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

Abstract

•ZnO/Perlite inactivated 72% of bioaerosols in continuous gas phase.

•TiO₂ triggered the highest level of cytotoxicity with 95% dead cells onto Poraver.

•Inactivation mechanism occurred by membrane damage, morphological changes and lysis.

•ZnO/Poraver showed null inactivation of bioaerosols.

•Catalysts losses at the outlet of the photoreactor for all systems were negligible.

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 460×1 0⁶ cells/m³_air 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.

Graphical abstract

Keywords

Immobilized catalysts / Continuous flow / Photocatalysis / Bioaerosols / Cytotoxicity / Inactivation mechanism

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