Contribution à l’étude de dégradation in situ d’un polluant organique par procédés d’oxydation avancés.

Abstract

ABSTRACT This thesis aims to study the efficiency of advanced oxidation processes (AOPs) based on periodate (IO₄⁻) activation for the removal of an azo dye, Acid Orange 10 (AO10) from aqueous solutions. Organic dyes represent a major source of pollution in industrial wastewater, particularly from the textile industry, necessitating the development of efficient and sustainable treatment techniques. In this context, three periodate activation strategies were explored: activation by hydrogen peroxide (H₂O₂/IO₄⁻), UV irradiation (UV/IO₄⁻), and zero-valent iron (Fe⁰/IO₄⁻), with the objective of identifying the most effective approach for dye degradation and optimizing oxidation process performance. The degradation of AO10 in the aqueous phase by the H₂O₂/IO₄— process is studied. The influence of several parameters was evaluated, including periodate and hydrogen peroxide concentrations, initial dye concentration, pH, temperature, the presence of methanol, inorganic salts, and different aqueous matrices. The results revealed no linear relationship between degradation efficiency and oxidant concentrations, as high H₂O₂ and IO₄⁻ concentrations led to a decrease in the formation of reactive oxidative species, particularly •OH, while high temperatures negatively affected the reaction. Additionally, dye removal was nearly complete under acidic conditions (pH ≤ 5.7), achieving over 97% efficiency at pH = 3, whereas it dropped to about 16% in neutral conditions and less than 10% at pH 8 and 10. Furthermore, high water salinity negatively impacted process efficiency, as confirmed by experiments conducted on seawater, natural mineral water, and river water. Optimization of operational parameters and understanding of variable effects were further enhanced through experimental modeling using the Box-Behnken design. For the photochemical degradation of AO10 in aqueous phase using photo-activated periodate (UV/IO₄⁻), the effects of operational parameters on dye degradation were investigated. The results indicated that periodate photodecomposition generates highly reactive oxidizing radicals (•OH, IO₃•, IO₄•), promoting AO10 degradation. However, high periodate concentrations (> 3 mM) slowed down the reaction due to interactions between oxidizing radicals. Moreover, the presence of salts, surfactants, and sucrose significantly inhibited dye removal. Specifically, sucrose addition reduced degradation efficiency, while tert-butanol, a known •OH radical scavenger, had no significant effect even at high concentrations, suggesting that the degradation mechanism in this system is not exclusively •OH-dependent. Furthermore, chemical oxygen demand (COD) analysis showed that the UV/IO₄⁻ system enabled partial mineralization of organic matter, achieving 56.5% and 60.5% COD reduction after 60 and 120 minutes, respectively, confirming its potential for treating industrial dye-laden effluents. The activation of periodate by zero-valent iron (Fe⁰/IO₄⁻) has been studied. The effects of various parameters, such as Fe⁰ concentration, periodate dose, initial pH, and temperature, were examined. The results highlighted that this system is particularly effective under acidic conditions (pH = 3), favoring the formation of oxidative species like •OH, IO₃•, and IO₄•. The impact of sucrose addition, inorganic salts (NaCl, Na₂SO₄), and surfactants (SDS, Tween 80, Triton X-100) was also assessed, revealing that these compounds can partially inhibit degradation by interfering with radical generation. Despite these effects, this system achieved nearly complete AO10 removal, reaching 99.5% degradation under optimal conditions, making it one of the most promising processes for the remediation of dye-polluted industrial wastewater. Keywords: advanced oxidation processes, azo dye, Acid Orange 10, dye degradation, wastewater treatment, UV/periodate, H₂O₂/IO₄ˉ, Fe⁰/IO₄ˉ.