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

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 x 10(-2) min(-1) was achieved in 120 min under the optimal conditions of cavitation number (Cv) 0.27, pH 5, molar ratio of oxidant to pollutant (rox) 8, ozone dose of 0.86 g h(-1) under 25 +/- 2 degrees C with initial concentration of 1,4-dioxane 100 ppm. The application of HC with SPC/O-3 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/O-3 was superior as compared to HC/H2O2/O-3, 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 center dot) radicals in the degradation of 1,4-dioxane among carbonate (CO3 center dot-) and superoxide (O-2(center dot-)) 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, Delta C-C splitting at the alpha-C position, subsequent dimerization, fragmentation and mineralization. Electric energy per order (EEO) for best process was 102.65 kWh center dot m(-3)center dot order(-1). Total cost of treatment was estimated as approx. 12 USD/m(3). 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.