Supported noble metal catalysts in the catalytic wet air oxidation of industrial wastewaters and sewage sludges

Abstract

This paper reviews some catalytic wet air oxidation (CWAO) investigations of industrial wastewaters over platinum and ruthenium catalysts supported on TiO₂ and ZrO₂ formulated to be active and resistant to leaching, with particular focus on the stability of the catalyst. Catalyst recycling experiments were performed in batch reactors and long‐term stability tests were conducted in trickle‐bed reactors. The catalyst did not leach upon treatment of Kraft bleaching plant and olive oil mill effluents, and could be either recycled or used for long periods of time in continuous reactors. Conversely, these catalysts were rapidly leached when used to treat effluents from the production of polymeric membranes containing N,N‐dimethylformamide. The intermediate formation of amines, such as dimethylamine and methylamine with a high complexing capacity for the metal, was shown to be responsible for the metal leaching. These heterogeneous catalysts also deactivated upon CWAO of sewage sludges due to the adsorption of the solid organic matter. Pre‐sonication of the sludge to disintegrate the flocs and improve solubility was inefficient.

Keywords:

• catalytic wet air oxidation (CWAO)
• noble metal supported catalysts
• stability

Acknowledgements

These studies have been carried out with financial support from Région Rhône‐Alpes, European Commission (contract ICA3‐2002‐10096 Cat‐Med and 018525 Removals), Tredi and the Axelera International Competiveness Cluster.