The researchers used advanced Fenton oxidation to clean up heavy oil wastewater that was hard to treat with regular methods. By adjusting the amounts of H2O2 and Fe2+, oxidation time, pH, and dosing method, they found that they could remove over 74% of the pollutants, bringing the effluent COD down to 58.9 mg/L. This meets the discharge standard completely. Adding the chemicals all at once worked best, and doing so multiple times improved the cleanup even more.