Abstract
Heavy metal pollution has been a focus with increasing attention, especially Pb2+, Cd2+, and Ni2+ in an aqueous environment. The adsorption capacity and mechanism of extracellular polymeric substances (EPS) from Agrobacterium tumefaciens F2 for three heavy metals were investigated in this study. The adsorption efficiency of 94.67%, 94.41%, and 77.95% were achieved for Pb2+, Cd2+, and Ni2+ adsorption on EPS, respectively. The experimental data of adsorption could be well fitted by Langmuir, Freundlich, Dubinin–Radushkevich isotherm models, and pseudo-second-order kinetic model. Model parameters analysis demonstrated the great adsorption efficiency of EPS, especially for Pb2+, and chemisorption was the rate-limiting step during the adsorption process. The functional groups of C=O of carboxyl and C-O-C from sugar derivatives in EPS played the major role in the adsorption process judged by FTIR. In addition, 3D-EEM spectra indicated that tyrosine also assisted EPS adsorption for three heavy metals. But EPS from strain F2 used the almost identical adsorption mechanism for three kinds of divalent ions of heavy metals, so the adsorption efficiency difference of Pb2+, Cd2+, and Ni2+ on EPS could be correlated to the inherent characteristics of each heavy metal. This study gave the evidence that EPS has a great application potential as a bioadsorbent in the treatment of heavy metals pollution.
Highlights
Heavy metal pollution mainly comes from papermaking, smelting, electroplating, and other industrial wastewater and the overuse of pesticide and fertilizer [1]
The adsorption efficiency difference of Pb2+, Cd2+, and Ni2+ on extracellular polymeric substances (EPS) could be correlated to the inherent characteristics of each heavy metals, which deserve an indepth investigation via a quantitative structure–activity relationship (QSAR)
The obvious changes in C=O of carboxyl and C-O-C bands from sugar derivatives via Fouriertransform infrared spectroscopy (FTIR) could support the viewpoint of that the polysaccharides as the main constituent in EPS played the key role during the adsorption process of Pb2+, Cd2+, and Ni2+ ions
Summary
Heavy metal pollution mainly comes from papermaking, smelting, electroplating, and other industrial wastewater and the overuse of pesticide and fertilizer [1]. The most commonly used treatment techniques for heavy metal pollution include chemical precipitation, ion exchange, adsorption, membrane separation, oxidation reduction, and electrochemical [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22] Among these methods, adsorption is preferred for its simplicity, efficiency, flexibility in design, low waste production, and environmental-friendly characteristics for certain biosorbents [23]. It was used to adsorb heavy metal contaminants, and the adsorption mechanisms were systematically investigated via qualitative and quantitative analyses, thereby providing a new available bioadsorbent in water treatment
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