “predicted risk estimates for the 17 WTPs revealed that only two did not comply with the 10-6 disability-adjusted life years (World Health Organization) and 10-4 risk of infection (US Environmental Protection Agency) reference levels because of the poor performance of direct filtration without coagulation.”

The abstracts of each are below.

 

Bill

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Scenario-based Quantitative Microbial Risk Assessment to Evaluate the Robustness of a Drinking Water Treatment Plant

Mohamed A. Hamouda, William B. Anderson, Michele I. Van Dyke, Ian P. Douglas, Stéphanie D. McFadyen, Peter M. Huck

Water Quality Research Journal of Canada-Available Online 18 February 2016, DOI: 10.2166/wqrjc.2016.034 

http://wqrjc.iwaponline.com/content/early/2016/02/18/wqrjc.2016.034

 

ABSTRACT

“While traditional application of quantitative microbial risk assessment (QMRA) models usually stops at analyzing the microbial risk under typical operating conditions, this paper proposes the use of scenario-based risk assessment to predict the impact of potential challenges on the expected risk. This study used a QMRA model developed by Health Canada to compare fourteen scenarios created to assess the increase in risk due to potential treatment failures and unexpected variations in water quality and operating parameters of a water treatment plant. Under regular operating conditions the annual risk of illness was found to be substantially lower than the acceptable limit. Scenario-based QMRA was shown to be useful in demonstrating which hypothetical treatment failures would be the most critical, resulting in an increased risk of illness. The analysis demonstrated that scenarios incorporating considerable failure in treatment processes resulted in risk levels surpassing the acceptable limit. This reiterates the importance of robust treatment processes and the multi-barrier approach voiced in drinking water safety studies. Knowing the probability of failure, and the risk involved, allows designers and operators to make effective plans for response to treatment failures and/or recovery actions involving potential exposures. This ensures the appropriate allocation of financial and human resources.”

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Application of QMRA at 17 Canadian Water Treatment Facilities

Tfaily, Randa; Papineau, Isabelle; Andrews, Robert C.; Barbeau, Benoit

October 2015 | Volume 107, Number 10 | Page(s) E497-E508

http://www.awwa.org/publications/journal-awwa/abstract/articleid/53621113.aspx

 

ABSTRACT

“A quantitative microbial risk assessment model developed by Health Canada was applied at 17 water treatment plants (WTPs) located throughout Ontario and Quebec, Canada. Four source water characterization methods were compared that considered Escherichia coli, Giardia, and Cryptosporidium. In addition, three strategies to evaluate chemical disinfection performances were compared (median disinfectant exposure [CT50], regulatory disinfectant exposure [CT10], and continuous-stirred tank reactors in-series [N-CSTR, where N is the number of CSTRs in the series]). The N-CSTR approach provides more reliable risk estimates because it is less sensitive to high inactivation conditions (when compared with use of CT10 or CT50). Predicted risk estimates for the 17 WTPs revealed that only two did not comply with the 10-6 disability-adjusted life years (World Health Organization) and 10-4 risk of infection (US Environmental Protection Agency) reference levels because of the poor performance of direct filtration without coagulation. This publically available quantitative microbial risk assessment model could help WTP managers assess overall treatment performance via a systematic evaluation process.”