Airborne bacterial spores inactivation with UV radiation over TiO2 coated glass rings

ZACARIAS, SILVIA MERCEDES; MARÍA EUGENIA VISUARA; ORLANDO MARIO ALFANO; M. L. SATUF

Buenos Aires

Congreso; 5th International Symposium on Environmental Biotechnology and Engineering 2016 (5ISEBE); 2016

Instituto de Investigación e Ingeniería Ambiental (3iA), UNSAM

Bioaerosols containing viruses, bacteria, and fungi can be responsible for infectious diseases, toxic reactions, and allergic responses. Therefore, research on disinfection technologies to control bioaerosols in air constitutes an area of great scientific interest. Heterogeneous photocatalysis is a potential alternative to mitigate the problem of air contamination indoors, mainly to inactivate resistant forms of microorganisms such as bacterial spores. In this study, the photocatalytic inactivation of Bacillus subtilis (strain ATCC 6633) spores over TiO2-coated rings is evaluated. Borosilicate glass rings (5 mm diam × 10 mm length) were coated with 1, 2 and 3 layers of TiO2 P-25 (Evonik) by the ?dip-coating? technique. The coated rings were nebulized with a suspension of spores employing a 6 jet "Collison" type nebulizer (BGI Instruments), and then exposed to UV-A radiation for 12 hours. UV lamps of different irradiation power were employed in separate assays. Bacterial inactivation was followed by analyzing the concentration of viable bacteria every 2 hours. Experimental results were fitted with the exponential equation N=N0 exp(-kt), where N (CFU cm-2) is the concentration of viable bacteria per unit area of support, N0 (CFU cm-2) is the initial bacterial concentration, k (h-1) is the apparent kinetic inactivation constant, and t (h) is the irradiation time. CFU stands for colony forming units.Table 1 presents the values of the apparent kinetic constant k and the orders of magnitude reduction (OMR) of the initial concentration of viable bacteria (5x104 CFU cm-2) after 12 h of irradiation. It is worth noting that the spores? viability over glass rings without catalyst showed no changes in the presence of UV-A radiation. Significant reduction of the spores? viability was observed along the treatment, especially under the highest irradiation flux. It was also found that an increase in the number of TiO2 coatings enhances the inactivation rate. An increase in the UV-A irradiance or in the TiO2 content increases the absorption of energy by the catalyst and, therefore, the availability of reactive oxygen species able to damage the spores structure. Table 1. Inactivation constants under different experimental conditionsIncident radiation flux1.76 mW cm-27.47 mW cm-2TiO2 coatingsk [h-1]OMRk [h-1]OMR10,141 ± 0,0100,740,588 ± 0,0593,3120,177 ± 0,0210,970,677 ± 0,0323,3930,308 ± 0,0211,580,621 ± 0,0403,29Keywords: PHOTOCATALYSIS, INACTIVATION, BACTERIAL SPORES, TITANIUM DIOXIDE.