Quantifying pathogen risks associated with potable reuse: A risk assessment case study for Cryptosporidium.

Area of Science:

• Environmental Engineering
• Water Reuse Technologies
• Risk Assessment

Background:

• Potable reuse is crucial for water security.
• Evaluating microbial risks in different reuse paradigms is essential for public health.
• Conventional and advanced treatment systems vary in their effectiveness.

Purpose of the Study:

• To compare the microbial risk of Cryptosporidium infection across three potable reuse systems: de facto, indirect potable reuse (IPR), and direct potable reuse (DPR).
• To assess the impact of optimal and sub-optimal operational conditions on risk.
• To identify critical parameters influencing risk in potable reuse.

Main Methods:

• Quantitative Microbial Risk Assessment (QMRA) was employed.
• Risk of infection from Cryptosporidium oocysts was quantified.
• Sensitivity analyses identified critical model and operational parameters.

Main Results:

• DPR demonstrated significantly lower annual infection risks (mean of 6.1 × 10⁻⁹) compared to de facto and planned IPR systems (mean of 9.4 × 10⁻⁵ to 4.5 × 10⁻⁴).
• For planned IPR, risks were often dictated by raw surface water pathogen loading, decreasing with higher recycled water contributions.
• Advanced treatment failures had minimal impact due to system robustness (DPR) or environmental buffer resilience (IPR).
• A critical environmental buffer storage time of approximately 105 days was identified for de facto reuse systems.

Conclusions:

• DPR systems provide superior microbial safety for potable water.
• The effectiveness of IPR relies heavily on the quality of the source water and adequate environmental buffer.
• Operational parameters like storage time are critical for ensuring safety in de facto reuse systems.
• Findings can inform regulatory decisions and design criteria for potable water reuse.