Photocatalytic inactivation of Gram-positive and Gram-negative bacteria using fluorescent light

A batch photocatalytic study was carried out to inactivate six different species of bacteria using fluorescent light and TiO2 photocatalyst. Several surface loadings of TiO2 varying from 234 to 8662 mg/m2, impregnated on membrane filters were used with fluorescent light of constant illuminance of 3900 lux for the inactivation of four ATCC bacteria (Escherichia coli K-12, Pseudomonas fluorescens, Bacillus subtilis and Microbacterium sp.) and two other species of bacteria collected from outdoor air in Singapore (Microbacteriaceae str. W7 and Paenibacillus sp. SAFN-007). Gram-negative bacterium E. coli K-12 was the most effectively inactivated, while Gram-positive B. subtilis exhibited the least response to the photocatalytic treatment. The inactivation rate increased with an increase in the TiO2 loading, the maximum inactivation of most bacteria was achieved at an optimum TiO2 loading of 511–1666 mg/m2, corresponding to a thickness of 294–438 nm of TiO2 layer on the surface. 100% of the E. coli K-12 was inactivated after 30 min of treatment at a TiO2 loading of 1666 mg/m2, while inactivation of 1 log10 was obtained for Microbacterium sp., Paenibacillus sp. SAFN-007 and Microbacteriaceae str. W7 after 2 h of illumination at a TiO2 loading of 1116 mg/m2.