RESUMO
Microplastic-derived dissolved organic matter(MPDOM) during the aging process could be complexed with organic pollutants, heavy metals, and other contaminants and thus affect their migration and transformation. In this study, two types of microplastics, polyethylene terephthalate(PET) and polystyrene(PS), were selected to investigate the spectral properties of MPDOM and their effect on the complexation between MPDOM and sulfadiazine(SDZ)/copper ion(Cu2+) using the fluorescence quenching method, various spectroscopic analysis techniques, and the Ryan-Weber quenching model. The results of UV-vis absorption spectroscopy analysis showed that the molecular weight of the two MPDOMs decreased; the aromaticity and humification increased; and the carboxyl, carbonyl, hydroxyl, and ester substituents on aromatic rings increased after aging. The fluorescence quenching process between MPDOM and SDZ/Cu2+ was static quenching. After quenching, the aromaticity and humification of the two MPDOMs were similar, and the molecular weights were comparable. Combined with three-dimensional fluorescence spectra and parallel factor analysis, two humic-like components and one protein-like component were identified. In addition, the protein-like components of MPDOM reacted preferentially with SDZ and were more sensitive to Cu2+. The results of the Ryan-Weber quenching model revealed that the binding ability of humic-like components to PET-DOM was higher in both SDZ and Cu2+ quenching systems, but the binding ability of MPDOM in the SDZ quenching system was generally stronger than that in the Cu2+ system.
RESUMO
Fe2+ has been commonly selected to activate peroxydisulfate(PDS) for sulfate radical(SO4-·) generation because of its eco-friendly, cost-effective, and high activity characteristics. However, Fe2+ can be rapidly oxidized to Fe3+ in the reaction, leading to poor utilization of iron for PDS activation. Further, a fairly high concentration of Fe2+ is generally required and may cause iron sludge production and secondary pollution. In this study, a minute Fe2+-activated PDS system induced by bisulfite(BS) was used to degrade paracetamol(APAP) in water. The results showed that the Fe2+-PDS system could be enhanced by the circulation of Fe2+-Fe3+ with the injection of BS and by keeping Fe2+ at a high concentration. Under the optimal conditions(PDS=0.6 mol·L-1; BS=0.4 mol·L-1; Fe2+=10 µmol·L-1; pH=4), 100% APAP(4 µmol·L-1) was removed within 180 s. The degradation rate of APAP increased with the increase in BS(0-0.6 mmol·L-1) and PDS(0.2-1.5 mmol·L-1) concentration, and a modest Fe2+ concentration could accelerate APAP removal. Co-existing substances inhibited the APAP removal and followed the order of HCO3->HPO42->Cl->NO3->humic acid(HA). Based on the quenching experiments and electron paramagnetic resonance spectroscopy test, SO4-· was shown to be the primary reactive species for APAP decomposition in the BS-Fe2+-PDS process. Three-dimensional fluorescence spectroscopy revealed that APAP intermediates had fluorescence characteristics. Moreover, five intermediates were identified, and the probable APAP degradation pathways were proposed. The removal efficiencies of APAP were lower in real waters than that in ultrapure water. Nevertheless, the removal effect was greatly improved after a prolonged reaction time. All results indicated that the BS-Fe2+-PDS system could be a promising method for organic pollutant treatment.