Monitoring the Sonochemical Degradation of Phenolics in Olive Oil Wastewater Using Co(ll)EDTA-Induced Luminol Chemiluminescence

Olive Mill Wastewater (OMW) poses significant environmental challenges due to its high phenolic content and associated toxicity. This study developed and optimized an ultrasound-based advanced oxidation process for phenolic degradation in OMW, utilizing Co(II)/EDTA-induced luminol chemiluminescence as a novel monitoring technique. Systematic investigation of operational parameters revealed optimal degradation conditions of 150 W power, 80 kHz frequency, 25°C temperature, and 5% NaCl concentration, achieving 15% phenolic reduction after 240 minutes. Temperature elevation above 25°C suppressed degradation due to vapor cushioning effects during cavitation collapse, while sodium chloride enhanced degradation through salting-out effects that intensified bubble implosion. The chemiluminescence method demonstrated strong correlation with Folin-Ciocalteu measurements (R² = 0.83 for two-phase OMW, R² = 0.64 for three-phase OMW), validating its utility for rapid antioxidant activity assessment. LC-MS analysis confirmed phenolic structure breakdown, with peak area reductions of 36% and 75% observed for two-phase and three-phase OMW, respectively. Statistical analysis established significant positive correlations between total phenolic content and antioxidant activity (r = 0.69–0.81), enabling direct toxicity assessment through chemiluminescence monitoring. These findings establish sonochemical treatment as a viable pre-treatment or polishing step within integrated OMW treatment trains, while the Co(II)/EDTA-luminol method provides a sensitive, reproducible tool for real-time monitoring of oxidative efficacy across diverse advanced oxidation configurations. The graphical abstract presents a four-step workflow reading from left to right. Step 1 shows two Erlenmeyer flasks containing 2-phase and 3-phase olive mill wastewater (OMW), representing the high-phenolic toxic feedstock. Step 2 depicts the sonochemical treatment setup with a titanium horn immersed in an OMW-filled glass vessel submerged in a 25 °C water bath, where 80 kHz/150 W ultrasound generates cavitation bubbles. Step 3 illustrates real-time monitoring via Co(II)/EDTA-induced luminol chemiluminescence, with luminol, Co(II)/EDTA, and H₂O₂ reagents producing a measurable CL signal. Step 4 summarizes the key results: 15% phenolic reduction, strong correlations between chemiluminescence and Folin-Ciocalteu measurements (R² = 0.83 for two-phase, 0.64 for three-phase), LC-MS confirmation of 36 to 75% peak area reduction, and validated pseudo-first-order degradation kinetics, culminating in reduced environmental toxicity and a validated monitoring method.