Wet oxidation of bleach plant effluent: Effects of pH on the oxidation with or without a Pd/Al2O3 catalyst

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Abstract
Wet oxidation of acidic bleach plant effluent was carried out at 423K and 1.5 MPa in a slurry reactor. The influence of pH of the bleach plant effluent was evaluated for both catalytic and non‐catalytic oxidation in the liquid phase. The stability of the heterogeneous catalysts was investigated by measuring the extent of metal leaching into the solution. The pH of wastewater solution was found to influence significantly both the rate of total organic carbon (TOC) removal and the stability of the Pd/Al2O3 catalyst. Leaching of palladium and alumina occurred mostly at pH 2 and pH 11 under experimental conditions. With Pd/Al2O3, comparable rates of TOC removal were obtained in the pH range of 5 to 9 without significant leaching of both palladium and alumina. No metal leaching was observed using the Pd‐Pt/Al2O3 catalyst at an initial pH value of 7. Implications of these experimental results for designing a catalytic wet oxidation process are discussed. A novel approach has been proposed for the treatment of effluents from softwood Kraft pulp mills.