Solar-Assisted Iron Sludge Photo-Fenton Catalysis for Enhanced Oxidation of Dye-Loaded Beauty Salon Wastewater

Beauty salon wastewater is an emerging commercial greywater characterized by high chemical oxygen demand (COD), intense color, and low biodegradability due to the presence of surfactants and oxidative dye precursors. This study evaluated a solar-assisted photo-Fenton process using waste-derived iron sludge as a heterogeneous catalyst for treating real beauty salon effluent. Operational parameters, including pH, H2O2 concentration, iron sludge dosage, reaction time, and temperature, were optimized based on dye removal and COD reduction. Under optimal conditions (pH = 3, H2O2 = 400 mg L−1, iron sludge = 40 mg L−1), the system achieved approximately 98% dye removal and 95% COD reduction within 50 min of irradiation. Additionally, maximum performance was observed at 40 °C, while higher temperatures reduced efficiency due to non-productive H2O2 decomposition. Kinetic analysis was performed, and the results indicated predominant second-order behavior. Thermodynamic evaluation confirmed an endothermic process with moderate activation energy (Eₐ = 21.8 kJ mol−1). Response surface methodology confirmed strong parameter interactions and high predictive accuracy. The integration of solar irradiation with iron sludge valorization provides a sustainable and decentralized solution for treating dye-loaded beauty salon wastewater.