Evolution of Toxicity upon Wet Catalytic Oxidation of Phenol

Abstract

This work reports on the evolution of the toxicity of phenol-containing simulated wastewater upon catalytic wet oxidation with a commercial copper-based catalyst (Engelhard Cu-0203T). The results of the study show that this catalyst enhances detoxification, in addition to its effect on the oxidation rate. The EC50 values of the intermediates identified throughout the oxidation route of phenol have been determined and used to predict the evolution of toxicity upon oxidation. The predicted values have been compared with the ones measured directly from the aqueous solution during the oxidation process. To learn about the evolution of toxicity through out the routes of phenol oxidation, experiments have been performed with simulated wastewaters containing separately phenol, catechol, and hydroquinone as original pollutants. The significant increase of toxicity observed during the early stages of phenol oxidation is not directly related to the development of the brown color that derives mainly from catechol oxidation. This increase of toxicity is caused by the formation of hydroquinone and p-benzoquinone as intermediates, the former showing the highest toxicity. Furthermore, synergistic effects, giving rise to a significant increase of toxicity, have been observed. These effects derive from the interactions among copper leached from the catalyst and catechol, hydroquinone, and p-benzoquinone and demand that close attention be paid to this potential problem in catalytic wet oxidation.

Carbon materials and catalytic wet air oxidation of organic pollutants in wastewater

“…Currently, the biodegradability of exiting CWAO streams was scarcely analysed. Santos et al [205] proposed the bioassay method using luminescent marine bacteria (photobacterium phosphoreum) for the toxicity determination of organic loaded wastewater samples. The tests are based on the 50% reduction of intensity of light emission measured after 15 min of contact time of the bacteria with the toxic compound.…”

Characterization and Activity of Cu/ZSM5 Catalysts for the Oxidation of Phenol with Hydrogen Peroxide

“…The main product among aromatics was catechol, followed by hydroquinone and benzoquinone, which exhibited the typical pattern for a series reaction scheme [24][25][26][27]. Since hydroquinone and benzoquinone are known to have higher ecotoxicity than phenol [28,29], it was important to completely remove these compounds, which took more than 3 h. The distribution of carboxylic acids, which also depended on the concentration of copper in the zeolite, is also shown in the Fig. 5.…”

Catalytic oxidation of phenol in wastewater — A new application of the amorphous Fe78Si9B13 alloy

“…Through HPLC analysis, before being degraded to small organic acids, phenol was first oxidized into various aromatic intermediates such as catechol, hydroquinone and benzoquinone, and then decomposed into CO 2 and H 2 O. According to Santos et al [41], hydroquinone and p-benzoquinone are 3 and 2 orders of magnitude more toxic than phenol, respectively, and catechol shows a toxicity value 2-fold that of phenol. Therefore, from an environmental point of view, the disappearance of phenol is still harmful to the environment and it must be oxidized completely into CO 2 and H 2 O.…”