Wet oxidation of high-concentration reactive dyes

Advanced oxidation methods were used to degrade reactive dyes at high concentrations in aqueous solutions. Wet peroxide oxidation (WPO) was found to be the best method in terms of the removal of color and total organic carbon (TOC). Reactive blue (Basilen Brilliant Blue P-3R) was chosen as a model dye for determining the suitable reaction conditions. The variables studied include reaction temperature, H₂O₂ dosage, solution pH, dye concentration, and catalyst usage. The removal of TOC and color by wet oxidation is very sensitive to the reaction temperature. At 150 °C, the removal of 77% TOC and 90% color was obtained in less than 30 min. The initial TOC removal rate is proportional to the H₂O₂ dosage. The TOC removal is insignificant even when 50% of the stoichiometric amount of H₂O₂ is used. No color change is observed until the dosage of H₂O₂ is 100% of the stoichiometric amount. The color removal is closely related to TOC removal. When the pH of the solution is adjusted to 3.5, the dye degradation rate increases significantly. The rates of TOC and color removal are enhanced by using a Cu²⁺ catalyst. Another four reactive dyes, Procion Red PX-4B, Cibacron Yellow P-6GS, Cibacron Brown P-6R, and Procion Black PX-2R, were treated at 150 °C using WPO. More than 80% TOC was removed from the solution in less than 15 min. The process can remove the colors of all these dyes except Procion Black PX-2R.