Ultrasound-activated peracetic acid to degrade tetracycline hydrochloride: Efficiency and mechanism

The removal of pollutants by peracetic acid (PAA) has attracted much attention. However, such removal is not achievable solely by PAA without activation. This paper investigated the efficiency and mechanism of ultrasound-activated peracetic acid (US/PAA) to remove tetracycline hydrochloride (TCH). The results indicated that US/PAA process could successfully remove organic contaminants from water, and the degradation efficiency of TCH could reach 99.4% within 30 min. Adding ultrasonic radiation into the PAA solution could effectively activate PAA, and the US/PAA process increased the degradation efficiency of TCH by 4.88 times compared to the PAA process. The electron paramagnetic resonance (EPR) experiment and the radical quenching experiment both demonstrated that singlet oxygen (O-1(2)) and organic radicals (RO.) played an important role in the degradation of TCH during US/PAA process. The effects of the PAA dose, pH, ultrasound power, and initial TCH concentration on the removal of TCH in US/PAA process were investigated. The pH was the main factor, and the highest degradation efficiency was reached at a neutral pH (6.5-8.0). Additionally, the influence of water components (Cl-, HCO3-, SO42-, and humic acid) on the removal of TCH by US/PAA process was studied. The results showed that all water components inhibited the elimination of TCH, except 5 mmol/L HCO3-. Finally, the possible degradation products of TCH were identified by high performance liquid chromatography triple quadrupole mass spectrometer (HPLC-MS) analysis, and the potential degradation pathways mainly involved hydroxylation, demethylation, dehydration, and ring cleavage reaction.