Evaluation of UV/H2O2 advanced oxidation process (AOP) for the degradation of acid orange7 and basic violet 14 dye in aqueous solution

I. Introduction Extensive usage of dyestuffs and its disposal are the important sources for the today's environmental contamination. Different types of chemical and physical processes such as chemical coagulation, activated carbon adsorption are used for pollutant removal in the textile industrial wastewater, but they just transfer contaminants from one phase to another that needs further and ultimate disposal eventually Many researchers have reported that non-biodegradable including azo dye can be mineralized successfully and completely by the AOPs are the processes that involve highly reactive species, specifically hydroxyl radicals (oxidation potential 2.8V). Among the several methods for generating hydroxyl radicals, combining UV and hydrogen peroxide (UV/H 2 O 2) is one of feasible AOPs for dye wastewater treatment. UV/H 2 O 2 process is able to destroy totally the chromophore structure of azo dyes and the reaction rate of azo dyes depends on the basic structure of the molecule and on the nature of auxiliary groups attached to the aromatic nuclei of dyes (Galindo and Kalt, 1999). UV irradiation in the presence of H 2 O 2 leads to complete decolorization and mineralization of sulphonated azo and anthraquinone dyes (Colonna et al., 1999). The mechanism of dye destruction in AOPs is based on the formation of a very reactive hydroxyl radical (OH) that, with an oxidation potential of 2.80 V (Legrini O et.al., 1997 and Kang SF et al., 1999), can oxidize a broad range of organic compounds. Such a process implies relatively simple reactions, such as UV photolysis of H 2 O 2. Furthermore, the UV/H 2 O 2 process has the additional advantage of preventing any sludge formation during the different stages of the treatment. It can be carried out under ambient conditions and may lead to complete mineralization of organic carbon into CO 2 (Galindo C, et al., 1999). In spite of all its intrinsic advantages, to render AOP competitive with other processes, it is essential that its application represents a low cost operation, which basically implies a careful and continuous control of H 2 O 2 concentration. II. Experimental A. Materials The Acid orange 7 (AO7) and Basic violet 14 (BV14) are commercially available dyes and used without further purification. (Fig.1 & Table.1) The hydrogen peroxide solution (30%) of analytical grade, NaOH with 95% concentration, and HNO 3 with 70% concentration were used for reaction and to adjust the desired initial pH values of reaction mixtures.