The Study Of US/O₃ Technology

In the present work, the degradation efficiency and mechanism of mineralization of p-Nitrotoluene (PNT), m-Nitrotoluene (MNT) and C.I. Reactive Yellow 84 (RY84) in aqueous solution were investigated in laboratory-scale experiments in which pH, initial concentration, Ozone (O₃) dose, temperature and the energy density of ultrasound (US) were varied using sonolytic ozonation (US/O₃ oxidation).The degradation of PNT and MNT followed pseudo-first-order kinetics. The maximum degradation was observed at pH 10.0. As the initial concentration decreased, the degradation rate increased. Both temperature and O₃ dose had a positive effect on degradation. Of the total organic carbon (TOC) reduction, 8%, 68% and 85% were observed with US, O₃ and a combination of US and O₃ in PNT solution, while 41%, 9% and 56% were observed in MNT solution, respectively, proving that ozonation combined with sonolysis for removal of TOC is more efficient than ozonation alone or ultrasonic irradiation alone. The acute toxicity of MNT solution was also investigated, proving good performance on degradation when using US/O₃ oxidation. With by-products detected by gas chromatography coupled with mass spectrometry (GC/MS), possible reaction pathways for the decomposition of PNT and MNT in the US/O₃ process are proposed.The operational parameters and mechanism of mineralization of C.I. Reactive Yellow 84 (RY84), one of the azo dyes, in aqueous solution were investigated using sonolytic ozonation (US/O₃ oxidation). Of the pseudo-first- order degradation rate constants of TOC reduction, 9.0×10^-4 min^-1, 7.3×10^-3 min^-1, and 1.8×10^-2 min^-1 were observed with US, O₃ and a combination of US and O₃, respectively. These results illustrate that ozonation combined with sonolysis for removal of TOC is more efficient than ozonation alone or ultrasonic irradiation alone. With the initial pH value at 10.0, the ozone dose at 4.5 g/h, the energy density of ultrasound at 176 W/L, and the initial concentration of RY84 at 100 mg/L, the extent of mineralization measured as TOC loss was maximized. The variation of the concentrations of related ions (oxalate, formate, acetate, NO₃^-, NO₂^-, NH₄⁺, Cl^- and SO₄^2-) during the reaction process was monitored. Other organic intermediates were detected by GC/MS. Based on these findings, a tentative degradation pathway was proposed.