Degradation Of Dyes In Aqueous Solution Using High-Voltage Pulsed Discharges

Over the recent years there has been a growing interest in the development of pulsed high-voltage discharge method for degrading toxic organic contaminants in water. The objective of the present work is to perform a fundamental investigation on degrading organic dyes in water using this method. It was composed of two parts: part one, three kinds of discharge types were produced and effects of them on degradation efficiency were investigated; part two, a novel technique combined with liquid and gas phase discharges for dyes degradation in aqueous solution was developed.Part one, corona, mixed and spark discharges in water were defined by the pulsed high-voltage discharge phenomenon. The discharge types induced by the various operation conditions have been examined. Spark discharge was easily occurred with applied voltage increasing, gas flux increasing, electrode distance decreasing and liquid conductivity decreasing. The conditions such as applied voltage and liquid conductivity have important roles on degradation efficiency of cationic red X-GRL. Higher degradation efficiency of organic dyes has been achieved by spark discharge. The degradation efficiency was greatly enhanced with a dosage of H2O2 addition and was not enhanced with TiO2. The apparent production of OH radicals and quantum yields generated by spark discharge in distilled water were 11.57 umol/L and 0.0978 photon/s, respectively. The processes of degradation showed that the oxidative effects through OH radical oxidation did not play an important role and did weaken with the discharge type changing to corona discharge.Part two, the technique of combined with liquid and gas phase discharges (LGD) using pulsed high voltage was developed. In this system, the apparent synergistic effects for acid orange II (AO) degradation in the presence of oxygen were observed. The enhancement of degradation rate for AO was around 302%. Furthermore, higher energy efficiency can be obtained in comparison with individual liquid phase discharge (LD) or gas phase discharge process (GD). Important operating conditions such as electrode distance, applied voltage, pulse repetition rate, and types of dyeswere also investigated. The AO degradation in the presence of oxygen by LGD may proceed through the direct ozone oxidation and the decomposition of the ozone induced by the liquid phase discharges.