Inactivation of Escherichia coli in Water by Combined Process of Silver Nanoparticle and Ultraviolet Radiation

Background: Now the goal of water disinfection is not just inactivation of pathogenic organisms, but other goals such reduction or minimization of disinfection by products (DBPs) formation, providing residue to control secondary infections, maintaining the disinfectant’s residue in the water distribution system to take care of public health are important too. Objectives: The current study aimed to study the effectiveness of new technologies such as combined process of silver nanoparticles (AgNPs) with ultraviolet (UV) radiation on Escherichia coli inactivation as a water microbial pollution index and effects of some parameters on its efficiency. Methods: AgNPs with average diameter of 20 nm was used in the presence or absence of UV light for disinfection. Escherichia coli species were cultured according to the standard methods for water and wastewater examination. The results were reported as CFU/mL. Results: Results showed that the disinfection efficiency of the UV light and silver nanoparticles (UV + AgNPs) combined process was more than that of the catalyst AgNP. The maximum efficiencies of the three processes of UV, AgNPs and UV + AgNPs in 60 minutes were 66%, 89% and 99%, respectively. The efficiency decreased with increasing the colony densities. However, statistical least significant difference (LSD) test showed no significant impact on the two consecutive levels (P > 0.05) . The removal efficiency increased with increasing the catalyst dose and contact time. The removal efficiency reached 100% when the catalyst dose was 0.4 mg/L at 20 minutes contact time. Conclusions: It was concluded that the efficiency of silver nanoparticles to remove E. coli increases under the UV light. Intensified disinfection practice was due to producing electrons, active holes and active radicals by irradiation of UV light on AgNPs.