Abstract

High-frequency ultrasound-assisted activation of peracetic acid (PAA) was investigated as a tunable advanced oxidation process for the removal of organic pollutants from water. Sunset Yellow FCF (SSY), a representative anionic azo dye, was used as a probe contaminant in a 425 kHz sonoreactor to clarify the roles of PAA speciation, acoustic cavitation, dissolved gases, oxidant dose, acoustic power, and initial pH. UV spectroscopic analysis showed that PAA exhibits pH-dependent far-UV absorbance associated with acid-base speciation and peroxide equilibria, while ultrasonication promoted simultaneous PAA activation and H2O2 accumulation. Compared with PAA alone and ultrasound alone, the combined US/PAA process markedly enhanced SSY decolorization. Under natural conditions, 5 mg/L SSY and 5 mM PAA were completely decolorized within 210 min, with an initial rate of 0.116 mg/L·min, compared with 0.078 and 0.0086 mg/L·min for ultrasound and PAA alone, respectively. The corresponding synergy ratio and synergy index were 1.5 and 1.34. The process exhibited tunable reaction-pathway control, with two favorable pH windows: a strongly acidic region, where interfacial HO•-driven sonochemistry and PAA stability are favored, and a mildly alkaline region, where PAA deprotonation promotes peracetate-driven acyl/peroxyl radical-chain propagation. Oxygen saturation improved performance, whereas CO2 suppressed cavitation-driven activation. Increasing PAA concentration and acoustic power enhanced removal up to practical limits, beyond which radical scavenging and diminishing sonochemical returns became evident. Beyond demonstrating enhanced decolorization, this study distinguishes US/PAA from previously reported UV/PAA, transition-metal/PAA, and ultrasound-only systems by showing how 425 kHz cavitation converts PAA into a tunable hybrid HO•/acyl–peroxyl radical network. The main contribution is a mechanistic operating map that links PAA speciation, sonochemical peroxide accumulation, dissolved gas chemistry, acoustic power, oxidant dose, and pH to pollutant-removal performance, thereby defining practical windows for sono-activated PAA treatment of anionic dyes and related recalcitrant contaminants.

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