Pol J Microbiol. 2013;62(2):131-9.

The effectiveness of photocatalytic ionisation disinfection of filter materials.

Pietrzak K, Gutarowska B.

Institute of Fermentation Technology and Microbiology, Łódź University of Technology, Poland. khpietrzak@gmail.com

 

Abstract

The purpose of this study was to determine the effectiveness of photocatalytic ionisation as a disinfection method for filter materials contaminated by microorganisms, and to assess how air relative humidity (RH), time and microbe type influence the effectiveness of this disinfection. In the quantitative analysis of a used car air filter, bacterial contamination equalled 1.2 x 10(5) cfu/cm2, fungal contamination was 3.8 x 10(6) cfu/cm2, and the isolated microorganisms were Aspergillus niger, Bacillus megaterium, Cladosporium herbarum, Cryptococcus laurenti, Micrococcus sp., Rhodotorula glutinis and Staphylococcus cohnii. In the model experiment, three isolates (C. herbarum, R. glutinis, S. cohnii) and 3 ATCC species (A. niger, E. coli, S. aureus) were used for photocatalytic ionisation disinfection. The conditions of effective photocatalytic ionisation disinfection (R > or = 99.9%) were established as 2-3 h at RH = 77% (bacteria) and 6-24 h at RH = 53% (fungi). RH has an influence on the effectiveness of the photocatalytic disinfection process; the highest effectiveness was obtained for bacteria at RH = 77%, with results 5% higher than for RH = 49%. The studies show that the sensitivity of microorganisms to photocatalytic ionisation disinfection is ordered as follows: Gram-positive bacteria (S. cohnii, S. aureus), Gram-negative bacteria (E. coli), yeasts (R. glutinis), and moulds (C. herbarum, A. niger). Of all the mathematical models used for the description of death dynamics after photocatalytic ionisation disinfection, the Chick-Watson model is the most useful, but for more resistant microorganisms, the delayed Chick-Watson model is highly recommended. It therefore seems, that the presented disinfection method of photocatalytic ionisation can be successfully used to clean filtration materials.

PMID: 24053016

 

SUPPLEMENT:

The problem of microbial contamination of car interiors is common. At present, people spend  more and more time in cars. The number of microorganisms in the air, in the form of bioaerosol, equals to 102-103 cfu/m3. The dangerous situation occurs, when this amount is higher than that in the outdoor air The best way to protect people is the cleaning and disinfection of the car interiors (AC system). One of these methods could be photocatalytic ionization disinfection.

The mechanism of the photocatalytic ionization process is the creation of reactive oxygen species (ROS) –superoxide radical (O2), hydroxyl (OH), (hydrogen peroxide) H2O2 and ozone (O3) on the semiconductor catalyst (TiO2) from the water vapour (H2O) and air (O2) presented in the environment.

Microorganism cell structurescan be attacked by ROS, which lead to their damages and finally to cell death.This process is intensified due to the high water content (70–90%).

The article presents the use of photocatalytic ionization to disinfect car air filters. The model studies were performed on the microorganisms (bacteria, yeasts, moulds) from pure culture collections (Aspergillus niger, Escherichia coli, Staphylococcus aureus) and those inhabiting long-used filters (Cladosporium herbarum, Rhodotorula glutinis,  Staphylococcus cohnii). In the research, two levels of relative air humidity were applied. The first (RH=77%) reflected the humidity level with the AC turn on. The second (53%), when the AC is turned off. The conditions of effective photocatalytic ionisation disinfection (R≥99.9%) were established as 2–3h at RH=77% (bacteria) and 6–24h at RH=53% (fungi). The 5% higher microbial number reduction was obtained for higher humidity level. It is caused by the fact that in the photocatalytic ionization process, the main substrate of ROS is water.

The obtained research results show that the photocatalytic ionisation disinfection method may be successfully used to clean filtration materials in cars.

Pietrzak

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