Bacteria and fungi inactivation by photocatalysis under UVA irradiation: liquid and gas phase

In the last decade, environmental risks associated with wastewater treatment plants (WWTPs) have become a concern in the scientific community due to the absence of specific legislation governing the occupational exposure limits (OEL) for microorganisms present in indoor air. Thus, it is necessary to develop techniques to effectively inactivate microorganisms present in the air of WWTPs facilities. In the present work, ultraviolet light A radiation was used as inactivation tool. The microbial population was not visibly reduced in the bioaerosol by ultraviolet light A (UVA) photolysis. The UVA photocatalytic process for the inactivation of microorganisms (bacteria and fungi, ATCC strains and isolates from indoor air samples of a WWTP) using titanium dioxide (TiO2 P25) and zinc oxide (ZnO) was tested in both liquid-phase and airborne conditions. In the slurry conditions at liquid phase, P25 showed a better performance in inactivation. For this reason, gas-phase assays were performed in a tubular photoreactor packed with cellulose acetate monolithic structures coated with P25. The survival rate of microorganisms under study decreased with the catalyst load and the UVA exposure time. Inactivation of fungi was slower than resistant bacteria, followed by Gram-positive bacteria and Gram-negative bacteria. [Figure not available: see fulltext.] © 2016, Springer-Verlag Berlin Heidelberg.

Financial support was partially provided by PTDC/EQU-EQU/100554/2008 (AIRPHOTOXI) and POCI-01-0145-FEDER-006984—Associate Laboratory LSRE-LCM funded by FEDER funds through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI)—and by national funds through FCT - Fundação para a Ciência e a Tecnologia. Caio Rodrigues-Silva acknowledges CAPES (2013:8674/13-2) and FAPESP (2014:2014/16622-3) research scholarship and the project CAPES/FCT 308/11 for the financial support. F.V.S. Lopes gratefully acknowledge FCT for his post-doc research fellowship, SFRH/BPD/73894/2010. V.J.P. Vilar and A.M.T. Silva acknowledge the FCT Investigator 2013 Programme (IF/00273/2013 and IF/01501/2013, respectively). This research was partially supported by the Strategic Funding UID/Multi/04423/2013 through national funds provided by FCT - Foundation for Science and Technology and European Regional Development Fund (ERDF), in the framework of the programme PT2020.