Decolorization Of Simulated Dye Solution By Ozonation In Combination With Ultrasonic Radiation

Azo dyes are widely used in a variety of industries from textile to paper. The major sources of dyes in the environment are effluents from the textile industry and some dyes may have carcinogenic and/or teratogenic effects on public health. The disposal of dye wastewater is an environmental concern. Most of the dyes are found to be resistant to normal treatment process as they are designed to resistant to chemical and photochemical degradation. Ultrasonic radiation has been demonstrated to increase the mass transfer of ozone to solution by means of increasing volumetric mass transfer coefficient. So coupling of ultrasonic radiation with ozonation (US/O3) may provide a possible advanced oxidation process (AOP).In this study, methyl orange was chosen as the model contaminant and efficiency in different reaction systems was investigated. The effect of following operating conditions on decolorization efficiency were also investigated: ultrasonic powers, initial dye concentrations, ozone gas concentrations, initial pH values, radical scavenger(Na₂CO₃ ) . The decolorization kinetic mode was established to determine second order rate constant and mass transfer coefficient of ozone in US/O3 system. The absorption and decomposition of O3 with and without ultrasound were conducted to investigate the effect of ultrasonic waves on the mass transfer of ozone. Mathematical model was proposed to determine rate constants of ozone self-decomposition in water and mass transfer coefficient of ozone. Further, the influence of pH, US Power, the inlet ozone concentration, the inlet gas flowrate on mass transfer were also observed. Based on the experiment, we can get the following conclusions:(1) Ozonation in combination with ultrasound radiation has synergistic effect on the decolorization of methyl orange. The decolorization of methyl orange fits the apparent pseudo first order kinetic model. The effect of pH on the decolorization was insignificant when pH ranged from 5.5 to 9.7. The presence of hydroxyl radical scavenger had little influence on the decolorization rate, which indicates that the primary mechanism is not the reaction involved in radicals formed in the sonozone process but direct decomposition by ozone. The decolorization efficiency increased with increasing ultrasonic power, gasflow rate, and gaseous ozone concentration. However, the decolorization efficiency decreased with increasing initial dye concentration.(2) To determine rate constants and the mass transfer coefficients of ozone, mathematical model was established. It was found that US enhanced mass transfer of ozone .Mass transfer coefficient increased with increasing US power as well as gas flowrate.(3) The absorption and decomposition of O3 with and without ultrasound were conducted to observe the effect of ultrasonic waves on the mass transfer of ozone and degassing of O3 by ultrasound was also investigated. The results showed that both mass transfer coefficient and self-decomposition rate constant of ozone was enhanced by ultrasound. The rate constant of ozone self-decomposition increased with the increment of pH. However, the effect of pH on the mass transfer coefficient was insignificant. Increasing the gas flow rate corresponded to increment of K_La₂ There was no remarkable influence on both mass transfer coefficient and self-decomposition rate constant of ozone when we changed the gaseous ozone concentration. In addition, the degassing due to ultrasound occurred in the decomposition process of O₃, but it was minimized considerably during the course of ozone absorption.