Role of temperature and Suwannee river natural organic matter on inactivation kinetics of rotavirus and bacteriophage MS2 by solar irradiation

Indirect (UVA-visible spectrum) damage by exogenous sensitizers, indirect (UVB and UVA) damage by endogenous sensitizers, and direct UVB damage have been identified as three sunlight inactivation mechanisms for pathogens. This study investigated the role of temperature and Suwannee River natural organic matter (SRNOM) for each disinfection mechanism of rotavirus, an enteric virus, and MS2, a bacteriophage. For MS2 solutions irradiated at temperatures from 14-40??C, the inactivation rates followed the order: direct UVB damage > direct UVB damage in SRNOM solution > indirect UVA exogenous damage > indirect UVA endogenous damage. For rotavirus solutions irradiated at temperatures from 32-50??C, the inactivation rates (hr-1) were: direct UVB damage > direct UVB damage in SRNOM solution > indirect exogenous damage > indirect endogenous damage. Below 25??C, the indirect exogenous and endogenous damage were experimentally similar for rotavirus. Above 50??C, rotavirus inactivation was primarily due to heat damage. To further assess the rotavirus exogenous damage, quencher tests conducted at 50??C in the presence of 20 mg/L TOC demonstrate that H2O2 is important for rotavirus inactivation at high temperatures. However, other tests conducted with commercial H2O2 suggest that it is the role of H2O2 via the photo Fenton or Fenton-like pathways that is important, and that ???OH radicals are primarily responsible for rotavirus inactivation. Efforts to quench or inhibit ???OH radical formation with Na-formate and EDTA , respectively, in the presence of 20 mg/L TOC resulted in instantaneous damage to rotavirus. No other data were collected on the direct effects of ???OH radicals. While indirect UVA exogenous damage was significant for MS2 over 14-40??C, this mechanism should be considered for rotavirus over a higher range of temperature from 32 to 50??C. The observed difference in inactivation of MS2 and rotavirus suggested that it is crucial to investigate disinfection using enteric viruses