Advanced oxidation of ethylene and propylene glycol in wastewater using hydrodynamic cavitation-activated persulfate: a kinetic and techno-economic study

In this work, the activation of persulfate (PS) using a vortex diode-based hydrodynamic cavitation (HC) system for the degradation of ethylene glycol (EG) and propylene glycol (PG) in aqueous media was evaluated. Glycol degradation in a PS activated system was determined under varying glycol concentrations (100-1000 mg/L), PS-to-glycol molar ratios (0.06-3.04), and operating temperatures (25-55 °C). Degradation kinetics followed a first-order model, with the per-pass rate constant for PG at temperatures below 30 °C calculated at 2.7 × 10^-4 per pass, while EG showed negligible degradation under similar conditions. At elevated temperatures (> 55 °C), the rate constants increased to 6.02 × 10^-4 per pass for EG and 3.9 × 10^-4 per pass for PG, indicating the strong thermal enhancement synergistic with cavitational effects. HC/PS system demonstrated almost twofold higher cavitation yield and faster treatment time for 90% degradation compared to electrical heating/PS system. Complete degradation (> 90%) required a PS: glycol ratio greater than 4. The degradation intermediates identified included formic acid, acetic acid, propanoic acid, and hydroxy-acetaldehyde, suggesting sulfate and hydroxyl radical-driven pathways. Techno-economic analysis revealed that HC/PS used significantly less energy (233.4-645.9 kWh/m³) than electrical heating/PS (718.9-1043 kWh/m³), indicating its superior energy efficiency. The operational cost including oxidant costs for glycol degradation using HC/PS system was found to be 3.55 times more economical than conventional thermal activation, with a threefold reduction in treatment time (6 h vs. 18 h for 90% degradation). These findings establish HC as a scalable, energy-efficient, and cost-effective method for the oxidative treatment of glycol-rich wastewater streams.