Kinetic studies of the degradation of parabens in aqueous solution by ozone oxidation

摘要

Ozone degradation of a mixture containing methylparaben, ethylparaben, propylparaben, butylparaben and benzylparaben was carried out in aqueous solution. The degradation followed the pseudo-first-order kinetic model and occurs with two ozonation stages with the observed rate constants of second stage ozonation, k_(obs2), being higher than the observed rate constants in first stage, k_(obs1). The k_(obs1)of parabens was found to increase exponentially whilst k_(obs2) was found to maximize at 35°C. Both k_(obs1) and k_(obs2) were found to decrease exponentially with respect to the initial concentration of parabens. Both pH and ozone dose showed positive effects on the rate of degradation. It was also observed that an ozone dose of 0.67 g/h resulted in the removal of 99% of parabens in 12 min, and also the removal of 61 and 32% of chemical oxygen demand (COD) and total organic carbon (TOC), respectively, in 3 h of ozonation time for a 500 μM of solution of parabens.