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

Abstract A batch photocatalytic study was carried out to inactivate six different species of bacteria using fluorescent light and TiO 2 photocatalyst. Several surface loadings of TiO 2 varying from 234 to 8662 mg/m 2 , 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 TiO 2 loading, the maximum inactivation of most bacteria was achieved at an optimum TiO 2 loading of 511–1666 mg/m 2 , corresponding to a thickness of 294–438 nm of TiO 2 layer on the surface. 100% of the E. coli K-12 was inactivated after 30 min of treatment at a TiO 2 loading of 1666 mg/m 2 , while inactivation of 1 log 10 was obtained for Microbacterium sp., Paenibacillus sp. SAFN-007 and Microbacteriaceae str. W7 after 2 h of illumination at a TiO 2 loading of 1116 mg/m 2 .