Degradation of acid red 73 wastewater by hydrodynamic cavitation combined with ozone and its mechanism.

Many azo dyes are consumed in the textile and dyeing industry, which makes the wastewater recalcitrant and toxic to the aquatic environment. Dye degradation by the combination of hydrodynamic cavitation and ozone (HC + O) has caused extensive interest. The degradation mechanism of the hybrid system needs further investigation. This study investigated the degradation of acid red 73 (AR73) by HC + O. Meanwhile, the degradation pathways and mechanisms were present. The optimal operation parameters were: inlet pressure of 0.15 MPa, O dosage of 45 mg/min, initial dye concentration of 10 mg/L, and initial pH at 7.5. As a result, the decolorization rate, removal of UV and NH-N were 100%, 71.28%, and 87.36% in 30 min, respectively. Humic acid and most of the co-existing anions (HCO, SO, Cl, PO, NO) played a positive role in the degradation of AR73, while NO restrained. The reactive species of singlet oxygen (O), hydroxyl radicals (·OH) and super oxygen radicals (·O) showed synergism in the hybrid system, and the decolorization was attributed to the fracture of azo bonds by O. Meanwhile, aromatic amines were generated and further degraded into small molecule compounds. The research certificated that the HC + O can be an effective technology for azo dye degradation.