Dr. Valdes-Morales, Hector

Benzothiazoles are emerging chemical pollutants mainly coming from leather, paper and rubber industries; due to their use as: herbicides, corrosion inhibitors, anti-freezers, and vulcanisation accelerators. This article presents experimental data on ozone treatment of benzothiazole contaminated waters. The effect of the initial concentration of benzothiazole, ozone dosage, temperature (10-30 °C), and pH (2-9), on ozonation removal rate were assessed at bench scale. Experimental results show that reaction between ozone and benzothiazole could be approximated to a second-order kinetic law. Kinetic parameters for direct and indirect ozone reactions are estimated and temperature dependence of rate parameters is evaluated. Moreover, an initial degradation pathway of benzothiazole ozonation is proposed.

The influence of the variation of chemical surface properties of activated carbons on the sorption capacity of activated carbons used in hybrid heterogeneous ozonation systems is still under discussion. In this study, the effect of long exposure of activated carbon to ozone and its implication on the removal of emerging organic pollutants from waters is evaluated. A commercial activated carbon (Filtrasorb-400) is used here as a raw material. It is chemically modified by continuous ozone exposure. 2-hydroxybenzothiazole (OHBT) is chosen as a target organic contaminant, representative of emerging micro-pollutants. Results obtained here reveal that extensive exposition of activated carbon surface to ozone weakens adsorbate–adsorbent interactions. Highly exposed activated carbon to ozone increases the concentration of oxygen-containing acidic functional groups, leading to a higher concentration of surface electron-withdrawing groups such as carboxylic acid anhydrides and carboxylic acids and reducing the sorption capacity toward OHBT in the hybrid heterogeneous ozonation system. At pH conditions around the point of zero charge (pHPZC), such sorption reduction could be due to a decrease on dispersive interactions among π-electrons of aromatic ring of OHBT molecules and the π-electron system of carbon graphene layers, coming after extensive exposition of activated carbon surface to ozone. However, at pH >pHPZC low removal of OHBT is obtained because of the appearing of repulsive electrostatic interactions among the ionised form of OHBT molecules and the de-protonated form of oxygen-containing functional groups that appears after long contact with ozone. In addition, a new concept to predict activated carbon performances in a hybrid heterogeneous ozonation process is proposed.

Volatile organic compounds (VOCs) are responsible for damage to health due to their carcinogenic effects. Catalytic ozonation using zeolite appears as a valuable process to eliminate VOCs from industrial emissions at room temperature. For full-scale application of this new abatement technology, an intrinsic reaction rate equation is needed for an effective process design and scale-up. Results obtained here provide a mechanistic approach during the initial stage of catalytic ozonation of toluene using an acidic surface transformed natural zeolite. In particular, the contribution of Lewis and Brønsted acid sites on the surface reaction mechanism and overall kinetic rate are identified through experimental data. The least-squares non-linear regression method allows the rate-determining step to be established, following a Langmuir–Hinshelwood surface reaction approximation. Experimental evidence suggest that ozone is adsorbed and decomposed at Lewis acid sites, forming active atomic oxygen that leads to the oxidation of adsorbed toluene at Brønsted acid sites.