SIMULATION DYNAMIQUE D’UN SYSTEME D'OXYDATION AVANCE POUR LE TRAITEMENT DES EAUX

Abstract

Textile effluents are typically treated through a physico-chemical process coupled with biological treatment. However, the quality of the resulting effluent does not always meet the required standards for recycling or discharge into nature. This is why advanced oxidation processes are used to eliminate remaining micropollutants. This study focuses on the degradation of the dye rhodamine B (RhB), used in the textile industry as well as in pharmaceutical and cosmetic industries, etc., through solar photolysis of hypochlorite ion. Consequently, reactive oxygen species (ROS) and reactive chlorine species (RCS), along with their involvement in the degradation process, are explored in this work through an in-depth kinetic modeling that allowed for the determination of rate constants for both radical and non-radical pathways of hypochlorite ClO-and the oxidation of RhB by free radicals. Using the software COPASI®, powered by a kinetic mechanism of 144 chemical reactions, the kinetic model of free radicals accurately fitted the experimental data under various conditions, including temperatures ranging from 25 to 55 °C, initial hypochlorite dosages varying from 300 to 1000 μM, and initial micropollutant concentrations from 10 to 25 μM, at a controlled pH of 11. The results indicate that an increase in hypochlorite dosages and temperatures enhances free radical concentrations and degradation rates of RhB. Conversely, an increase in pollutant concentration leads to a slowdown in its degradation. On the other hand, radicals •OH and ClO• were quantified as major contributors to RhB degradation, while ozone played a minor role. The model provides profiles for ROS and RCS, details on the distribution of radicals in RhB degradation, and predictions of rate constants for the photolysis of ClO-: kR1 = 2.67 × 10-4 s-1 for the radical pathway (ClO- + hν → O•- + Cl•), and kR2 = 1.88 × 10-5 s-1 as well as kR3 = 0 s-1 for non-radical pathways (i.e., ClO- + hν → O(3P) + Cl- and ClO-+ hν → O(1D) + Cl-, respectively). The rate constants for reactions of RhB with O•-, Cl•, Cl2•-, and ClO• were predicted to be 4.8 × 109 M-1 s-1, 1.45 × 109 M-1 s-1, 2.5 × 107 M-1 s-1, and 8.7 × 104 M-1 s-1, respectively. Lower rate constants were predicted for reactions of RhB with HOCl•-, HO2•, O2•- and O(3P), with values of 4.1 × 104 M-1 s-1, 7.3 × 105 M-1 s-1, 3.6 × 104 M-1 s-1, and 0.40 M-1 s-1, respectively.