Effectiveness of Photocatalytic Decolourization of Reactive Red 120 Dye in Textile Effluent Using UV/H₂O₂

The effectiveness of Advanced Oxidation Process (AOP) for degradation of reactive red 120 dye in aqueous solutions was tested in this present study. Ten different concentrations of the reactive red 120 dye were exposed to UV alone and a combination of UV with two different concentrations (10 ml/L and 20 ml/L) of H₂O₂ for 10 different retention times at the pH of textile effluent (pH = 10-11). The effect of acidifying the dye solution on the removal efficiency was also investigated. The COD removal efficiency was determined for the most efficient treatment. The dye degradation efficiency obtained after 60 min exposure to UV alone was 27.01% for 50 mg/L dye concentration and 0.33% for 500 mg/L dye concentration. The degradation efficiency obtained after exposure to UV/10 ml/L H₂O₂ 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 a degradation efficiency of 99.96% after 20 min for the 50 mg/L dye concentration and 99.95% after 60 min for the 500 mg/L dye concentration. Increasing the H₂O₂ from 10 ml/L to 20 ml/L (UV/20 ml/L H₂O₂) improved the oxidation efficiency and reduced the treatment time. The Chemical Oxygen Demand (COD) analysis performed on the effluent obtained from the UV/20 ml/L H₂O₂ treatment showed a COD removal efficiency of 99.96% (from 704 mg/L to 416 mg/L) after 20 min for the 50 mg/L dye concentration and 99.95% (from 1184 mg/L to 256 mg/L) after 60 min for the 500 mg/L dye concentrations. However the final COD concentrations were higher than the COD discharge limit of 80 mg/L. The COD discharge limit of 80 mg/L could be achieved with UV/ 20 ml/L H₂O₂ treatment by increasing the exposure time (longer than 60 min). The pH of the treated effluent is within the accepted discharge limit of 6-9. Treatment of the dye effluent under acidic condition was slightly faster but the time reduction does not justify the cost of chemicals addition to adjust the pH to 3 before treatment and then to 7 and the further treatment to remove these chemicals before disposal.