Infection risk assessment and safe contact distance determination for multi-nozzle water spray aerosols using a DPM-QMRA approach.

Reclaimed water is increasingly used in spray-based applications, including landscape fountains, urban greening, agricultural irrigation, and road cleaning, to alleviate urban water scarcity. However, these activities can generate pathogen-laden aerosols that pose potential health risks to exposed populations. This study developed an integrated quantitative framework for multi-nozzle spray scenarios to evaluate wind-dependent infection risks and determine differentiated safe contact distances. The discrete phase model (DPM) was used to simulate aerosol transport and spatial distribution, while Pseudomonas aeruginosa and Coxsackievirus were selected as representative bacterial and viral indicators. By coupling computational fluid dynamics (CFD) with quantitative microbial risk assessment (QMRA), inhalation exposure and associated infection risks were quantified under varying wind conditions. Results showed that aerosol concentrations and infection risks declined sharply within 10 m of the spray source, whereas higher wind speeds enhanced downwind transport and extended the exposure range. Sensitivity analysis identified pathogen concentration in reclaimed water as the most influential factor, followed by exposure frequency and exposure duration. Based on the U.S. EPA benchmark annual infection risk threshold of 10-4, recommended safe contact distances were >8 m upwind and >10 m downwind. This study provides a scientific basis for risk-informed design and management of reclaimed water spray systems.