Conceptual Model and Experimental Framework to Determine the Contributions of Direct and Indirect Photoreactions to the Solar Disinfection of MS2, phiX174, and Adenovirus

Abstract

Sunlight inactivates waterborne viruses via direct (absorption of sunlight by the virus) and indirect processes (adsorption of sunlight by external chromophores, which subsequently generate reactive species). While the mechanisms underlying these processes are understood, their relative importance remains unclear. This study establishes an experimental framework to determine the kinetic parameters associated with a virus' susceptibility to solar disinfection and proposes a model to estimate disinfection rates and to apportion the contributions of different inactivation processes. Quantum yields of direct inactivation were determined for three viruses (MS2, phiX174, and adenovirus), and second-order rate constants associated with indirect inactivation by four reactive species ((1)O2, OH(•), CO3(•-), and triplet states) were established. PhiX174 exhibited the greatest quantum yield (1.4 × 10(-2)), indicating that it is more susceptible to direct inactivation than MS2 (2.9 × 10(-3)) or adenovirus (2.5 × 10(-4)). Second-order rate constants ranged from 1.7 × 10(7) to 7.0 × 10(9) M(-1) s(-1) and followed the sequence MS2 > adenovirus > phiX174. A predictive model based on these parameters accurately estimated solar disinfection of MS2 and phiX174 in a natural water sample and approximated that of adenovirus within a factor of 6. Inactivation mostly occurred by direct processes, though indirect inactivation by (1)O2 also contributed to the disinfection of MS2 and adenovirus.

Solar Disinfection of Viruses in Polyethylene Terephthalate Bottles

“…Minor differences in structure and genetic composition are known to influence virus inactivation by different disinfectants (17,31). Here the observed susceptibility to RS was greatest for MS2, intermediate for EV, and lowest for HAdV and X174 (with approximately similar susceptibilities).…”

“…In the dark controls, only 2-log inactivation was observed after an equivalent exposure time. Previous work has shown that MS2 bacteriophages are readily inactivated by reactive species (17,18). Here, since PET bottles block most UVB radiation, we expect that MS2 inactivation is due strictly to indirect photoinactivation mediated by sensitizers present in the water.…”

“…Remarkably, HAdVs and MS2 have been shown to be similarly susceptible to RS (17). The negligible importance of photoinactivation to the overall HAdV inactivation was therefore unexpected.…”

Constructed Wetlands

“…Different pathogen types are also not necessarily removed at the same rate by a similar mechanism. For example, it was stated in the Waste Stabilization Pond chapter that viruses are generally more resistant than bacteria to removal from sunlight mediated reactions (Davies-Colley et al, 2005a;Sinton et al, 2002) and differences in their structural and genetic composition impacts the rate of removal (Silverman et al 2013;Mattle et al 2014;Kohn et al 2016).…”

Drinking Water Disinfection by Solar Radiation

“…Several modifications such as thermal enhancement, heterogeneous photocatalysis, chemical addition, flow reactors, solar mirrors have been developed to enhance the effectiveness of solar disinfection on pathogens especially viruses and protozoa which are very resistant to disinfection because of several limitations of traditional solar disinfection [20]. These systems are crucial in reducing the incidence of gastrointestinal infection in communities where supplying clean drinking water is limited or absent.…”