Ultrasonic activation of persulfate for removal of aqueous pollutants: cavitational versus thermal mechanisms

Abstract

Sulfate radicals have been extensively studied for application in advanced oxidation processes owing to their excellent oxidizing power and efficacy. Recently, ultrasound (US) technology has emerged as a promising method for activating persulfate (PS). This work provides a critical review of the removal efficiencies and pseudo-1st-order degradation rates in only-PS, only-US, and US/PS processes to clarify the ultrasonic activation mechanism in US/PS systems. Experimental data from 53 cases across 15 studies were analyzed, and synergistic effects were evaluated. In only-PS processes, significant activation below 40°C was rarely observed, with few exceptions. Although several researchers reported high synergistic effects in US/PS processes, most cases showed low or negligible synergistic effects. High synergistic effects were attributable to incomplete cooling systems, low pollutant concentrations, and high PS/pollutant ratios. Therefore, the ability of acoustic cavitation to activate PS without thermal activation induced by US attenuation below 40°C remains debatable.