Allura Red dye degradation using hybrid advanced oxidation methods

The Allura Red dye is classified as an azo-type dye, known for its carcinogenic and mutagenic properties. It is commonly discharged into the environment through various industrial effluents, including those from the textile, food, drug, and cosmetic industries. This study is focused on investigating the degradation of Allura Red dye utilizing advanced oxidation techniques such as hydrogen peroxide, Fenton, hydrodynamic cavitation (HC), and hybrid methods (HC/H₂O₂ and HC/Fenton) for the first time. Initially, the study examined individual process parameters including pH, H₂O₂ concentration, Fe²⁺/H₂O₂ ratio, and inlet pressure to determine their optimal values for maximum dye degradation. The highest degradation of the dye, reaching 68.9%, was achieved with an H₂O₂ concentration of 11.47 × 10^–3 mol. L⁻¹ at pH = 3. Fenton reagent (Fe² + /H₂O₂) achieved a degradation rate of 85.90% at a molar ratio of 1:30. Inlet pressure was found to significantly affect the HC-based method, with maximum degradation observed at 5 bar and pH = 3, resulting in a degradation efficiency of 76.48% over 90 min. Subsequent experiments with HC/ H₂O₂ and HC/Fenton conducted at 5 bar pressure and pH 3 revealed maximum degradation rates of 97.6% in 120 min and complete decolorization within 1 min for HC/Fenton. HC/Fenton also demonstrated the highest reduction in chemical oxygen demand (COD) at 76.43%. Kinetic analysis indicated that the degradation followed pseudo-first-order kinetics for all methods, with the HC/Fenton process exhibiting the fastest rate constant of 2.99 × 10^–2 min⁻¹. Additionally, the electrical energy efficiency of HC-based methods was evaluated and compared. The study suggests that the HC/Fenton process shows promise for efficiently treating dye-contaminated water.