Disinfection of secondary treated sewage using chitosan beads coated with ZnO-Ag nanoparticles to facilitate reuse of treated water

BACKGROUND: Reuse of treated wastewater is necessary to augment supply of fresh water. Secondary effluent from a sewage treatment plant was disinfected using novel synthesized ZnO-Ag-chitosan beads under visible light. RESULTS: Final most probable number (MPN)/100 mL after 1 h contact time under direct sunlight was 920 with a loading of chitosan, Zn and Ag of 0.4 mg L-1 each. Disinfection resulted from the generation of reactive oxygen species. Disinfection efficiency reduced by 10% and 20%, when the total suspended solids (TSS) concentrations in the sewage were 50 mg L-1 and 100 mg L-1, respectively, compared with that with 30 mg L-1. A 5% and 10% reduction in disinfection efficiency was observed when sulphide concentration in sewage was increased from 10 mg L-1 to 20 mg L-1 and 50 mg L-1, respectively. Disinfection efficiency of the beads decreased by 10% when nitrate concentration in the sewage increased to 30 mg L-1 from zero. These novel beads had residual disinfection ability even after removal of beads from wastewater and these beads were successfully used for disinfection in four consecutive cycles. CONCLUSION: Successful disinfection of secondary sewage using chitosan beads coated with ZnO-Ag nanoparticles was established for the first time in this study to facilitate reuse of treated water. (C) 2017 Society of Chemical Industry