Generation of discharges in dynamic foam for oxidants formation using various types of electrodes

An innovatory apparatus for the discharge generation in foaming conditions was constructed. The main goal of the research was to obtain various kinds of oxidants, useful in Advanced Oxidation Processes (AOP) in one compact reactor, potentially even in the treated medium. Such an application of dynamic foam, created without the addition of surfactant has not been investigated as yet. To find the optimum conditions for the efficient foam generation and the discharge development and moreover, to assure the presence of oxidants in sufficient concentrations several electrode materials and electrode set-ups were tested. The experiments were done in the metal plate-to-metal plate, metal plate-to-dielectric plate, needles-to-metal plate and needles-to-dielectric plate electrodes’ set-ups. The discharge gap space ranged from 4 mm in the case of plate-to-plate electrodes to 7 mm in the case of needles-to-plate electrodes. Generally, the highest oxidants’ concentrations at the highest comparable gas flow rate were obtained in the needles-to-dielectric plate arrangement, where 521 and 875 ppm of gaseous ozone, 0.36 and 0.5 mg dm−3 of dissolved ozone and 59 and 62 mg dm−3 of hydrogen peroxide were obtained at 14 kV of applied voltage and at 5 dm3 min−1 of the substrate gas flow in air and oxygen, respectively. The presence of OH radicals was confirmed by the spectroscopic measurements. The larger gap size was more advantageous from the foam formation point of view and the dielectric layer assured more uniform spatial discharge development between the electrodes.