Removal of humic acid from aqueous solutions using ultraviolet irradiation coupled with hydrogen peroxide and zinc oxide nanoparticles

ABSTRACT

In this study, individual performance of ultraviolet irradiation (UV), zinc oxide nanoparticles (ZnO) and hydrogen peroxide (H₂O₂) processes, as well as a performance of combined processes of UV/H₂O₂ and UV/H₂O₂/ZnO, were assessed for the removal of humic acid (HA) from aqueous solutions. Various process-related factors, such as the concentration of ZnO (0.2 and 0.5 g/L), the concentration of H₂O₂ (20, 30 and 50 mg/L), UV = 125 W, pH (4, 7 and 10), initial HA concentrations (at wavelength of 254 nm) of 2, 5, 7 and 10 mg/L, and three types of interferences (nitrate, sulphate and chloride) were studied and optimised. The results showed that removal efficiency decreased by increasing the concentration of HA and pH values in all processes, but it increased by increasing the time of exposure and the concentration of H₂O₂. In the combined process of UV/ZnO/H₂O₂, the nanoparticle concentration of 0.2 g/L yielded the highest efficiency, whereas in the other processes, the highest efficiency was observed at nanoparticle concentration of 0.5 g/L. Based on these results, under the optimum conditions (HA = 2 mg/L, H₂O₂ = 50 mg/L, ZnO = 0.2 g/L, pH = 4.0 and contact time of 15 min), UV/ZnO/H₂O₂ process was found as the most efficient combination in removing of HA with an efficiency of 99.99%. Furthermore, the modelling results indicated that the adsorption reaction of HA onto ZnO nanoparticles was very well described by the pseudo-second-order kinetic model (R² > 0.99).

KEYWORDS:

• Ultraviolet irradiation
• zinc oxide nanoparticles
• hydrogen peroxide
• humic acid

Acknowledgments

This research has been supported by the Tehran University of Medical Sciences, School of Public Health, and Department of Environmental Health Engineering.

Disclosure statement

No potential conflict of interest was reported by the author(s).