Activated sodium percarbonate-ozone (SPC/O3) hybrid hydrodynamic cavitation system for advanced oxidation processes (AOPs) of 1,4-dioxane in water

Abstract

Hydrodynamic cavitation (HC) was employed to activate sodium percarbonate (SPC) and ozone (O₃) to degrade recalcitrant 1,4-dioxane. The degradation efficiency > 99 % with a rate constant of 4.04 × 10⁻² min⁻¹ was achieved in 120 min under the optimal conditions of cavitation number (C_v) 0.27, pH 5, molar ratio of oxidant to pollutant (r_ox) 8, ozone dose of 0.86 g h⁻¹ under 25 ± 2 °C with initial concentration of 1,4-dioxane 100 ppm. The application of HC with SPC/O₃ increased the degradation efficiency by 43.32 % in 120 min, confirming a synergistic effect between the coupled processes. In addition, the degradation efficiency of 1,4-dioxane in HC/SPC/O₃ was superior as compared to HC/H₂O₂/O₃, suggesting that the presence of SPC has a significant role in degradation of 1,4-dioxane. Radical quenching experiment revealed highest contribution of hydroxyl (HO) radicals in the degradation of 1,4-dioxane among carbonate (CO₃⁻) and superoxide (O₂⁻) radicals. The presence of co-existing anions resulted in an inhibitory effect in the following order: SO₄²⁻ > NO₃⁻ > Cl⁻. Based on GC–MS analysis, ethylene glycol diformate (EGDF) was detected as the main degradation product of 1,4-dioxane. The observed intermediate supports the radical route of 1,4-dioxane oxidation, which involves H-abstraction, ΔC-C splitting at the α-C position, subsequent dimerization, fragmentation and mineralization. Electric energy per order (E_EO) for best process was 102.65 kWh·m⁻³·order⁻¹. Total cost of treatment was estimated as approx. 12 USD/m³. These findings confirmed the SPC as an efficient, environmentally-friendly alternative to H₂O₂ and broadened the scope of HC-based AOPs for water and wastewater treatment.