Airborne transmission of infectious diseases(SARS 2003 epidemic, COVID-19 pandemic, etc.,) has been a major concern in indoor spaces for many years. Photocatalytic treatment effectively reduces airborne microorganisms or bioaerosol(0.01-10µm) concentration in indoor spaces. Additionally, it can be retrofitted with the existing heating, ventilation, and air-conditioning(HVAC) systems. Photocatalytic inactivation of microorganisms is carried out majorly by the hydroxyl radicals(OH.) which have a high oxidation potential(2.730 ± 0.017 V) and, to a minor extent by the superoxide radicals(O2.-) . However, a lack of understanding of the complex interactions between bioaerosols on a photocatalyst(TiO2) coated filter irradiated by a light source inside an HVAC duct has hindered the furtherance of these systems. In this work, we intend to investigate the removal efficiency- reduction in viable concentration(PFU/m3)- of an aerosolized viral surrogate MS2 passing through a photocatalytic treatment section- UVC (254nm) + TiO2(Anatase, surface area ≥ 300 m2/g) coated filter(substrate)- installed to an HVAC wind tunnel. The removal efficiency of the aerosolized MS2 depends on the transport characteristics of the aerosolized microorganism, the intensity of the light reaching the photocatalyst substrate, and the intrinsic kinetics of the microorganism with the photocatalyst. Firstly, we evaluate the viable concentrations by collecting air samples from the duct through liquid impingers, and then further processing the collected samples through plaque assay analysis. Secondly, to measure the radiation characteristics of the system we use spherical actinometry with KI/KIO3 as the actinometer. Finally, we intend to investigate the inactivation rates of collected MS2 on two different substrates after exposing them to UV radiation for a specific period. The two substrates we will be using are a synthetic polyester fiber substrate, a typical HVAC filter material, and an aluminum honeycomb substrate. In addition to investigating the effects of the properties of the substrate, we will also be presenting the effects of different catalyst loadings on the inactivation rates.

Photocatalytic treatment of airborne microorganisms in HVAC systems

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