Alyaa M. Zyara

This work is focused on the effects of kiwi zinc oxide (ZnO) nanoparticles that are prepared through green synthesis, on Staphylococcus aureus isolated from different cosmetic tools. Zinc acetate was utilized ions while kiwi peels extract was used as a reducing agent. The formation of zinc oxide nanoparticles (ZnO NPs) was confirmed by the change of the color from green to brown and the UV-visible spectral analysis which revealed a strong surface plasmon. In addition, transmission electron microscope, and Atomic Force Microscopy (AFM) characterization showed that ZnO NPs has a spherical shape with a mean diameter of 19.76 nm. Forty swab samples were taken from different cosmetics tools and were cultured. S. aureus was identified by the biochemical and molecular identification methods. Results showed powder sponge recorded the highest, among the cosmetic tools, that harbors staphylococci bacteria. The Minimum Inhibitory Concentration (MIC) with different concentrations (128, 64, 32 and 16) mg/ml of ZnO NPs, was studied. A well diffusion test was performed to detect S. aureus sensitivity towards Kiwi ZnO nanoparticles and the result showed that the lowest inhibition zone (of 17 mm) was produced by (16mg/ml) concentration and the greatest zone (of 27 mm) was recorded by (128mg/ml) concentration.

UV-LEDs are a new method of disinfecting drinking water. Some viruses are very resistant to UV and the efficiency of UV-LEDs to disinfect them needs to be studied. Drinking water was disinfected with UV-LEDs after spiking the water with MS2 and four UV- and/or Cl-resistant coliphages belonging to RNA or DNA coliphages isolated from municipal wastewater. UV-LEDs operating at a wavelength of 270 nm for 2 min with 120 mW of irradiation caused 0.93–2.73 Log₁₀-reductions of coliphages tested in a reactor of a 5.2 L volume. Irradiation time of 10 min in the same system increased the Log₁₀-reductions to 4.30–5.16. Traditional mercury UV (Hg-UV) lamp at a 254 nm wavelength caused 0.67–4.08 Log₁₀-reductions in 2 min and 4.56–7.21 Log₁₀-reductions in 10 min in 10 mL of water. All coliphages tested except MS2 achieved 4 Log₁₀-reductions with UV-LEDs at a dose that corresponded to 70 mWs/cm² using Hg-UV. Thus, UV-LEDs are a promising method of disinfecting UV- and/or Cl-resistant viruses.

Chlorine disinfection is a globally used method to ensure the safety of drinking water. However, it has not always been successful against viruses and, therefore, it is important to find new methods to disinfect water. Seventeen different coliphages were isolated from the treated municipal wastewater. These coliphages and MS2 were treated with different dosages of chlorine in drinking water, and a combined chlorine/ultraviolet irradiation treatment for the chlorine-resistant coliphages. Chlorine disinfection with 0.3 − 0.5 mg/L total chlorine (free Cl-dosage 0.12–0.21 mg/L) for 10 min achieved 2.5–5.7 Log₁₀-reductions for 11 sensitive coliphages. The six most resistant coliphages showed no reduction with these chlorine concentrations. MS2 was intermediate in chlorine resistance, and thus it is not a good indicator for viruses in chlorine disinfection. In the combined treatment total chlorine of 0.05–0.25 mg/L (free Cl-dosage 0.02–0.08 mg/L) and ultraviolet irradiation (14 − 22 mWs/cm²) were more effective than chlorine alone, and 3–5 Log₁₀-reductions were achieved for the chlorine-resistant strains. The chlorination efficiency could be increased by higher dosages and longer contact times, but this could increase the formation of disinfection by-products. Therefore, the combination treatment is a recommended disinfection method.

Ultraviolet (UV) irradiation is a common way to disinfect drinking water, but some viruses are very resistant to UV. Drinking water was disinfected with UV after spiking with MS2 and 18 different coliphages isolated from municipal wastewater effluent. In addition, some coliphages were disinfected with combined treatment of chlorine/UV or vice versa with UV/chlorine. A UV-dose of 22 mWs/cm² caused less than 2 Log₁₀-reductions of 10 UV-resistant strains, while it caused up to 7 Log₁₀-reductions for 9 UV-sensitive or intermediate strains. The high dose (117 mWs/cm²) caused only 3 Log₁₀-reductions in some UV-resistant coliphages, including MS2, which proved to be a good indicator for viruses in UV-disinfection tests. The combined treatment with 0.1 or 0.5 mg Cl/L (free Cl-dosage 0.04 or 0.2 mg/L, respectively) for 10 min followed by UV irradiation of 22 mWs/cm² inactivated all coliphages tested by >3.6 Log₁₀-units. Synergy was obtained for most coliphages tested by using a Cl/UV combination, and the inactivation using first low Cl-dosages followed by low UV-dosages was higher than if using high Cl- or UV-dosages alone. The opposite treatment with UV/Cl was less effective. Therefore, the combination treatment using first chlorine and then UV can be recommended as a disinfection method for viruses.