عنوان مقاله [English]
Most dye substances are used in production processes and cause serious environmental pollution when discharged into the environment. Acid orange 7 is one of them, which has been studied in this research. Acid orange 7 containing wastewater is resistant to aerobic degradation and, under anaerobic conditions, can be reduced to potentially carcinogenic aromatic amines. Physical processes have difficulty in complete destruction of dye pollutants. Applications of both the slurry process and immobilized nano technology systems have recently been studied. Nano material agglomeration, light penetration in wastewater and the separation of nano materials from effluent are the most important disadvantages of the slurry process. The purpose of this study is to propose a new suitable treatment method. This method consists of pretreatment of dye wastewater with ozonation, undertaking the immobilized-suspended photocatalytic process as the final treatment. In the immobilized-suspended photocatalytic process, nano TiO2 were coated on submerged media. The coated media was characterized by Scanning Electron Microscopy (SEM) and Energy- Dispersive X-ray microanalysis (EDX) techniques. The result has shown that COD removal efficiency decreased with a decrease in ozone injection rate, an increase in initial concentration, an increase in pH,a decrease in the number of media (nano TiO2 concentration) and a decrease in power of the light source. An experimental design, based on the Taguchi method, was applied to assess the effects of several operating parameters, including dye concentration, TiO2 concentration, pH, light source power, and ozone injection rate, on the energy consumption of the treatment. Based on experimental design data, optimum conditions were achieved at 50 mg/L of initial dye concentration, pH of 3, ozone injection rate at 1.2 gram per hour, 128 mg/L of nano $TiO_2$ (media number equal to 30) and 120 Watt UV-A light source. Under these conditions, dye removal was completed after 135 minutes. Then, in the photocatalytic process, 89% of COD was removed over 4 days using 30 media (128 mg/L), with 120 Watt light source.