Caracterización y tratamiento fotocatalítico de hongos y bacterias de aire interior

Abstract

Nowadays, people in developed countries spent most of their time in different indoor environments and the concern about indoor air quality has increased at the same time as the illnesses related with unhealthy buildings. Indoor Air Quality (IAQ) can be significantly deteriorated by high levels of bioaerosols that may cause infections, toxic reactions or allergies in building occupants. Indeed, there is no standard method for the quantification of this kind of pollution and several protocols and sampling devices are used. Consequently, there is an increasing demand for a systematic control of the indoor bioaerosols and efficient air purification systems. In this study, several methods for air sampling were tested such as gravitational settling on agar surfaces (sedimentation plates) or buffers (PBS), filtration or inertial impaction samplers. Moreover, three commonly used portable air samplers were compared: DUO SAS SUPER 360, SAMPL’AIR and SPIN AIR units and tested simultaneously for bacteria quantification in a laboratory room in realistic conditions. A fungal and bacterial characterization was done in buildings with different geographical location (Almería-Madrid-Soria), different age and at different seasons of the year. Bacterial and fungal samples were incubated and colony-forming units were counted. Polymerase Chain Reaction (PCR) technique (16S ARNr amplification) and subsequent sequenciation were used for bacterial species identification. For fungal identification microand macro-morphology examination of the colonies were used. Additionally, several samples isolated from Madrid building were identified by the amplification of the Internal Transcribed Spacer (ITS) region. Pathogenic bacteria, such as Pseudomonas aeruginosa, Escherichia coli and Francisella tularensis were isolated in most of the sampled buildings. Fungal identification results showed different species of Cladosporium, Alternaria, Penicillium, Aspergillus and an important number of yeasts in all the indoor environments sampled. These fungal genera can cause asthma, allergies or a contribution to the development of the Sick Building Syndrome (SBS). A new approach based on heterogeneous photocatalysis was tested to treat real indoor air. An annular UV-photocatalytic reactor was developed at laboratory scale where real indoor air was treated without recirculation. Results showed an efficient removal of airborne bacteria using TiO2 photocatalyst supported on transparent polymeric monoliths irradiated with UVA. As the laboratory scale photocatalytic tests were promising, a second photoreactor was designed, constructed and installed in an office. This demonstration scale photoreactor was attached to an HVAC system and was able to treat the indoor air by both photocatalysis or photolysis. For photocatalytic treatments aluminum monoliths were coated with a TiO2 sol-gel. The photoreactor was efficient to remove 97-99% of airborne bacteria when the catalyst was illuminated with three lamps during four hours and 81% of airborne fungi when nine lamps were lit inside the reactor. The experiments performed proved that this technology was efficient for bacteria and fungi removal and could compete with the dangerous conventional photolytic treatment with UVC.