Sonolysis and sono-Fenton oxidation for removal of ibuprofen in (waste) water

Two sonochemical processes were compared for the removal of ibuprofen in different water matrixes (distilled water and effluent from wastewater treatment plant). The effect of various operating parameters, such as pH (2.6-8.0), ultrasound power density (25-100 W/L), sonication frequency (12-862 kHz), addition of radical promoters (H2O2 and Fenton's reagent) or scavengers (n-butanol and acetic acid), was evaluated. Sono-degradation of ibuprofen followed a first-order kinetic trend, whose rate constant increased with ultrasound density and frequency. For this hydrophobic and low volatile molecule, a free-radical mechanism at the bubble interface was established. Coupling ultrasound with Fenton reaction showed a positive synergy, especially in terms of mineralization yield, while adding H2O2 alone had no significant beneficial effect. Dedicated experiments proved this synergy to be due to the enhanced regeneration of ferrous ions by ultrasound. Efficacy of the sonolysis process was hampered in wastewater matrix, mainly as the consequence of higher pH increasing the molecule solubility. However, after convenient acidification, sono-Fenton oxidation results remained almost unchanged, indicating no significant radical scavenging effects from the effluent compounds.