Evaluation of microbiological risks associated with direct potable reuse

This work evaluates the potential microbial risks associated with various direct potable reuse (DPR) treatment train combinations for recycled water. The assessment methodology leverages readily available peer-reviewed pathogen density and treatment process removal data and extends a previously published statistical approach. The results illustrate clear quantitative human health-based advantages for DPR projects in which product water is introduced into the raw water supply upstream of a conventional drinking water treatment facility, compared to those in which product water is introduced directly into a potable water supply distribution system. The results also indicate that a single day can drive annual risks, highlighting the need for robust and reliable on-line monitoring of unit treatment processes within DPR facilities. The methodology is adaptable to other DPR treatment trains and could be iteratively refined as additional data become available. This work will be useful to federal and state regulators considering DPR as source water, state and local decision makers as they consider whether to permit a particular DPR project, and design engineers as they consider which unit treatment processes should be employed for particular projects.