Performance of heterogeneous catalytic ozonation with minerals in degradation of p-chlorobenzoic acid (p-CBA) from aqueous solutions

Water pollution is a critical environmental issue nowadays. One major problem is the pollution of freshwaters by contaminants of low concentrations (ng/L – μg/L), known as micropollutants. The most promising techniques for micropollutants degradation are the Advanced Oxidation Processes (AOPs). Heterogeneous catalytic ozonation is belonging among them and recent studies shown that can be an efficient water treatment technique. The aim of this study is to evaluate the catalytic activity of five minerals (anatase, dolomite, kaolin, talc and zeolite) on ozonation of small concentrations of p-CBA at pH 7 by batch mode experiments. p-CBA was employed as a model compound for the performance evaluation of single and catalytic ozonation, because it cannot be efficiently removed by direct ozonation (k_O3 < 0.15 M^-1s^-1), while having high reactivity with hydroxyl radicals (k_•OH = 5*10⁹ M^-1s^-1). It was found that all applied solid materials can be characterized as catalysts, except kaolin, whose use presented almost the same performance as single ozonation. The best results were obtained by zeolite and dolomite (> 99.4%) within 15 min reaction/oxidation time. These materials were neutral (PZC = 6.8) and positive (PZC = 10.1) charged respectively, during the oxidation process (pH 7) favoring the contact of micropollutant and ozone with the catalysts’ surface. On the other hand the addition of anatase and talc in the ozonation system resulted in 97.5% and 98.5% p-CBA degradation respectively, due to their slightly negative charge throughout the reaction. Conclusively, the experimental results indicated that the performance of heterogeneous catalytic ozonation is strongly depending on the surface charge of the solid materials (catalysts).