Enhanced humic acid degradation by Fe3O4/ultrasound-activated peroxymonosulfate : Synergy index, non-radical effect and mechanism

•The complete removal of humic acid was obtained by Fe3O4/US/PMS system in 20 min.•The synergy index of US for HA removal was calculated as 18.9.•The non-thermal effect of US played a main role in HA removal.•Non-radical 1O2 was the main contributor for HA removal in the Fe3O4/US/PMS system. In this study, Fe3O4/ultrasound (US) activated-peroxymonosulfate (PMS) was employed to degrade humic acid (HA). Magnetic nano-scale Fe3O4 particles were prepared via a co-precipitation method. The physical and chemical properties of Fe3O4 were characterized explicitly by a variety of methods, including scanning electron microscope-energy dispersive spectrometer (SEM-EDS), transmission electron microscope (TEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), Zeta potential, Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), and vibrating-sample-magnetometer (VSM). The synergy index of US and Fe3O4 activated PMS for humic acid degradation was calculated. After 20 min of reaction under the Fe3O4/Ultrasound/PMS system, 10 mg/L of HA solution was completely degraded. Batch experiments were conducted to determine the effect of PMS concentration, HA concentration, dosage of Fe3O4, and pH value on the degradation of HA in the absence and presence of US. The thermal and non-thermal effects of US on HA degradation were studied. Electron paramagnetic resonance (EPR) and quenching tests indicated that non-radical singlet oxygen (1O2) is the dominant contributor for HA degradation. This study provides a fast and cost-effective method for HA removal.