A global sensitivity analysis of solar virus inactivation modeling

Waterborne pathogens related to the lack of safe drinking water and surface water contamination pose a substantial threat to human health. Sunlight-mediated inactivation of waterborne pathogens has been widely studied in natural surface waters, and it has been leveraged as a low-cost approach to disinfection for drinking water and wastewater treatment. Solar-driven disinfection systems can inactivate virus in water through two major mechanisms: direct endogenous mechanism causes damage to viral components (e.g. DNA/RNA, proteins) upon their absorption of sunlight photons (mostly UVB); indirect exogenous inactivation refers to the viral component damage caused by reactive intermediates, whose production is sensitized by external chromophores upon their absorption of sunlight photons (UVA and visible light). The solar virus inactivation process is affected by a wide range of factors, including sunlight irradiance, water absorbance, concentrations of photosensitizers, and water depth, among others. To elucidate the relative importance of environmental, water quality, photo-reactivity and engineering design parameters in solar virus inactivation in treatment systems, this study adapted and combined the aqueous photochemistry model, APEX, with the sunlight irradiance modeling program, SMARTS, to include different independent factors in a mathematical framework. The uncertainty of each parameter was characterized and incorporated into the Monte Carlo simulation of the integrated mechanistic model for three virus species (MS2 bacteriophage, phiX174 bacteriophage, and human adenovirus) and two water types (natural surface water, waste stabilization pond water), and a global sensitivity analysis was performed to quantitatively apportion the uncertainty of solar virus inactivation rate constant to different sources. This work demonstrated that environmental (location, diurnal and seasonal motion of the sun) and engineering design parameters (water depth) significantly outweigh water quality and photo-reactivity parameters in the determination of virus inactivation rate constants. System reliability and efficiency of a solar-driven disinfection system can be improved by optimizing its geometry configuration for sunlight exposure. Further Monte Carlo simulation of a 3D continuous stirred-tank reactor model coupled with the integrated solar virus inactivation model was performed to investigate the effect of different designs on the virus removal rate of a maturation pond system. Results showed that increasing the hydraulic retention time and the hydraulic efficiency are more cost-effective strategies than reducing pond depth for the improvement of virus removal. The analysis also revealed the trade-off between the solar virus removal performance and the diurnal fluctuation of effluent quality