Efficiency of KrCl excilamp (222 nm) for inactivation of bacteria in suspension

To examine the killing efficiency of UV KrCl excilamp against Gram-positive and Gram-negative bacteria. Vegetative cells of Bacillus cereus, Bacillus subtilis, Escherichia coli O157:H7, Staphylococcus aureus and Streptococcus pyogenes at initial populations from 10² to 10⁷ colony-forming units (CFU) ml⁻¹ were treated by KrCl excilamp in sterile Ringer's solution with and without H₂O₂. The number of viable cells was determined using spread plating techniques and nutrient agar method with subsequent incubation at 28°C or 37°C for 24 h. At estimated populations of 10²-10⁵ CFU ml⁻¹E. coli O157:H7 and Staph. aureus were the most sensitive and showed 100% disinfection within 15 s (29·2 mJ cm⁻²). Bacillus subtilis was more sensitive to UV treatment than B. cereus. The UV/H₂O₂ inactivation rate coefficients within this population range were two times higher than those observed for UV treatment alone. No effect of H₂O₂ was observed at 10⁷ CFU ml⁻¹ for Bacillus sp. and Strep. pyogenes. The narrow-band UV radiation at 222 nm was effective in the rapid disinfection of bacteria in aqueous suspensions. KrCl excilamps represent UV sources which can be applied for disinfection of drinking water in advanced oxidation processes.