Disinfection of Water and Solid Surfaces: Possibilities for Deep Degradation of Phenol and Tetracycline by Corona Electric Discharge

Abstract

Purification of drinking water from low concentrations of pharmaceuticals and disinfection of hard-to-reach objects is becoming in demand at present. The most promising way is to use hydroxyl radicals (advanced oxidation technologies) for these purposes. In a corona electric discharge in air, in the presence of water vapor, an ozone-hydroxyl mixture is formed, in which the lifetime of hydroxyl radicals is up to 1 s. This makes it possible to transport hydroxyl radicals outside the reactor to come into contact with the liquid or surface to be treated. Ozone is used to keep hydroxyl radicals alive. The oxidizing and antimicrobial ability of the ozone-hydroxyl mixture generated by corona electric discharge was studied using for example degradation of tetracycline, phenol, and disinfection of solutions and surfaces. Generators with seven discharge electrodes (liquid volume 50 mL) and 49 electrodes (liquid volume 80 L) were used. Deep oxidation of tetracycline to the level of 10-3 mg/L was obtained at a dose of 140 J/(50 mL). The dose at which the concentration of tetracycline is halved is $D_{1/2} = 12~\pm ~2$ J/(50 mL). The energy yield for 50% conversion at an initial concentration of 10 mg/L is $G_{50} = 10~\pm ~3$ mg/kWh. In the case of phenol, purification was obtained to a level of 0.018 mg/L at a dose of $5\times 10^{4}$ J/(50 mL). Inhibition of the oxidative reaction associated with the course of reverse reactions was observed. The decontamination of solutions and surfaces infected with gram-positive and gram-negative bacteria was studied. The energy cost to reduce the colony-forming unit (CFU) by ten times is 59±11 J/(100 mL), and under the conditions of this experiment, it does not depend on the initial concentration of bacteria. Water treated with an ozone-hydroxyl mixture has antimicrobial properties that allow surfaces to be disinfected by irrigation. In the case of liquid treatment, it is preferable to use a storage tank and circulate the aqueous solution through an ozone-hydroxyl mixture generator.