DEGRADATION OF TEXTILE AZO DYE ACID ORANGE 7 BY ADVANCED OXIDATION PROCESS

Abstract

The present study was undertaken to determine the feasibility of Advanced Oxidation Processes (AOPs) in treatment of textile dyes in wastewater. Acid Orange 7 (AO7) is an azo dye with potential ecotoxicity to the exposed organisms. Natural attenuation, photo –catalytic degradation (with TiO2), and Fenton’s treatment were studied as AOPs for effective degradation of AO7. The Experimental results confirmed that natural attenuation under sunlight and shade is not an effective process for degradation of AO7. It was observed that a fraction of dye is degraded/ transformed during the day time with exposure to sunlight but the colour regenerated during night time. Photo – catalytic degradation with TiO2 was found to be higher than without TiO2 but the rate of degradation was quite low. The dose of photo – catalyst regulates dye degradation and the concentration 1.0 g/l of TiO2 was observed to have maximum degradation of 76% in a period of about 32 hours. Complete decolourisation was observed in a period of about 127 hours. The recovery of photo – catalyst was found to be 62% for its reuse. The decolourisation of Acid Orange 7 dye by Fenton’s oxidation process was observed to be dependent on several process variables. Concentration of Hydrogen peroxide, Ferrous sulphate, pH, and contact time were considered in this study. Preliminary experimental runs were carried out using univariate approach. It was found that minimum contact time for complete decolourisation by varying H2O2 concentration was obtained at 5 mmol/l. Increase in FeSO4 (mg/l) concentration resulted in decrease of time for complete decolourisation; but an increase above 38 mg/l resulted in precipitation of Fe3+, thereby reducing decolourisation. Maximum decolourisation was observed at pH 3.0. The experimental Box – Behnken Design was used to validate and optimize the process variables. Maximum and minimum levels of pH (3 – 5), H2O2 (4 – 6 mmol/l), FeSO4 (30 – 46 mg/l) and contact time (5 – 15 minutes) were used. The statistical analysis revealed a value of 0.88 for coefficient of regression (R2) indicating a good fit of model. Calculated F – value was found to be higher than the tabulated value confirming to significance of the model. Based on student’s t – test, Ferrous sulphate, pH, and contact time have a positive effect on the percent decolourisation of Acid Orange 7. The optimised values were H2O2 concentration = 4.97 mmol/l, FeSO4 = 40.83 mg/l, pH = 3.1 and contact time = 13.6 minutes. Comparison of different AOPs revealed that Fenton’s process is the most efficient treatment method for degradation of AO7.