Effects of catalysts during ozonation of salicylic acid, peptides and humic substances in aqueous solution

The oxidation of two model molecules (salicylic acid and a peptide) and humic substances in aqueous solution was studied using ozone in the presence of various catalysts. Experiments were performed in reactors operated either in batch (TOCo = 2.5 mg C.L-1) or in semi-continuous flow mode (TOCo = 42 mg C.L-1). The efficacy of the catalysts for TOC removal was shown to depend on the molecule in solution. Batch experiments indicated that for an applied ozone dose of 6.5 mg O-3.L-1, a clear improvement in TOC removal from humic substances and salicylic acid was observed with the attapulgite based catalyst. The alumina supported catalyst was the most efficient for the peptide solution. Additionally, the semi-continuous experiments carried out with salicylic acid confirmed that TOC adsorption on the attapulgite based catalyst was very low thus demonstrating that the improvement in TOC removal observed during ozonation in the presence of this catalyst is associated with mineralization. Furthermore, tests carried out with the alumina supported metal showed that the catalytic activity was sustained over an extended period of use for the highest ozone dose applied (5.4 mg O-3/mg TOCo).