Oxidation of resin and fatty acids by ozone: Kinetics and toxicity study

The ozonation of resin and fatty acids (RFAs) found in pulp mill effluents was investigated using rapid-scan stopped-flow spectrophotometry. RFAs oxidation (i.e., degradation) efficiency increased with increasing the amount of used ozone and temperature. The degradation process with respect to the acid was found to follow first-order kinetics. The ozonation of RFAs was modeled as an overall second-order reaction for both reactants. The apparent overall second-order rate constants were calculated based on the pseudo first-order rate constants obtained from the kinetic data fitting for the acid degradation. The apparent overall second-order rate constant was affected by pH and temperature. At 20 °C and when pH increased from 8 to 11, the apparent overall second-order rate constant increased almost by a factor of 5 (from 3.9×103 to 1.8×104 M−1 s−1) for 9 mg L−1 resin acid and a factor of 4 (from 9.6×103 to 3.9×104 M−1 s−1) for 8 mg L−1 fatty acid. At pH 8 and as temperature increased from 10 to 20 °C, the apparent overall second-order rate constant increased almost by a factor of 5 (from 8.2×102 to 3.9×103 M−1 s−1) for 9 mg L−1 resin acid and a factor of 3 (from 3.5×103 to 9.6×103 M−1 s−1) for 8 mg L−1 fatty acid. Microtox™ bioassay tests were completed to evaluate the toxicity of RFAs samples before and after ozonation. For the resin acid, there was an increase in toxicity as a result of ozonation. Meanwhile, toxicity of fatty acid samples decreased as a result of ozonation.