Transport Modeling in Sprinkler Irrigation

Treated wastewater (TWW) reuse in crop or landscape irrigation is beneficial for water resource preservation, both quantitatively and qualitatively. However, TWW reuse based on sprinkler irrigation remains limited. This is principally due to a poor understanding of the risks resulting from aerosolization and transport, particularly those associated with the inhalation of pathogenic or toxic contaminants during sprinkler irrigation. Pathogen dissemination is intrinsically linked to fine droplet dispersion and their transport over long distances. Such mechanisms have not been adequately addressed in sprinkler irrigation studies with regard to potential contamination of the environment or their impact on human health. In previous work, droplet dispersion was analyzed by conducting field measurements, and an empirical model was proposed. However, this model remained rather empirical and did not sufficiently take into account all the variables that are thought to act on evaporation. In this work, further measurements were made under a wider range of operating pressure and climatic conditions to improve the model. The set-up was improved by use of a new collecting device and methodology to avoid sampling pollution. Tracer concentration was increased, and the trial duration shortened to limit wind velocity variation effects on measurement accuracy. The objective was to model fine droplet volumes transported beyond the wetted perimeter of the sprinkler. This empirical modeling relies on climate variables and uses dimensionless numbers that characterize atomization and evaporation. Models that combine the key evaporation demand variables with Reynolds or Weber numbers better fit experimental data. They can account for more than 80% of transport variability, including very small volumes of water ($0.1\mathrm{mL}·{\mathrm{m}}^{-2}·{\mathrm{h}}^{-1}$) that are transported or deposited on the surface downwind from the wetted area.