Chemical oxidation technologies are defined as the processes that use oxidizing agents to degrade or transform complex hazardous chemicals to simpler nontoxic ones. Advanced oxidation processes (AOPs) constitute, in general, the generation and the use of hydroxyl radicals (^•OH) to oxidize hazardous chemicals, which are otherwise very recalcitrant to conventional oxidation processes.

Advanced oxidation processes have been used for the treatment of drinking water, wastewater, and soil/groundwater contaminated with unwanted and hazardous substances. The processes are, in general, based on the generation and the use of highly reactive hydroxyl radicals (^•OH) that react indiscriminately with many organic and inorganic substances. This entry provides the readers with an overview of such AOPs in terms of fundamentals of the reaction mechanisms and their application to drinking water, wastewater, and soil/groundwater treatment processes.