Degradation of tetracycline by UV/Fe3+/persulfate process: Kinetics, mechanism, DBPs yield, toxicity evaluation and bacterial community analysis

As a widely produced and used antibiotic, tetracycline (TC) has been frequently found in rivers, soil and drinking water. In this study, the degradation of TC was investigated by UV/Fe3+/persulfate (PS) coupled process. The degradation behavior was well fitted with pseudo-first-order model. Hydroxyl radicals (·OH), sulfate radicals (SO4-·) and superoxide radical (O2-·) were identified as the primary reactive oxygen species (ROS) in UV/Fe3+/PS process, the contribution to TC degradation were found to be 41.94%, 33.94% and 17.44% at pH 3.0, respectively. Fe(IV) generated from the system also played a crucial role in TC removal. The effects of process parameters (PS/Fe3+ dosages, pH, humic acid, Cl-, HCO3-, NO3- and CO32-) on degradation were investigated. It was found that the degradation of TC was highly pH-dependent, and the optimal performance was obtained at pH 3.0. Except for Cl-, the presence of HA, HCO3-, NO3- and CO32- inhibited TC degradation. The possible transformation pathway involving the hydroxylation, N-demethylation, hydrogenation and dehydroxylation was proposed. Furthermore, the toxicity and mutagenicity of TC and transformation products (TPs) were estimated using ECOSAR and TEST softwares, demonstrating that the toxicity level of most TPs was lower/equal to their precursors. The evaluation of DBPs showed that UV/Fe3+/PS process could reduce the potential of DBPs formation, especially for TCAA and TCM. Microbial community composition was analyzed by 16 S rDNA sequencing, and the relative abundance of ARG-carrying opportunistic pathogens was significantly declined after UV/Fe3+/PS treatment. In general, this study provides an economical, efficient and safe strategy for TC removal.