Recent developments in photochemical and chemical AOPs in water treatment: A mini-review

Photochemical and chemical oxidation methods, belonging to a wide group of advanced oxidation processes (AOPs), are extensively studied but still under constant development. The aim of this study was to review the recent developments mainly in UV/H₂O₂ process and Fenton's reactions. Ultraviolet (UV) radiation is an essential factor in photochemical oxidation. In the development of UV radiation sources the energy efficiency and the use of toxicant free materials have become major objectives. Also the emitted wavelength plays a significant role. Besides, there are alternatives for UV radiation sources, such as radio frequency (RF) plasmas, which can operate in water without additional chemicals. A remarkable development in the field of chemical oxidation has been novel catalyst materials for Fenton's reaction enabling the efficient reaction in neutral or almost neutral conditions, instead of pH below 3. In addition, varieties of method integrations, e. g., combinations of AOPs or AOPs integrated to biological processes, and other enhancements such as combining ultrasound (US) with AOP have led to improved water treatment efficiencies.