The research carried out as part of this doctoral dissertation aims to investigate the removal of two micropollutants from water by advanced oxidation processes (AOPs), using high power ultrasound and ozone. The selected micropollutants serve different purposes and belong to distinct groups of compounds – gemfibrozil is a pharmaceutical used as a lipid regulator, while epoxiconazole is a pesticide with both preventative and curative action used for plant protection. According to the Joint Research Centre (JRC), the European Commission’s science and knowledge service, both compounds are considered as contaminants of emerging concern and are identified as potential candidates for the Watch list under the Water Framework Directive for future monitoring due to their occurrence in the environment and lack of data concerning potential harmful effects. Conventional water treatment processes are usually inefficient in removing emerging contaminants. Therefore, AOPs represent a promising alternative in water treatment. They are characterized by the generation of highly reactive hydroxyl radicals (•OH), which are almost non-selective in their reactions with organic compounds and have high reaction rate constants. The use of high power ultrasound as an AOP has been reported to be a highly efficient process for the removal of micropollutants and is considered to be an environmentally-friendly technology since it does not require the addition of chemicals and does not generate waste. Ozonation, on the other hand, is a well-established technology often employed for water disinfection and can be applied as an AOP for the removal of micropollutants under certain conditions where •OH radicals are generated through ozone decomposition. Extensive lab-scale research was conducted with the following objectives: • to determine the efficiency of both AOPs in the removal of selected micropollutants from water by experimentally obtaining the value of reaction rate constant, • to identify the degradation by-products formed, • to propose the reaction pathways of selected micropollutants, • to predict the toxicity of selected micropollutants and their degradation by-products. The dissertation is organized as follows. Chapter 1 provides an introduction outlining the problem statement and the overview of the previous research with the focus on several key areas: detection, identification and occurrence of emerging contaminants in natural and drinking water and wastewater; their fate and transport in natural aquatic environment and the knowledge on their reaction pathways and by-products; identification of potential toxicological effects; mechanisms for the removal of emerging contaminants and treatment technologies that can be effectively used for their removal. Two selected micropollutants, gemfibrozil and epoxiconazole, are presented with details on their specific properties, occurrence in water environment and toxicity data. At the end of the chapter, objectives of the study are stated, the hypothesis is given, and scientific contribution is outlined. Chapter 2 presents the theoretical background for the thesis. It describes advanced oxidation processes with emphasis on the application of high power ultrasound and the phenomenon of acoustic cavitation, responsible for the emergence of sonochemical processes. All parameters that affect the sonochemical degradation of micropollutants are presented in detail. The concepts of chemical dosimetry used for the quantification of OH radicals are described and a model for the determination of OH radicals steady-state concentration is provided. The kinetics of sonochemical degradation is described using mathematical models which consider the complexity of sonochemical process in heterogeneous conditions. The theory on application of ozone as an AOP is presented with the main mechanisms of ozone reactions in water. Its instability in water results in fast decay followed by numerous chain reactions. The most widely accepted decay mechanism of ozone in water is described. Chapter 3 describes the experimental setup for the removal of emerging contaminants using high power ultrasound. It explores the ultrasound performance under different input parameters to optimize experimental conditions for micropollutants degradation (acoustic power determination using calorimetric method, steady-state •OH radicals estimation conducted using terephthalic dosimetry system). It also includes the determination of the optimum concentration of radical scavenger (t-BuOH) which is assumed to scavenge the vast majority of •OH radicals to get the information on the part of the degradation associated with very high temperature pyrolysis. Regarding the application of ozone as an AOP, this chapter describes the experimental setup for preparing the ozone stock solution and the materials and methodologies used for measuring the ozone concentrations, either by direct UV measurement (stock solution) or indigo method. Chapters 4 and 5 present the results of application of high power ultrasound in the degradation of gemfibrozil and epoxiconazole, respectively, in both model and natural water. The results of kinetic experiments were obtained to estimate the observed reaction rate constant. Chapters also include relevant information on the identified degradation by-products and their proposed structures which were used to propose the relevant reaction pathways of gemfibrozil and epoxiconazole degradation upon ultrasonic sonication. The results of toxicity assessments of both micropollutants and their by-products using in silico analyses and mathematical modeling based on the qualitative structure-activity relationship (QSAR) are also presented. Chapters 6 and 7 present the results of using ozone as an AOP in degradation of selected micropollutants. The materials, methods and experimental procedures are based on two degradation mechanisms – the reaction with molecular ozone and the reaction with OH radicals generated through ozone decomposition. The results obtained from separate kinetic experiments provided the degradation rate constants for the reaction of O3 and OH radicals with gemfibrozil and epoxiconazole, respectively. The experiments also showed that gemfibrozil reacts readily with both oxidant species, as opposed to epoxiconazole which showed minimal reactivity towards ozone. Chapter 8 contains a brief discussion on the results of this research and the final conclusions of this thesis.