Advanced Oxidation via Hydrodynamic Cavitation and Ozonation for Enhanced Decolorization and Biodegradability of Triazo Dyes in Textile Wastewater

Textile wastewater containing azo dyes poses environmental and health risks if untreated. This study evaluated the decolorization of the azo dye Direct Blue 71 (DB71) using advanced oxidative processes (AOPs), specifically hydrodynamic cavitation (HC) and ozonation, both independently and in combination with biological treatments. HC as a pretreatment significantly improved DB71 biodegradability, achieving a 95.7% removal efficiency. Anaerobic batch tests showed that cavitation pretreatment doubled methane production (6.81 N mL-CH₄) compared to untreated wastewater (2.96 N mL-CH₄) and reduced dye removal time from 25 to 16 h. Thirteen central composite design experiments indicated organic carbon removal ranging from 7.6% to 58.3%, depending on the ozone flow rate (1.5-4.5 g-O₃ h^-1) and exposure time (30-100 min). Combining cavitation with 1 g-O₃ h^-1 fully removed DB71 and its byproducts in under 20 min, thanks to the synergistic effect of AOPs. These results demonstrate that combining HC with ozonation significantly enhances the oxidative degradation of recalcitrant azo dyes compared to individual processes. Moreover, the integration of AOPs with biological treatment provides a synergistic pathway that improves dye decolorization, increases biodegradability, and reduces the inhibitory effects of toxic intermediates, offering a potentially sustainable and promising strategy for textile wastewater remediation.