Inactivation of Aspergillus niger spores from indoor air by photocatalytic filters

The effects of UV-A and UV-C radiation on fungal spores were investigated before and after their germination in photocatalytic and non-photocatalytic air filters commonly used in heating, ventilating, and air conditioning (HVAC) systems.Immediately after the coating of spores on filters, exposure to both types of UV radiation induced the appearance of an inactivation threshold for long durations of exposure probably resulting from the presence of Aspergillus niger spores inside the activated charcoal layer. The use of a thin photocatalytic filter without activated charcoal demonstrated a better disinfection efficiency with total inactivation of the spores, due to an optimal contact between spores and TiO2 coating.The effects of UV radiation were then assessed on spore germination for both types of filters. The inactivation of spores in illuminated photocatalytic filters resulted in an irreversible inhibition of the fungal germination under UV-A or UV-C radiation. In contrast, fungal spores were able to germinate in non-photocatalytic filters despite previous exposure to both types of UV radiation. The monitoring of ergosterol amounts, the major sterol of fungal membranes, corroborated these results.Finally, UV-A or UV-C radiation exposure of filters after spore germination had a lesser disinfection efficiency than experiments whereby spores had just been applied onto the filters, due to the absence of contact between the biological pollutants and the photocatalyst coating.Our results thus demonstrated the interest to use photocatalytic filters ensuring optimal contact between pollutants and TiO2 coating to lead to a total inactivation of fungal spores in filters of HVAC systems.

Optical microscopy of the inside of a photocatalytic AC filter after the coating of fungal spores and 8 days of incubation in the dark at 25 °C and 98% RH.Figure optionsDownload as PowerPoint slideHighlights
► Effects of UV irradiated filters with or without TiO2 were studied on fungal spores.
► Total inactivation of spores in TiO2 filters without activated charcoal was observed.
► Ergosterol amount significantly decreased in TiO2 filters after UV exposure.
► Photocatalytic filters induced a durable inhibition of the spore germination.
► Contact between TiO2 and spores was a critical point for inactivation efficiency.