Performances of soluble metallic salts in the catalytic wet air oxidation of sewage sludge

Various soluble transition metal salts were compared in the wet air oxidation of industrial and municipal sewage sludges (2.5–25 g L−1 total organic carbon) at 200–250 °C under 4–15 bar O2 partial pressure. The evolution of the TOC content in both the liquid and solid phases, and the overall TOC conversion were monitored. While copper sulphate prevented the dissolution of the suspended organic matter due to strong bounding of copper to a fraction of the organic matter in sludge, and showed high activity in the mineralization of the solubilized organic compounds (liquid phase), the implementation of iron sulphate resulted in a higher transfer of the organic matter to the liquid phase but in a moderate activity in the oxidation of solubilized molecules. When used in combination, a synergetic effect between these two salts was evidenced.