Hydroxyl radicals are produced with the help of one or more primary oxidants (e.g. ozone, hydrogen peroxide, oxygen) and/or energy sources (e.g. ultraviolet light) or catalysts (e.g. titanium dioxide).
In general, when applied in properly tuned conditions, AOPs can reduce the concentration of contaminants from several-hundreds ppm to less than 5 ppb and therefore significantly bring COD and TOC down, which earned it the credit of "water treatment processes of the 21st century".
[4] The AOP procedure is particularly useful for cleaning biologically toxic or non-degradable materials such as aromatics, pesticides, petroleum constituents, and volatile organic compounds in wastewater.
Nevertheless, its high oxidative capability and efficiency make AOPs a popular technique in tertiary treatment in which the most recalcitrant organic and inorganic contaminants are to be eliminated.
[citation needed] The reaction, using H2O2 for the formation of ·OH, is carried out in an acidic medium (2.5-4.5 pH)[9] and a low temperature (30 °C - 50 °C),[10] in a safe and efficient way, using optimized catalyst and hydrogen peroxide formulations.
As long as there are sufficient ·OH radicals, subsequent attacks on compound F will continue until the fragments are all converted into small and stable molecules like H2O and CO2 in the end, but such processes may still be subject to a myriad of possible and partially unknown mechanisms.
For instance, doping TiO2 with non-metallic elements could possibly enhance the photocatalytic activity;[20] and implementation of ultrasonic treatment could promote the production of hydroxyl radicals.