Bacterial Inactivation by Pulsed Corona Discharge in Water

Abstract

Summary form only given. Recently, the pulsed high voltage discharges generated directly in water have been demonstrated to initiate a variety of chemical and physical effects. These include ultraviolet radiation, overpressure shock waves, high electric field and, in particular, formation of chemically active species such as OH, H and O radicals and hydrogen peroxide H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> molecules. These physical and chemical processes in turn have been shown to be effective at degrading a variety of organic compounds and also in the inactivation and destruction of microorganisms in water. The mechanism of degradation of organic compounds was found to be attributed mainly to the oxidation by hydroxyl radicals produced directly by the discharge or indirectly from plasma chemically produced hvdrogen peroxide (i.e. due to decomposition of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in the presence of iron ions). There is also evidence about contribution of reductive species HO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and H radicals in the removal of chemical compounds by the discharge in water. On the other hand, less is known about mechanisms of sterilization by means of electrical discharge in water. In general, it is expected that, in addition to the chemical effects, the physical processes such as high electric field and ultraviolet radiation from the discharge significantly contribute in the inactivation of microorganisms. There are also possible synergistic effects of combined action of chemical and physical processes on the destructive efficiency of the 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 were investigated. A comparison of inactivation efficiency determined in three different types of electrical discharge reactor configurations will be made. The role and contribution of physical processes (such as ultraviolet radiation from the discharge and pulsed electrical field in the discharge chamber) and of plasmachemically produced hydrogen peroxide in the overall bacterial inactivation by the electrical discharge in water will be discussed.