Kinetics of the reaction between ozone and phenolic acids present in agro-industrial wastewaters

The kinetics of the ozonation of three phenolic acids is investigated from ozone absorption experiments in a semi-continuous reactor. After the evalua tion of stoichiometric ratios for the individual reactions between ozone an d each phenolic acid, the oxidation of p-hydroxybenzoic acid by ozone is pe rformed in a first stage. The influence of the operating variables on the d egradation process is established, and the application of a mass transfer w ith chemical reaction model based on the film theory leads to the determina tion of the reaction orders and kinetic rate constants. The experimental ab sorption rates obtained agree well with those calculated theoretically. In the second stage, a mixture of ferulic acid (4-hydroxy-3-methoxycinnamic ac id), beta -resorcylic acid (2,3-dihydroxybenzoic acid) and p-hydroxybenzoic acid is ozonated under different experimental conditions. The kinetic stud y is performed by means of a competitive method that takes p-hydroxybenzoic acid as reference compound. The application of this model allows to determ ine the kinetic rate constants for each compound, which are correlated as a function of pH and temperature. The results obtained support that the kine tic regime of absorption is fast and pseudo-first order with respect to ozo ne, a condition required by the competitive method used. (C) 2001 Elsevier Science Ltd. All rights reserved.