| Wastewaters generated as byproducts of dyeing processes are not treatable with conventional methods. It has been estimated that among the 900,000 tons of different dyes produced annually in the world, approximately 10--15% are lost in wastewater streams during manufacturing and processing operations. Once in rivers and streams, dyes cause major problems, such as reducing light penetration, or displaying toxic effects on aquatic life. Therefore, it is essential that dyes are removed from wastewaters before being discharged into the environment.;This study focuses on the catalytic wet air oxidation (CWAO) of Orange II, a mono azo dye used in large amounts in the United States. Seven metal-based heterogeneous catalysts, CuO/ZnO, CuO/Al2O3, Cu 2Cr2O5, Pt/SnO2/CeO2, CuO/CeO 2/Al2O3, MnO2/CeO2, and MnO2/CuO were screened for their efficiency in removing Orange-II dye from synthetically prepared wastewaters in a batch autoclave reactor. CuO/Al2O3 was selected as the best alternative catalyst based on TOC and Orange II removal efficiency, catalyst stability, and economic considerations. Kinetics experiments with CuO/Al2O3 revealed that the oxidation reaction proceeds very fast initially, with about 70% reduction in TOC concentrations within the first 10 minutes of reaction time. The overall TOC and Orange II removals increased with increased temperature up to reaction temperatures of 80°C. The reaction was found to be oxygen concentration limited. A lumped-parameter kinetic model was constructed to describe the reaction kinetics. The reaction rate constants were computed with non-linear regression. There was excellent agreement between experimental values and model computed values. The effects of catalyst concentration and pH on Orange II removal were also investigated. It was observed that lower pH values increased TOC removal. |
