| In this study, a novel ultrasound-enhanced heterogeneous Fe~0/persulfate(US/Fe~0/PS) system was developed and investigated for the degradation of an antibiotic sulfadiazine(SD). It was demonstrated that the US/Fe~0/PS system could achieve a significant synergy in the degradation efficiency of SD. The SD degradation in the US/Fe~0/PS system could be applied by the pseudo-first-order kinetic with a kobs(SD) value of 3.4 ± 0.20 h-1. Affecting factors such as initial p H, dosage ratio of [Fe~0]:[PS], US input power and reaction temperature were further studied. SD could be effectively degraded with a relatively low PS dosage at a broad p H range of 3.00-7.00. By using the response surface methodology, an optimized experimental condition of p H 7.00, 0.94 m M Fe~0, 1.90 m M persulfate(PS) and 20 W ultrasound(US) input power was concluded, which could reach the predicted SD degradation efficiency of 90%.Simultaneous evolution of soluble iron species and PS was evaluated in different comparative systems during the reaction. It could be concluded that the promotional role of US would be the enhancement in the heterogeneous iron corrosion reactions and acceleration in the bulk radical reactions. Identification of the degradation intermediates indicated that sulfate radical(SO4?-) oxidation was the main SD degradation pathway. Attacking of the amine group in the benzene ring would be its first step, followed by cleavage of C-N bonds in the heterocyclic ring. Another degradation pathway, i.e. direct cleavage of the S-N bond should be also present.Afterwards, effects of wastewater matrix(five inorganic anions and two chelating agents) on the SD degradation were investigated in the system, respectively. It was found that the SD degradation could be inhibited by SO42-, NO3-, HCO3-/CO32- and H2PO4-to different extents. Cl- would lead to an enhancement with a low dosage, but an inhibition with a high dosage. Unexpectedly, chlorinated organic intermediates were also found as SD decomposed. Appropriate dosages of oxalic acid or EDTA could benefit the SD degradation in the system, while excessive chelating agents would play as competitive pollutants. It was summarized that inorganic anions would mainly react with SO4?- and ?OH to form sub-radicals of less oxidative potential. Ox A and EDTA would not only participate in complexing dissolution of Fe~0 but also provide additional oxidants such as H2O2 and [FeIVO]2+, through the electron transfer reactions caused by the iron-ligands species.The effect of natural organic matter such as humic acid(HA) and fluvic acid(FA) on the SD degradation were also investigated for the US/Fe~0/PS system. It was found that SD could still be effectively degrade despite high concentrations of HA or FA presented. Characterizations of the realted water samples by high performace size-exclusion chromatography(HPSEC), fourier transform infrared(FTIR) and three-dimensional fluorescence spectra(3DEEM) suggested that the structure of organic macromolecules was destroyed into small molecules, with the direct oxidation of some functional groupse.g.-NH2. Application test of the system in treating RO concentrated water was also tried. The spiked SD in the RO concentrate could be efficiently decomposed with simultaneous destroy of the main trace organic component FA and HA. The removal efficiency was accelerated with increasing initial Fe~0/PS dosage. |
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