UV-A PHOTOCATALYTIC REMOVAL OF BIOAEROSOLS OVER TIO2-COATED GLASS RINGS

MARÍA LUCILA SATUF; SILVANA PIROLA; S. M. ZACARIAS; ORLANDO MARIO ALFANO

Praga

Congreso; 5th European Conference of Environmental Applications of Advanced Oxidation Processes; 2017

University of Chemistry and Technology, Prague, Czech Republic (UCT Prague)

UV-A PHOTOCATALYTIC REMOVAL OF BIOAEROSOLS OVER TIO2-COATED GLASS RINGSM. L. Satuf, S. Pirola, S. M. Zacarías, O.M. Alfano INTEC (Universidad Nacional del Litoral and CONICET), Predio CCT CONICET Santa Fe, Santa Fe, Argentina. mlsatuf@santafe-conicet.gov.arContinuous exposure to sporulated microorganisms represents serious health risks to human beings, including allergies and infection diseases, especially in confined environments. Heterogeneous photocatalysis with TiO2 is a potential alternative to mitigate the problem of biological air pollution. In the present work, the inactivation of Bacillus subtilis spores over TiO2-coated glass rings was evaluated under UV-A radiation. The coated rings represent a possible filling for photocatalytic reactors applied to indoor air purification.Borosilicate glass rings (5 mm × 10 mm) were coated with 1, 2 and 3 coatings of TiO2 P-25 (Evonik) by the ?dip-coating? technique. The thickness of the resulting TiO2 films was determined through SEM images. A suspension of B. subtilis spores was nebulized over the coated rings with a Collison 6-jet nebulizer (BGI Instruments), and then exposed to UV-A radiation (7.47 mW cm-2) for 7.5 hours. The nebulization of the spores simulates the real condition of bioaerosols in contact with a photocatalytic purification device. Bacterial inactivation was followed by analyzing the concentration of viable bacteria every 2.5 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 average thicknesses of the TiO2 films and the estimated values of the apparent inactivation constant (k), with the corresponding 95% confidence intervals. The orders of magnitude reduction in the concentration of viable spores after 7.5 h of irradiation is also reported in the table.Table 1. Film thicknesses, apparent inactivation constants, and orders of magnitude reductionTiO2 coatingsThickness (m)k (h-1)Orders of magnitude reduction 10.73  0.030.58  0.081.921.22  0.080.66  0.122.331.76  0.080.60  0.082.0When B. subtilis spores were irradiated over the coated rings, their viability decreased significantly and the inactivation extent increased with the irradiation time. Regarding the number of TiO2 coatings, maximum inactivation was reached with 2 coatings. Although the thickness of the TiO2 film increases with the number of coatings, a slight decrease in the apparent kinetic constant was obtained for 3 coatings. Possibly, under the conditions of these experiments, maximum production of hydroxyl radicals that are effective in the inactivation process is achieved in the film with 2 coatings. In thicker films, excessive production of hydroxyl radicals could lead to the formation of hydroperoxyl radicals, which are less effective for bacteria inactivation. Additionaly, an increase in the recombination of electrons and holes in the thicker film could contribute to the decrease in the inactivation rate [1]. Results have shown that glass rings with 2 coatings of TiO2 are a promising filling for air purification photocatalytic reactors.References[1]S. M. Zacarías et al. Ind. Eng. Chem. Res. 51 (2012) 13599.