Mechanisms and modelling of sonochemically-mediated free radical degradation of contaminants

Abstract

Hazardous and recalcitrant pollutants in the environments have led to a great many environmental issues these days. Many researchers have focused on the approaches to treatment of these pollutants which contaminate environments such as soil, surface and groundwater. As an advanced oxidation processes (AOPs), sonolysis which is the oxidation technology involving the use of ultrasonic irradiation, has proven to be successful for the treatment and remediation of contaminated environments.

In this thesis, hydrogen peroxide formation and formic acid degradation by ultrasonic irradiation of well-characterised solutions are described under various conditions in order to determinate reaction mechanism by which peroxide degradation and contaminant degradation occur. The effect of gas properties and frequency on hydrogen peroxide and formic acid degradation are examined. Experimental results obtained are analyzed in light of the reactions occurring. Successful mathematical modeling of the result s obtained confirms that, for the most part, hydrogen peroxide and formic degradation occur by free radical generation within bubbles with subsequent transfer of these radicals to the bubble-water interface where the majority of the degradation occurs. The effect of Fe(II) addition which can lead to Fenton reactions in the bulk solution are also investigated. Experimental and model results show that the heterogeneous reactions can enhance the degradation of formic acid in the presence of Fe(II).

Oxidation of phenol by ultrasonic irradiation under a variety of initial conditions and solution environments is also described and validated by a simple kinetic model. The model developed will be useful for improving our understanding of free radicals behaviour and the interplay between free radical generation and contaminant degradation.