TiO₂ nanopowder and nanofilm catalysts in the disinfection and mineralization of S. aureus with solar-simulated radiation

Water contamination with various microorganisms is life threatening. TiO₂ semiconductor nanoparticles have been widely described for bacterial inactivation. However, such a process may yield hazardous organic matter in water; complete bacterial mineralization is thus imperative. This study describes how anatase TiO₂ nanopowder, suspended in water, photocatalyzes the inactivation and complete mineralization of Staphylococcus aureus using UV radiation from simulated solar radiation. Total organic carbon (TOC) analysis confirms bacterial photo-mineralization. Bacterial mineralization is further evidenced by the appearance of ammonium ions in the treated water. In the dark, and under visible light using a cut-off filter, only a small fraction of bacteria is inactivated with no mineralization. Nanofilm catalysts are also examined in batch reaction systems. The film catalyst exhibits a higher photocatalytic efficiency with a turnover frequency of up to ∼4.9 × 10⁸ CFU g⁻¹ min⁻¹ compared to ∼5.8 × 10⁶ CFU g⁻¹ min⁻¹ of the nanopowder film counterparts. The powder catalyst lost up to 65% of its efficiency on reuse. This is due to catalyst lost mass during recovery by filtration. The film catalyst retains about 96% of its efficiency upon second reuse, showing its feasibility in application. Moreover, the film catalyst is useful in a continuous flow reaction system with an efficiency of 5.4 × 10⁸ CFU g⁻¹ min⁻¹, which is higher than that in the batch system, and no measurable efficiency loss in reuse. These results open the door to use the present photodegradation process in large-scale water purification processes.