Effect of intermittent 222 nm krypton-chlorine excilamp irradiation on microbial inactivation in water

In order to assure the microbial safety of drinking water, krypton-chlorine (KrCl) excilamp treatment has emerged as a possible technology to replace the use of conventional 254-nm low-pressure mercury UVC lamps. The aim of this study was to evaluate the disinfection efficiency of the KrCl excilamp emitting power narrow-band UVC radiation at 222-nm against a spectrum of bacteria at different initial populations in model contaminated water and to develop a strategy to effectively sterilize water contaminated with high concentrations of microorganisms. Different inoculum levels (104−5, 105−6, and 106−7 CFU/ml) of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes suspended in sterile distilled water were irradiated with a KrCl excilamp. In water of high inoculum density (106−7 CFU/ml), higher resistance to UVC was observed than in samples of medium and low cell density, as a high concentration of suspended cells lowered the transmittance of UVC rays. However, intermittent application of 222-nm UV irradiation in water containing a high inoculum level showed higher inactivation capacity against all three pathogens than continuous irradiation at the same dose. The results of this study provide an interesting insight into the use of an intermittent 222-nm UVC treatment system in batch-type water reservoir facilities to reduce the risk of waterborne disease.