Textile dye degradation technologies with mechanistic insights, kinetic modeling, and comparative performance analysis

Pollution caused by textile dyes constitutes a significant environmental challenge in the global textile industry, with over 280,000 tonnes of synthetic dyes discharged annually. Conventional treatment systems are effective at decolorizing wastewater; however, they fail to mineralize chromophores or eliminate the toxicity of the transformation products, raising concerns regarding regulatory compliance and public health. This review presents a mechanistic, kinetic, and comparative study of dye degradation technologies, combining molecular-level pathway information with quantitative kinetic modeling frameworks and multi-criteria technology evaluation. The key finding was (i) Anaerobic azo bond cleavage by azoreductase (EC 1.7.1.6) produces aromatic amines, many exhibiting greater mutagenicity than the parent dye as evidence by Ames testing, necessitating metabolite profiling via GC–MS and LC–MS. The Haldane substrate-inhibition model (μ = μmax·S/(Ks + S + S 2 /Ki)) is able to describe the nonlinear kinetics of the azo dye-degrading systems, with the BMG (Behnajady–Modirshahla–Ghanbery) kinetic model showing better fitting for photocatalytic decolorization than simple pseudo-first-order expressions. The efficiency of hydroxyl radicals was significantly reduced, and the rates of biological degradation were modified by (iii) water matrix components, such as Cl − (10–100 mM), SO 4 2− , humic acid (5–20 mg/L), and non-ionic surfactants. (iv) EPR spin-trapping experiments confirmed that ·OH, SO 4 ·, and O 2 · are the major reactive species in AOP-based systems, with TBA, p-BQ, and EDTA-2Na being used to validate the results of the experiments. The decolorization of effluents was 90–99% under visible-light irradiation using photocatalysts based on nanoparticles, MOFs, and COFs, and toxicity bioassays (Ames test, Daphnia magna EC50, zebrafish embryo FET) showed that the effluents were not mineralized but remained mutagenic after AOP treatment. Hybrid sequential anaerobic–aerobic systems and bio-AOP integration provide TOC removals of 85–97%, which is better than single-technology systems. This review is unique in bringing together mechanistic pathway analysis for four dye structural classes (azo, anthraquinone, triarylmethane, and phthalocyanine), quantitative kinetic modeling (including the BMG model), water matrix interference analysis, EPR-validated radical speciation, and toxicological bioassay requirements in a single comparative framework—addressing critical knowledge gaps not covered by existing reviews.