This chapter presents a review on limited studies that have been conducted using advanced oxidation processes (AOPs) in treating biologically treated palm oil mill effluent. Palm oil mill effluent is the byproducts of palm oil production that is normally treated using a series of biological processes. However, despite being treated for a long period of retention time, the effluent still possesses high concentration of organics, nutrients, and highly colored, and will pollute the environment if not treated further. Advanced oxidation processes that utilized hydroxyl radicals as their oxidizing agents have the potential of further treating the biologically treated POME. Fenton oxidation, photocatalysis, and cavitation are the main AOPs that have been studied in polishing the biologically treated POME. Depending on the experimental conditions, the removal of organics, in terms of COD, TOC, and color, could reach up to more than 90%. Nevertheless, each of this process has its own limitations and further studies are needed to overcome these limitations.
