Author(s)

A. Pintar, J. Batista & T. Tišler

Abstract

One of the most promising options for removal of toxic and non-biodegradable organic compounds from industrial wastewaters is destruction of these contaminants by means of catalytic wet-air oxidation (CWAO). In this study, the performance of various Ru/TiO2 catalysts to promote oxidation of aqueous solutions of formic acid, acetic acid and phenol was investigated in a continuousflow trickle-bed reactor. Oxidation experiments were carried out at T=328-523 K and total pressures up to 50 bar. Complete oxidation of formic acid was obtained at mild operating conditions (383 K), and no catalyst deactivation occurred that could be attributed to the dissolution of active ingredient material. Liquid-phase oxidation of recalcitrant acetic acid was found to be structure sensitive; the highest catalyst activity was obtained when the Ru phase on the catalyst surface prevailed in the zero-valent oxidation state. The employed Ru/TiO2 catalysts enable complete removal of phenol and more than 99% removal of TOC at temperatures above 483 K; at these conditions, no carbonaceous deposits were accumulated on the catalyst surface. In the presence of a Ru/TiO2 catalyst in the trickle-bed reactor, the toxicity to Daphnia magna and Vibrio fischeri of the oxidized materials was greatly reduced compared with that of the starting solutions. However, despite the notable decrease in toxicity, end-product solutions are generally more toxic than indicated by the concentrations of total organic carbon remaining in the final solutions. Keywords: acute toxicity tests, catalytic wet-air oxidation, heterogeneous catalysis, ruthenium catalysts, titanium oxide, trickle-bed reactor, wastewater treatment.

Keywords

acute toxicity tests, catalytic wet-air oxidation, heterogeneous catalysis, ruthenium catalysts, titanium oxide, trickle-bed reactor, wastewater treatment.