Comparison of statistical evaluation approaches for log-removal validation according to European water reuse regulations

The Science of The Total Environment, vol. 964, pp. 178573

Abstract

-reduction values (LRV), it provides limited to no guidance on the necessary sample sizes and statistical evaluation approaches. The main requirement is that at least 90 % of the validation samples should meet the requirements. However, the interpretation of this 90 % validation target can significantly impact the required sample size, efforts necessary, and the risk of misclassifying WRTPs in practice. The present study compares different statistical evaluation approaches that might be considered applicable for LRV validation monitoring. Special emphasis is placed on the use of tolerance intervals, which combine percentile estimations with sample size-based uncertainty and confidence regions. Tolerance interval-based approaches are compared with alternative methods, including a) a binomial evaluation and b) the calculation of empirical percentiles. The latter are already used in existing European and U.S. regulations for bathing water and irrigation water quality. Our study demonstrates that using tolerance intervals allows for the reliable validation of WRTPs that achieve high LRVs relative to regulatory targets with comparatively smaller sample sizes compared to the other two approaches, while reducing the risk of misclassification. Additionally, we show that simplified approaches, such as a "9 out of 10" approach, pose a substantial risk of misclassification and should not be applied. We illustrate the behavior of these different approaches through simulation experiments and application to real data collected in 2022 and 2023 at a large WRTP in Germany.

Authors 4

1. Wolfgang Seis

   Delft University of Technology · Berlin Centre of Competence for Water

   Affiliation as printed

   Kompetenzzentrum Wasser Berlin gGmbH, Grunewaldstraße 60/61, 10825 Berlin, Germany; Department of Water Management, Faculty of Civil Engineering & Geosciences, Delft University of Technology, 2600 GA Delft, the Netherlands. Electronic address: wolfgang.seis@kompetenz-wasser.de

2. Michael Stapf

   Berlin Centre of Competence for Water

   Affiliation as printed

   Kompetenzzentrum Wasser Berlin gGmbH, Grunewaldstraße 60/61, 10825 Berlin, Germany

3. Ulf Miehe

   Berlin Centre of Competence for Water

   Affiliation as printed

   Kompetenzzentrum Wasser Berlin gGmbH, Grunewaldstraße 60/61, 10825 Berlin, Germany

4. Thomas Wintgens Aachen Institute of Environmental Engineering

   RWTH Aachen University

   Affiliation as printed

   Institute of Environmental Engineering, RWTH Aachen University, Mies-van-der-Rohe Strasse 1, 52066 Aachen, Germany