Electro-Catalytic Ozonation for the Treatment of Olive Mill Wastewater: Process Evaluation and Degradation Pathways

• Fe²⁺-mediated ECO achieved ≥96 % COD removal in 30 min. • ECO performed consistently across pH 2–9 without pre-conditioning. • Optimal current (175–200 mA) balanced radical generation and energy efficiency. • In-situ Fe²⁺ sustained •OH production despite ozone transfer limitations. • GC-MS revealed aromatic intermediates defining Fe²⁺–O₃ reaction pathways. Electro-catalytic ozonation (ECO) couples electrochemical Fe²⁺ generation with ozone oxidation to enhance radical-driven degradation of refractory organics. Here, ECO was evaluated for phenol and vanillin as model phenolic contaminants representing olive mill wastewater (OMW). Under optimized conditions (pH 5–9, 175–200 mA, ozone 3.6–5.3 g/hr), ECO achieved > 90 % COD removal and complete pollutant elimination via GC-MS verification within 30 min. Mechanistic analysis indicates a dual Fe²⁺–O₃ radical pathway that sustains •OH formation despite ozone mass-transfer limits. GC–MS confirmed complete parent compound loss with minimal stable aromatic intermediates, highlighting partially mineralized products. These findings clarify how electrochemical iron activation enhances ozone-based AOPs and define design parameters for hybrid treatment of phenolic wastewater.