Effect of solution conductivity on H202 production by pulsed corona discharge in water

Non-equilibrium plasma generated by electrical discharges in liquids initiate various chemical and physical processes that can be potentially utilized in different environmental, biological or medical applications. These processes include high electric field, ultraviolet radiation, overpressure shock waves and, of particular importance, formation of various reactive chemical species such as radicals (OH, H, O) and molecular species (H₂O₂, H₂, O₃), among which OH radicals and hydrogen peroxide are the most important for oxidation processes. The magnitude of the contributions of the individual effects in the decontamination or microbial inactivation processes strongly depends upon the energy of the discharge and also on the solution conductivity. An increase in the solution conductivity is connected with a higher concentration of ions in the liquid, which strongly alter the propagation of the streamer channel in water by compensating the space charge electric field on the streamer head. Thus, higher conductivity results, on the one hand, in a larger discharge current due to lower resistivity of liquid media, and, on the other hand, in a shortening of the streamer channel length due to faster compensation of space charge electric field on the streamer head by ions in the liquid. This results in a higher power density in the discharge channel and a higher plasma temperature and higher UV radiation. Hydrogen peroxide as the most abundant chemical species directly produced by the discharge in water is often utilized in Fenton´s reaction to increase the plasmachemical efficiency of the removal of organic compounds by addition of ferrous salts into treated water. There is also evidence about contribution of H₂O₂ in bacterial inactivation by electrical discharge in water. In the present study, the role of solution conductivity in the hydrogen peroxide production by the pulsed corona discharge in water generat- - ed using point to plane geometry of electrodes is investigated. The free radical scavenging property of DMSO and phenol is used to determine the initial rate of formation of H₂O₂ by the pulsed corona discharge. The influence of UV radiation of the discharge and the effect of H₂ and O₂ on the production of hydrogen peroxide will be discussed.