저온 플라즈마를 이용한 폐수중의 유기물 분해에 관한 연구

Abstract

This study investigated the degradation of organic contaminants in a synthetic wastewater by using dielectric barrier discharge (DBD) plasma. When electrical discharge occurs, the DBD reactor produces oxidative species like ozone and emits ultraviolet (UV) light. The DBD reactor of this study consisted of a quartz dielectric tube and a coaxial copper rod (or water-filled glass tube), which was submerged in the wastewater. High voltage was connected to the copper rod (discharging electrode) while the wastewater was grounded. In this configuration, the wastewater acting as the ground electrode was in a direct contact with the outer surface of the quartz tube. The UV light produced in the DBD reactor was able to irradiate the wastewater since the quartz tube was transparent to it. Before carrying out the degradation of the organic contaminants, the characteristics of the DBD reactor in terms of the UV emission and ozone production were investigated with such variables as electrode material (water or metal) and discharge power. For the purpose of efficiently using the UV light for the degradation, a photocatalyst (aluminum meshes coated with titanium oxide) was employed. The chemically active species (mostly ozone) produced in the DBD reactor were well distributed in the wastewater using a porous gas diffuser to increase the gas-liquid contact area. It was found that the water-filled glass tube (aqueous electrode) was more energy-efficient for the production of ozone, probably because the contact between the aqueous electrode and the dielectric surface was so perfect that the loss of the electrical energy could be minimized. Another reason that may explain this result is the difference in the mode of discharge. The electrical discharge with the aqueous electrode occurred in a glow mode while that with copper electrode formed a number of plasma filaments. It is believed that evenly distributing the energy over the discharge volume is more desirable than concentrating it into the plasma filaments. The synthetic wastewater for evaluating the performance of the present DBD system was formed with distilled water and azo dyes such as Amaranth and Acid Red 4. The experimental parameters chosen were the concentration of the electrolyte in the aqueous electrode, the voltage applied to the DBD reactor, the initial pH of the wastewater, and the concentration of hydrogen peroxide added to the wastewater. The results have clearly shown that the present system capable of degrading organic contaminants in two ways (DBD-induced photocatalysis and ozonation) may be a promising wastewater treatment technology.