Degradation of Congo red dye by ozonation

The purpose of this study was to investigate the degradation of azo dye in synthetic wastewater by ozonation and to optimize the reaction parameters such as pH, time and type of catalysts which influence the efficiencies of color and COD removal. Congo red dye was selected as model pollutant. Catalytic and non-catalytic ozonation of Congo red dye were carried out in batch reactor with constant ozone flow rate of 36 mg/h. Cu(NO3)(2), Ni(NO3)(2), Fe(NO3)(3), Cu/Al2O3 and Cu/SiO2 were used as catalysts for the catalytic ozonation system. It was observed that over 85% of Congo red could be removed within 1 h for all ozonation conditions. Higher color removal could be achieved when ozonation was carried out in alkaline (pH 10) and acidic (pH 4) condition as compared to in neutral (pH 7) condition. The reduction of COD was more than 60% for both catalytic and non-catalytic ozonation in 2 h. The catalytic ozonation using Cu(NO3)(2) as catalyst showed the highest efficiency as it gave the 90% of color removal in 48 min with 60% of COD reduction. However, with catalyst, efficiencies of color decomposition are higher in alkaline and neutral conditions than in acidic condition. The ozonation of dye was found dominant by pseudo-first-order reaction at room temperature.