Treatment of wastewater from a cotton dyeing process with UV/H₂O₂ using a photoreactor covered with reflective material

Wastewater containing several dyes, including sulfur black from the dyeing process in a textile mill, was treated using a UV/H₂O₂ process. The wastewater was characterized by a low BOD/COD ratio, intense color and high acute toxicity to the algae species Pseudokirchneriella subcaptata. The influence of the pH and H₂O₂ concentration on the treatment process was evaluated by a full factorial design 2² with three replicates of the central experiment. The removal of aromatic compounds and color was improved by an increase in the H₂O₂ concentration and a decrease in pH. The best results were obtained at pH 5.0 and 6 g L⁻¹. With these conditions and 120 min of UV irradiation, the removal of the color, aromatic compounds and COD were 74.1, 55.1 and 44.8%, respectively. Under the same conditions, but using a photoreactor covered with aluminum foil, the removal of the color, aromatic compounds and COD were 92.0, 77.6 and 59.4%, respectively. Moreover, the use of aluminum foil reduced the cost of the treatment by 40.8%. These results suggest the potential application of reflective materials as a photoreactor accessory to reduce electric energy consumption during the UV/H₂O₂ process.