Advanced oxidation processes (AOPs) are a set of chemical treatment methods designed to remove organic pollutants from water and wastewater. These processes typically involve the generation of highly reactive species, such as hydroxyl radicals, which can effectively break down complex contaminants into simpler, less harmful substances. AOPs are often used in conjunction with other treatment methods to enhance overall efficiency. Common techniques used in AOPs include ozonation, Fenton's reagent, and photocatalysis. Each method varies in its approach to generating reactive species, but all aim to achieve high levels of oxidation. AOPs are particularly effective for treating recalcitrant compounds that are resistant to conventional treatment methods.