Citric acid enhanced oxytetracycline degradation by Fe(Ⅲ)/peracetic acid: Performance, mechanism and influence factors

Abstract

Citric acid (CA) can effectively complex with Fe(Ⅲ) to improve the solubility of Fe(Ⅲ) and accelerate the reduction of Fe(Ⅲ) to Fe(II), while its use in Fe(Ⅲ)-activated peracetic acid (PAA) system has not been reported so far. Therefore, CA was introduced into Fe(Ⅲ)/PAA system in this study to degrade oxytetracycline (OTC), and the degradation efficiency and mechanism of OTC in this system were systematically investigated. The results showed that the removal efficiency of OTC in Fe(Ⅲ)-CA/PAA system at pH 7.0 could reach 81.5% after 20 min, and the degradation of OTC followed pseudo-first-order kinetic. The addition of CA into Fe(Ⅲ)/PAA system could effectively reduce Fe(Ⅲ) to Fe(Ⅱ) driving the cycle of Fe(Ⅲ)/Fe(Ⅱ) and accordingly enhance the OTC removal in this system. According to the results of electron paramagnetic resonance (EPR) and scavenging experiments, hydroxyl radical (HO•) and organic radicals (CH3C(O)O• and CH3C(O)OO•) played major roles for the degradation of OTC in Fe(Ⅲ)-CA/PAA system. Four possible transformation paths of OTC in this system were proposed, including demethylation, hydroxylation, dehydrogenation and dehydration, based on five detected degradation products. This study provides an idea to improve PAA activation by Fe(Ⅲ) and broadens the practical application of Fe(Ⅲ) in advanced oxidation processes.