Traitement des eaux usées industrielles : Dégradation des colorants azoïques par un procédé intégré couplant un procédé d’oxydation avancée et un traitement biologique.

Abstract

This study aimed to investigate the removal of azo dyes from textile and tannery wastewater by an Advanced Oxidation Process (AOP) with a conventional biological treatment. The photocatalytic process using TiO₂ immobilized on nonwoven cellulose was applied as a pretreatment under three irradiation systems: UV/TiO₂, near-solar visible/TiO₂, and visible/TiO₂. The objective was to transform toxic azo dyes into less harmful and more biodegradable compounds before biological treatment with Pseudomonas fluorescens and activated sludge. The results demonstrated that photocatalysis is highly effective for the decolorization and mineralization of azo dyes, particularly under UV irradiation, due to the formation of highly reactive hydroxyl radicals (•OH). Dyes containing sulfonate groups degraded faster than those without such groups. Although complete decolorization was achieved, mineralization occurred more slowly because aromatic intermediates required additional time for complete degradation. Biological tests showed that untreated azo dyes were not biodegradable. However, photocatalytic pretreatment reduced their toxicity and improved their biodegradability. Among the biological methods tested, activated sludge showed better degradation performance than Pseudomonas fluorescens, achieving greater reductions in color, Chemical Oxygen Demand (COD), and Total Organic Carbon (TOC). Overall, the study confirms that coupling photocatalysis with biological treatment is an efficient and environmentally friendly approach for treating wastewater contaminated with azo dyes. The photocatalytic step reduces toxicity and enhances biodegradability, while the biological process completes the removal of the remaining organic pollutants, resulting in improved wastewater purification.