Removal of organic contaminants in paper pulp treatment effluents by TiO₂photocatalyzed oxidation

TiO2 slurries under UV light irradiation were used for the oxidation and removal of the organic load of effluent from the bleaching of paper pulp. TOC was the main analytical parameter used to characterize the reaction progress, although COD, AOX and color also received periodic attention. Conditions such as the catalyst load, light intensity, pH, temperature, and concentration of O2 and organic matter were changed through several series of experiments in order to determine their effect. A zero order kinetics accounts for the observed variation of TOC with time during most of the reaction, the rate constant being 0.25-0.40 ppm min-1 at 25 °C. This behavior is explained in terms of a Langmuir-Hinshelwood rate equation in a highly substrate concentrated system.