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 hum ic substances in aqueous solution was studied using ozone in the presence o f 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 mo lecule in solution. Batch experiments indicated that for an applied ozone d ose of 6.5 mg O-3.L-1, a clear improvement in TOC removal from humic substa nces and salicylic acid was observed with the attapulgite based catalyst. T he alumina supported catalyst was the most efficient for the peptide soluti on. Additionally, the semi-continuous experiments carried out with salicylic ac id 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 mineralizati on. Furthermore, tests carried out with the alumina supported metal showed that the catalytic activity was sustained over an extended period of use fo r the highest ozone dose applied (5.4 mg O-3/mg TOCo).