O3+MnOx/GAC+H2O2 treatment: a novel strategy for simultaneous removal of TOC and AOX from high salinity dye wastewater

The dye manufacturing industry is an economically influential and thriving industry, and its wastewater pollution has attracted increasing attention. Catalytic ozonation is commonly employed in dye wastewater treatment for total organic carbon (TOC) removal. However, it remains a challenge to reduce the formation of adsorbable organic halogens (AOX) during the oxidation process in high salinity dye wastewater. To tackle this issue, we developed an innovative O₃+MnOx/GAC+H₂O₂ treatment method. After operation optimizing, the removal efficiency of TOC and AOX in dye wastewater surpassed 70% and 80%, respectively. The potential oxidation mechanism was examined through kinetic models, free radical detection, and scavenging experiments. The findings indicate that the presence of MnOx/GAC will catalyze O₃ to produce hydroxyl and superoxide radicals, and promote the conversion of halide ions to reactive halogen species (RHS). H₂O₂ supplementation can accelerate ozone decomposition, while modulating halogen species transformation pathways. Specifically, it changed ClO⁻/ClO₃⁻ into Cl⁻/ClO₂, simultaneously suppressing the formation of ClO₄⁻. H₂O₂ can also reduce bromine radicals and hypobromite back to bromide ions, effectively blocking bromate and bromite generation. Due to the shortened lifespan of O₃ and the quenching of RHS/HCl/HOBr by H₂O₂, there are fewer AOX by-products, chlorates and bromates generated during catalytic ozonation. Toxicity assessment of luminescent bacteria, chlorella and zebrafish eggs confirmed the superior detoxification performance of the integrated O₃+MnOx/GAC+H₂O₂ treatment system. This study proposes an innovative dual-functional approach for dye wastewater treatment, achieving concurrent organic mineralization and halogen elimination in high salinity wastewater.