Industrial wastewaters usually contain high concentrations of organic substances that have to be treated before being discharged into a municipal sewer system or the receiving water body. Different processes exist for the pretreatment of industrial wastewaters, depending on the composition and strength of the wastewater. Among the available pre-treatment technologies, catalytic wet air oxidation (CWAO) is a suitable technology for treatment of wastewaters containing high levels of refractory organic compounds that are not amenable to biological treatment, either as a complete treatment system by itself, or as a pre-treatment before biological treatment. Compared to conventional wet air oxidation, catalytic wet air oxidation offers lower energy requirements and much higher oxidation efficiencies. Effluents from dying baths in textile industry are one of the most problematic types of wastewater generated by the textile industry. These types of wastewaters have very strong color and high COD concentrations, and impose serious environmental problems, both in terms of treatment and aesthetic concerns. Orange II (also known as Acid Orange 7) is one of the dyes that are produced in large amounts in the United States. It is commonly used in pharmaceutical, food, and cosmetics industries as well as in the textile industry, and it is not amenable to conventional biological treatment. This paper discusses the selection of an efficient catalyst for the catalytic oxidation of Orange II. Different catalysts were tested for this study under different reaction conditions. The main reaction variables were temperature, oxygen pressure, dye concentration, stirring speed and catalyst loading. The experiments were conducted in a one-liter batch stainless steel autoclave reactor which is equipped with a stirrer, temperature and pressure controllers, gas introduction and vent lines, and a sampling port with a filter to filter out the catalyst and charred residue (if any) from collected samples. Half-factorial experimental design is utilized to screen the catalysts. Total Organic Carbon (TOC) reduction is used as the primary parameter to determine the treatment efficiency. Catalyst leaching and color reduction are also measured. The results will be discussed.

KEY WORDS: catalytic wet air oxidation, Orange II, azo dyes, textile wastewaters