Contribution of uv photolysis in bactericidal effects of pulsed corona discharge in water

Abstract

UV radiation in the 200-300 nm wavelength range with doses of several mJ/cm2 is known to cause lethal damage of cells. Amongst UV effects on bacteria is the dimerization of thymine bases in their DNA strands. This inhibits the ability of bacteria to replicate properly. The results obtained using the emission spectroscopy showed a radiation from the pulsed corona discharge in water in a wide range of wavelengths (200-1000 nm), which is dominated by the spectral lines of hydrogen and oxygen atom and by emission from OH radical. Electron density above 1018 cm-3 in the streamer discharge has been determined from the Halpha spectral line profile. With increasing water conductivity stronger radiation and higher electron density in the streamer discharge have been determined (above 1019 cm-3). Quantitative analysis of ultraviolet radiation from the pulsed corona discharge in water performed by the potassium ferrioxalate actinometry revealed that significant UV emission from the discharge occurs with increasing solution conductivity and the pulse radiant power of the emitted UV radiation could reach levels of the order of tens to hundreds of Watts per pulse in the range of solution conductivity of 100-500 muS/cm. This radiant power corresponds to UV radiation intensity of the order 0.1-10 mW/cm2. This is a significantly higher intensity level than reported for non- equilibrium air plasma where UV radiation does not play a significant direct role in the sterilization process. This indicates that UV radiation may play an important role in the bacterial inactivation by the corona discharge in water. In this work, the effects of pulsed corona discharge in water on the inactivation of Gram-negative bacteria Escherichia coli and Gram-positive bacteria Enterococus faecalis are investigated. The role and contribution of ultraviolet radiation from the discharge in the overall bacterial inactivation by the electrical discharge in water of two different solution conductivity (200 and 500 muS/cm) are discussed.