Recent Update on UV Disinfection to Fulfill the Disinfection Credit Value for Enteric Viruses in Water.

Ultraviolet (UV) radiation alone or in combination with other oxidation processes is increasingly being considered for water disinfection because of stringent regulatory requirements for pathogen inactivation. To fulfill this requirement, an appropriate UV dose or fluence (mJ/cm2) is applied to combat enteric viruses in surface or treated water. There is a need for a cumulative review on the effectiveness of current and emerging UV technologies against various types of human enteric viruses. We extracted the kinetics data from 52 selected experimental studies on enteric virus inactivation using low pressure (LP-UV), medium pressure (MP-UV), UV-LED, and advanced oxidation processes (AOPs) and applied a simple linear regression analysis to calculate the range of UV fluence (mJ/cm2) needed for 4-log10 inactivation. The inactivation of adenoviruses with LP-UV, MP-UV, and UV/H2O2 (10 mg/L) required the highest fluence, which ranged from 159 to 337, 45, and 115 mJ/cm2, respectively. By contrast, when using LP-UV, the inactivation of other enteric viruses, such as the Caliciviridae and Picornaviridae family and rotavirus, required fluence that ranged from 19 to 69, 18 to 43, and 38 mJ/cm2, respectively. ssRNA viruses exhibit higher sensitivity to UV radiation than dsRNA and DNA viruses. In general, as an upgrade to LP-UV, MP-UV is a more promising strategy for eliminating enteric viruses compared to AOP involving LP-UV with added H2O2 or TiO2. The UV-LED technology showed potential because a lower UV fluence (at 260 and/or 280 nm wavelength) was required for 4-log10 inactivation compared to that of LP-UV for most strains examined in this critical review. However, more studies evaluating the inactivation of enteric viruses by means of UV-LEDs and UV-AOP are needed to ascertain these observations.

The use of UV/H2O2 to facilitate removal of emerging contaminants in anaerobic membrane bioreactor effluents.

Effluent from anaerobic membrane bioreactor (AnMBR) contains ammonia and would require post-polishing treatment before it can be disinfected by chlorine. However, additional post-treatment steps to remove nutrients offset the energetic benefits derived from anaerobic fermentation. The use of chlorine or ozone also promotes concerns associated with disinfection byproducts. This study evaluates UV/H2O2 as a potential strategy suited for the removal of pharmaceutical compounds as well as antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) from AnMBR effluent. Our findings indicate that 10 mg/L H2O2 and 61.5 mJ/cm2 of UV fluence are able to achieve a 4-log removal of both Escherichia coli PI7 and Klebsiella pneumoniae L7. However, a higher fluence of 311 mJ/cm2 with the same amount of H2O2 would be required to achieve >90% removal of atenolol, carbamazepine and estrone. The removal of the pharmaceutical compounds was driven by the hydroxyl radicals generated from H2O2, while UV exposure governed the inactivation of ARB and ARGs. UV/H2O2 increased overall mutagenicity of the treated wastewater matrix but did not result in any changes to the natural transformation rates. Instead, UV significantly reduced natural transformation rates by means of DNA damage. Overall, UV/H2O2 could be the ideal final disinfection strategy for AnMBR effluent without requiring additional post-treatment prior disinfection.

Acquisition of Extracellular DNA by Acinetobacter baylyi ADP1 in Response to Solar and UV-C254nm Disinfection.

Extracellular DNA (eDNA) cannot be effectively removed by most of the existing wastewater treatment technologies and can contribute to the gain of new functional traits when transformed into competent bacteria present in downstream environments. This study evaluates the contributions of solar and UV-C254nm irradiation to the transformation of eDNA in Acinetobacter baylyi ADP1. Solar irradiation was evaluated because it is a natural environmental stressor to which eDNA would be exposed during wastewater reuse. UV-C254nm was evaluated as an alternative to a chlorine-based disinfection strategy. Our findings showed that solar disinfection increased the natural transformation frequency by up to 2.0-fold after irradiance at 153 mJ/cm2. This was largely mediated by reactive oxygen species generation, which was correlated with an upregulation of both DNA repair (recA and ddrR) and competence (comA and pilX) genes. In contrast, even though UV-C254nm exposure was accompanied by the upregulation of DNA repair (recA, ddrR, and uvrB) genes and, hence, possibly higher integration rates of eDNA, we observed a concentration-dependent decrease in transformation rates. This decrease in transformation was likely due to the UV dimerization of eDNA, which resulted in the integration of damaged genes that cannot be transcribed into any functional gene products. These results imply that even though sunlight stimulates eDNA uptake and integration in the natural environment, UV disinfection implemented at a treatment plant can potentially minimize subsequent detrimental effects by damaging the extracellular genetic material and ensuring that there is no substantial expression of these transformed genes.

Elucidating the Role of Virulence Traits in the Survival of Pathogenic E. coli PI-7 Following Disinfection.

Reuse and discharge of treated wastewater can result in dissemination of microorganisms into the environment. Deployment of disinfection strategies is typically proposed as a last stage remediation effort to further inactivate viable microorganisms. In this study, we hypothesize that virulence traits, including biofilm formation, motility, siderophore, and curli production along with the capability to internalize into mammalian cells play a role in survival against disinfectants. Pathogenic E. coli PI-7 strain was used as a model bacterium that was exposed to diverse disinfection strategies such as chlorination, UV and solar irradiation. To this end, we used a random transposon mutagenesis library screening approach to generate 14 mutants that exhibited varying levels of virulence traits. In these 14 isolated mutants, we observed that an increase in virulence traits such as biofilm formation, motility, curli production, and internalization capability, increased the inactivation half-lives of mutants compared to wild-type E. coli PI-7. In addition, oxidative stress response and EPS production contributed to lengthening the lag phase duration (defined as the time required for exposure to disinfectant prior to decay). However, traits related to siderophore production did not help with survival against the tested disinfection strategies. Taken together, the findings suggested that selected virulence traits facilitate survival of pathogenic E. coli PI-7, which in turn could account for the selective enrichment of pathogens over the non-pathogenic ones after wastewater treatment. Further, the study also reflected on the effectiveness of UV as a more viable disinfection strategy for inactivation of pathogens.