Destruction of endocrine disrupting compounds in water by advanced oxidation processes: a study with ultrasound, ozone and various combinations

Abstract

The presence of endocrine disrupting compounds (EDCs) in the environment is a significant health concern due to their potential to mimic the hormonal activity in wildlife. Their elimination in water by conventional water treatment methods is very difficult, so that extensive research has been recently devoted to the development of appropriate and effective methods for the complete destruction of the compounds or for removing their endocrine activities. Due to the high reactivity of hydroxyl radicals with all organic chemicals regardless of their complexity, advanced oxidation processes that are based on the onsite generation of these radicals have gained much attention in recent years for the destruction of problematic pollutants in water such as EDCs . The aim of this study was to investigate the degradability of EDCs primarily by ultrasound, which is a novel technique of hydroxyl radical production. In addition, ozonation and hybrid techniques involving combinations of ultrasound with ozone and/or with Fenton reactions were also evaluated as alternative methods. The test compounds were selected from a group of well classified EDCs (Bisphenol-A and 4-n-Nonylphenol) and a group of nonclassified but suspected EDCs (a textile dye-C.I. Acid Orange 8). The emphasis was on: i) effects of operating parameters such as EDC concentration, pH, ultrasonic frequency, the dose of chemical reagents; and ii) reaction kinetics and reaction sites. It was found that the rate of EDC decay was pseudo-first order in all experimental systems and at all test conditions. Ozonation at pH 6 was a very effective method of converting EDCs to products, which did not exhibit endocrine disrupting properties. The efficiency of ultrasonic destruction of EDCs was largely related to the physical properties of the compounds (e.g. hydrophobicity), the applied frequency, the type of dissolved gases in the medium and the pH of the solution. Addition of OH radical sinks (e.g. carbonates, tertiary butyl alcohol) and OH radical sources (e.g. Fenton reagents, carbon tetrachloride) at the right doses was a key parameter in controlling the reactivity of EDCs under ultrasonic irradiation. Combination of ultrasound with ozone induced a synergistic effect particularly for the overall degradation or mineralization of the compounds.