The UV Dose Used for Disinfection of Drinking Water in Sweden Inadequately Inactivates Enteric Virus with Double-Stranded Genomes

Effect of Human Adenovirus Type 35 Concentration on Its Inactivation and Sorption on Titanium Dioxide Nanoparticles

Removal of pathogenic viruses from water resources is critically important for sanitation and public health. Nanotechnology is a promising technology for virus inactivation. In this paper, the effects of titanium dioxide (TiO2) anatase nanoparticles (NPs) on human adenovirus type 35 (HAdV-35) removal under static and dynamic (with agitation) batch conditions were comprehensively studied. Batch experiments were performed at room temperature (25 °C) with and without ambient light using three different initial virus concentrations. The virus inactivation experimental data were satisfactorily fitted with a pseudo-first-order expression with a time-dependent rate coefficient. The experimental results demonstrated that HAdV-35 sorption onto TiO2 NPs was favored with agitation under both ambient light and dark conditions. However, no distinct relationships between virus initial concentration and removal efficiency could be established from the experimental data.

Fluorescence Spectroscopy for the Assessment of Microbial Load in UVC Treated Water

In this article, Fluorescence spectroscopy has been employed for the assessment of microbial load and it has been compared with the gold standard colony forming unit (CFU) and optical density (OD) methods. In order to develop a correlation between three characterization techniques, water samples of different microbial loads have been prepared by UVC disinfection method through an indigenously developed NUVWater sterilizer, which operates in close cycle flow configuration. A UV dose of 58.9 mJ/cm2 has been determined for 99.99% disinfection for a flow rate of 0.8 l/min. The water samples were excited at 270 nm which results in the tryptophan like fluorescence at 360 nm that decreases gradually with increase of UVC dose, indicating the bacterial degradation and it has been confirmed by OD and CFU methods. In addition, it has been proved that a close cycle water flow around UV lamp is imperative so that an appropriate dose must be delivered to microorganisms for an efficient disinfection. It has been found that due to the sensitive nature of Fluorescence spectroscopy, it yields immediate results, whereas, for CFU and OD methods, water samples needs to be inoculated for 24 h. Fluorescence spectroscopy, therefore, provide a fast, online, reliable and sensitive method for the monitoring of pathogenic quantification in drinking water.

The Virucidal Effect of the Chlorination of Water at the Initial Phase of Disinfection May Be Underestimated If Contact Time Calculations Are Used

For the microbiological safety of drinking water, disinfection methods are used to remove or inactivate microorganisms. Chlorine and chlorine dioxide are often used as disinfectants in drinking water treatment plants (DWTPs). We investigated the effectiveness of these chemicals in inactivate echovirus 30 (E30), simian 11 rotavirus (RV SA11), and human adenovirus type 2 (HAdV2) in purified water from a DWTP. Within two minutes of contact, chlorine dioxide inactivated E30 by 4-log10, RV SA11 by 3-log10, and HAdV2 could not be detected, while chlorine reduced E30 by 3-log10, RV SA11 by 2-3log10, and HAdV2 by 3-4log10. However, viral genomes could be detected for up to 2 h using qPCR. The CT method, based on a combination of disinfectant concentration and contact time, during such a short initial phase, is problematic. The high concentrations of disinfectant needed to neutralize organic matter may have a strong immediate effect on virus viability. This may lead to the underestimation of disinfection and overdosing of disinfectants in water with organic contamination. These results are useful for the selection of disinfection systems for reuse of treated wastewater and in the risk assessment of water treatment processes using chlorine and chlorine dioxide.

Inactivation and genome damage of rotavirus and a human norovirus surrogate by monochloramine treatment and sequential application with UV

The inactivation efficacy by monochloramine for disinfecting gastroenteritis-causing rotaviruses (RV) and Tulane viruses (TV), a surrogate for noroviruses, were evaluated in this study. In addition, the strategies for improving the disinfection efficiency of monochloramine by raising the temperature and sequentially implementing UV irradiation were investigated. The results showed that monochloramine was more effective in the inactivation of TV than RV. Additionally, the inactivation rate constants of RV and TV by monochloramine at 35 °C were improved approximately by 46% and 100%, respectively, compared to those at 25 °C. Moreover, applying UV irradiation before monochloramine enhanced the inactivation efficacy of RV and TV by 63% and 72% compared to monochloramine alone (UV: 6 mJ/cm², NH₂Cl: 60 ppm × min). Furthermore, the synergistic effect was observed during the RV inactivation by the sequential process. Especially, higher than 0.5 log₁₀ reductions of RV VP1 genome contributed to the synergistic effect in sequential treatment, while less than 0.1 log₁₀ reductions of RV VP1 genome were observed during UV alone (13 mJ/cm²) or monochloramine alone (94 ppm × min). The genome damage might be the primary mechanism of generating synergy in sequential treatment for the inactivation of RV. By comparison, no synergistic effect was discovered for the inactivation of TV due to high susceptibility to monochloramine and UV. The findings on the inactivation efficacy and mechanism for improvement will contribute to a wide application of monochloramine for virus inactivation in water treatment and distribution systems.