Response of bioaerosol cells to photocatalytic inactivation with ZnO and TiO2 impregnated onto Perlite and Poraver carriers

Bioaerosols are airborne microorganisms that cause infectious sickness, respiratory and chronic health issues. They have become a latent threat, particularly in indoor environment. Photocatalysis is a promising process to inactivate completely bioaerosols from air. However, in systems treating a continuous air flow, catalysts can be partially lost in the gaseous effluent. To avoid such phenomenon, supporting materials can be used to fix catalysts. In the present work, four photocatalytic systems using Perlite or Poraver glass beads impregnated with ZnO or TiO2 were tested. The inactivation mechanism of bioaerosols and the cytotoxic effect of the catalysts to bioaerosols were studied. The plug flow photocatalytic reactor treated a bioaerosol flow of 460 x 1 0(6) cells/m(air)(3) with a residence time of 5.7 s. Flow Cytometry (FC) was used to quantify and characterize bioaerosols in terms of dead, injured and live cells. The most efficient system was ZnO/Perlite with 72% inactivation of bioaerosols, maintaining such inactivation during 7.5 h due to the higher water retention capacity of Perlite (2.8 mL/g(Perlite)) in comparison with Poraver (1.5 mL/g(Perlite)). However, a global balance showed that TiO2/Poraver system triggered the highest level of cytotoxicity to bioaerosols retained on the support after 96 h with 95% of dead cells. SEM and FC analyses showed that the mechanism of inactivation with ZnO was based on membrane damage, morphological cell changes and cell lysis; whereas only membrane damage and cell lysis were involved with TiO2. Overall, results highlighted that photocatalytic technologies can completely inactivate bioaerosols in indoor environments.

Automated summary

Bioaerosols, airborne microorganisms that can cause health issues, can be efficiently inactivated by photocatalytic technologies, with the ZnO/Perlite system showing the highest efficacy. Different mechanisms of inactivation were observed with ZnO and TiO2, highlighting the potential of photocatalysis in indoor environments.