INTEGRATED ADVANCED OXIDATION PROCESSES FOR PERSISTENT AZO DYE METHYL RED DEGRADATION: SYNERGISTIC EFFECTS OF UV PHOTOLYSIS, H2O2, AND IRON-BASED SYSTEMS

Abstract

The contamination of industrial wastewater with persistent azo dyes like methyl red (MR) poses a significant environmental challenge, as conventional treatments often fail to achieve complete degradation. Advanced oxidation processes (AOPs) offer an effective alternative by generating hydroxyl radicals (•OH) to break down pollutants. This study investigates the efficiency of various AOPs for MR degradation, comparing UV photolysis, hydrogen peroxide (H₂O₂) oxidation, UV/H₂O₂, and iron-based catalytic processes, including Fenton (Fe²⁺/H₂O₂), Fenton-like (Fe³⁺/H₂O₂), Photo-Fenton (UV/Fe²⁺/H₂O₂), and Photo-Fenton-like (UV/Fe³⁺/H₂O₂).

UV photolysis, at 254 nm, resulted in limited MR degradation (23.7% at 0.01 g/L), while H₂O₂ oxidation reached 35% efficiency at 0.01 M, though excessive peroxide led to radical scavenging. The UV/H₂O₂ system significantly enhanced MR degradation (84.3% at 0.01 M H₂O₂) due to increased hydroxyl radical production. The Fenton process (Fe²⁺/H₂O₂) achieved near-complete degradation (99.5%) at a 1:5 Fe²⁺/H₂O₂ ratio under acidic conditions (pH 3). In contrast, the Fenton-like process (Fe³⁺/H₂O₂) was slightly less effective (85%) due to the slower reduction of Fe³⁺. Photo-Fenton treatment (UV/Fe²⁺/H₂O₂) further accelerated MR removal, achieving nearly complete degradation within 30–40 minutes. Similarly, the Photo-Fenton-like process (UV/Fe³⁺/H₂O₂) improved upon its conventional counterpart, reaching 95% degradation at a 1:5 ratio within 60 minutes.