Photocatalytic treatment of bioaerosols: impact of the reactor design.

Comparing the UV-A photocatalytic treatment of bioaerosols contaminated with different airborne microorganisms such as L. pneumophila bacteria, T2 bacteriophage viruses and B. atrophaeus bacterial spores, pointed out a decontamination sensitivity following the bacteria > virus > bacterial spore ranking order, differing from that obtained for liquid-phase or surface UV-A photocatalytic disinfection. First-principles CFD investigation applied to a model annular photoreactor evidenced that larger the microorganism size, higher the hit probability with the photocatalytic surfaces. Applied to a commercial photocatalytic purifier case-study, the CFD calculations showed that the performances of the studied purifier could strongly benefit from rational reactor design engineering. The results obtained highlighted the required necessity to specifically investigate the removal of airborne microorganisms in terms of reactor design, and not to simply transpose the results obtained from studies performed toward chemical pollutants, especially for a successful commercial implementation of air decontamination photoreactors. This illustrated the importance of the aerodynamics in air decontamination, directly resulting from the microorganism morphology.

UV-A photocatalytic treatment of Legionella pneumophila bacteria contaminated airflows through three-dimensional solid foam structured photocatalytic reactors.

A 3D-structured photocatalytic media was designed for allowing a tubular reactor to work in a traversing-flow mode at low pressure drops with a strong increase in the surface area-to-volume ratio inside the reactor. A protective polysiloxane coating was performed for protecting a structured polyurethane foam and anchoring the active TiO(2) particles. Filled with the 3D-structured solid foam supporting TiO(2) photocatalyst, the reactor could thus take advantages from the static mixer effect and from the low pressure drop resulting from the reticulated foam support. Very efficient decontamination levels towards airborne Legionella pneumophila bacteria were reached in a single-pass test mode.

Numeration methods for targeting photoactive materials in the UV-A photocatalytic removal of microorganisms.

This tutorial review reports on the different numeration methods for evaluating the efficiency of the photocatalytic action on microorganisms. Here we put forward the advantages and drawbacks of the standard methods such as the plate count, the fluorescence techniques and the Most Probable Number method for determining the biocidal photocatalytic activity and thus selecting efficient photocatalytic materials among complex systems. We highlight that bacterial spores are a representative and suitable tool for meeting the restrictive requirements resulting from the complex use of living matter instead of chemical targets.