Treatment of Textile Effluent Containing Reactive Red 120 dye using Advanced Oxidation

Abstract

Disposal of textile effluents into nature is one of the major environmental concerns of a textile industry. Several biological, physical and chemical methods for degradation of textile effluents are being followed, but the real challenge is to find a method that is effective, comparatively fast and cost effective. Advance oxidation is an emerging field that uses oxidants producing hydroxyl radicals to oxidize toxic compounds into non-harmful by-products. The effectiveness of photoxidation on reactive red 120, a widely used complex structured cotton dye, was evaluated. Dye concentrations in the range of 50-500 mg/L were treated with UV alone, TiO2/UV and H2O2/UV under 12 different residence times (5.2-60 min). The best combination was selected for Chemical Oxygen Demand (COD) analysis to determine the amount of chemicals retained in the effluent after treatment. The textile industry produce effluents with a pH of 10-11 and hence, the dye pH was adjusted to 10-11. The maximum degradation obtained with UV alone was 27.01% after 60 min for the 50 mg/L dye concentration and 0.33% after 60 min for the 500 mg/L dye concentration. The maximum degradation obtained with UV/TiO2 was 46.07% after 60 min for the 50 mg/L dye concentration and 2.84% after 60 min for the 500 mg/L dye concentration. The maximum degradation obtained with UV/ 10 ml/L was 99.83% after 25.4 min for the 50 mg/L dye concentration and 99.70% after 60 min for the 500 mg/L dye concentration. Exposure to UV/ 20 ml/L H2O2 resulted in 99.96% degradation after 20 min for the 50 mg/L dye concentration and 99.95% degradation after 60 min for the 500 mg/L dye concentration. Increasing the concentration of H2O2 from 10 to 20 ml/L improved the oxidation efficiency and reduced the reaction time. The COD analysis performed on the samples obtained after UV/ 20 ml/L H2O2 treatment showed a decrease in the COD (from 996 mg/L to 416 mg/L in 20 min for 50 mg/L dye concentration and from 1399 mg/L to 256 mg/L in 60 min for 500 mg/L dye concentration) indicates a much lower COD level could be attained when the effluent is exposed to UV/20 ml/L H2O2 for more than 60 min. Treatment of the dye effluent under acidic condition reduces the reaction time but does not justify the cost of the chemical addition to control the pH and the further treatment to remove these chemicals.