Photocatalytic inactivation of viruses using titanium dioxide nanoparticles and low-pressure UV light

Abstract

The carcinogenic potential of chlorine disinfection by-products and recent changes in water quality regulations have led to a greater emphasis on alternative disinfection mechanisms. In this study, the efficacy of bench-scale and pilot-scale titanium dioxide (TiO₂) photocatalytic disinfection was explored using four bacteriophages (MS2, PRD1, phi-X174, and fr). The optimized bench-scale experiments indicated that 1 mg/L of Degussa P25 TiO₂ irradiated by low-pressure ultraviolet (UV) light reduced the dose requirements for viral inactivation in comparison to UV light alone. The highest UV dose reductions for 4-log inactivation of PRD1, MS2, phi-X174, and fr were 19%, 15%, 6%, and 0%, respectively. Bench-scale photocatalysis was inhibited by limited adsorption of the viruses onto the TiO₂ nanoparticles, as indicated by the poor results for high TiO₂ concentrations. Subsequently, pilot-scale experiments were completed using the Photo-Cat Lab from Purifics. The annular reactor configuration and increased viral adsorption dramatically improved photocatalytic inactivation for samples with high TiO₂ concentrations. Using the Photo-Cat Lab, 2-log inactivation of the bacteriophages was achieved with 400 mg/L of Degussa P25 TiO₂ and a UV dose of approximately 34 mJ/cm² (energy consumption of 0.33 kWh/m³)—a 700-fold decrease in energy use compared to bench-scale photocatalysis.

Keywords:

• Disinfection
• UV
• photocatalysis
• titanium dioxide
• PRD1
• MS2
• phi-X174
• fr

Acknowledgments

This research was supported by the National Science Foundation (NSF) Water Quality Center at Arizona State University. This work was performed while Daniel Gerrity was on appointment as a U. S. Department of Homeland Security (DHS) Fellow under the DHS Scholarship and Fellowship Program. All opinions expressed in this paper are the authors' and do not necessarily reflect the policies and views of NSF, DHS, or Purifics. The mention of product names does not constitute endorsement of the company.

Notes

^a Doses calculated using linear regression through triplicate points for four exposure times.

^b UV baseline denoted by a TiO₂ concentration of 0 mg/L.

^c UV inactivation did not vary for each bacteriophage due to changes in pH (data not shown).

^d Errors represent 95% confidence intervals.

^e Estimate based on single time point with triplicate plates (Fig. 3).

^a Hand et al.: 1 g/L Degussa P25 TiO₂, 1.8-L reactor volume, 450-W high-pressure mercury lamp, 0.91 W/L.^{[ 3 ]}

^b Cho et al.: 1 g/L Degussa P25 TiO₂, 50-mL reactor volume, 18-W black-light blue lamp, 7.9 × 10⁻⁶ einsteins/L-s.^{[ 6 ]}

^c Fig. 3: 1 g/L Degussa P25 TiO₂, 14-mL reactor volume, 15-W low-pressure mercury lamp, 0.13 mW/cm².

^d Fig. 4: 400 mg/L Degussa P25 TiO₂, 15-L reactor volume, 75-W low-pressure mercury lamp, 7 mW/cm².

^e Treatment goals: 70% destruction of THMFP and 4-log viral inactivation. In Hand et al., 70% destruction of THMFP would be necessary to comply with the Stage 2 D/DBPR.^{[ 3 ]}

^a Hypothetical surface density reported in residues/nm².

^b Level of inactivation based on data provided in Figure 4.