The Effects of UV Irradiation on the Biosorption of Titanium Dioxide Nanoparticles to Heterotrophic Biomass

The production of titanium dioxide (TiO2) nanoparticles has increased significantly in the past decades, which has generated concern due to their known toxicity in the environment. As a result of the production, use and disposal of productions containing TiO2, TiO2 nanoparticles are often received by wastewater treatment facilities. The adsorption of TiO2 nanoparticle to heterotrophic biomass has been previously studied; however, past studies did not address the effects of environmental transformations of the nanoparticles’ surface properties. These changes often occur in the environment prior to being received by the wastewater treatment facility. This study uses gold labeled TiO2 (Au@TiO2) nanoparticles to observe how exposure to ultraviolet (UV) irradiation modifies the surface properties of TiO2 nanoparticles, and ultimately affects their adsorption to heterotrophic biomass. Using instrumental neutron activation analysis, the limit of detection and the limit of quantification of Au@TiO2 nanoparticles in dried return activated sludge was found to be 5.49 mg/kg 7.02 mg/kg, respectively. These values are high due to the relatively large amount of background Au in the return activated sludge (24.0 µg/L). Exposure to UV irradiation reduced Au@TiO2 nanoparticle hydrophobicity and shifted the electrophoretic mobility versus pH curve to the left. Batch adsorption tests were used to quantify biosorption of Au@TiO2 nanoparticles to heterotrophic biomass. Analysis of Au in the supernatant and the settled solids from the batch adsorption tests yielded an incomplete material balance. The Au concentration of the supernatant suggested that exposure to UV irradiation increased biosorption to heterotrophic biomass. However, using the Au measured in settled solids, no relationship between exposure to UV irradiation and biosorption was observed. Further analysis is necessary to close the material balance and determine the effects of UV irradiation on biosorption