| Wastewater treatment with microbial resources is a safe and effective method, and the development of new microbial resources is of great significance. Exopolysaccharides (EPS) secreted by extremophiles show broad prospects in particular water treatment, because of their unique advantages. Pseudoalteromonas sp. Bsi20310 was isolated from Antarctic sea-ice, which could secrete a large amount of EPS at low temperature and high salinity. In this study, Bsi20310 EPS was prepared by bio-fermentation technology; its properties were studied using several methods; its enhancement on coagulation of reactive brilliant red X-3B (RX-3B) by ferric chloride was studied; and its adsorption for Pb(Ⅱ) from simulated seawater and freshwater was investigated.The main component of Bsi20310 EPS was neutral polysaccharide with the content about 52%, and the content of protein and nucleic acid was absent. The main elements of SM-A87 EPS were C, H, O, S and N. The temperature of thermal decomposition process were observed at 244℃. SEM image showed the surface of SM-A87 EPS was irregular multilayer micro-fibriform, which had high specific surface area about 1993.2 m2/g. The main functional groups are hydroxyl, carboxyl groups and glycosidic bond. Zeta potential of the EPS was negatively at neutral condition. The EPS showed pH buffer capacity.The enhancement of Bsi20310 EPS on decolorization of simulated RX-3B dye wastewater coagulated by FeCl3·6H2O was evaluated. Optimum initial solution pH, coagulant dosage, EPS dosage and EPS adding timing for RX-3B removal were determined and the possible mechanisms of Bsi20310 EPS enhancement were discussed. The results showed that Bsi20310 EPS effectively improved the FeCl3 coagulation performance on RX-3B dyeing wastewater. At pH 10 and Fe(Ⅲ) dosage of 55 mg/L, adding 200 mg/L Bsi20310 EPS yielded good decolorization of 93%, much higher than that (lower than 20%) obtained without EPS. The proper EPS addition timing according to Fe(III) addition can be controlled within 10-120 min. The negatively charged Bsi20310 EPS could neutralize the positive flocs of Fe(III)-RX-3B dye to form destabilized aggregations. Besides, Bsi20310 EPS can lead more ferric incorporated in coagulation by stimulating Fe(III) hydrolysis to form more larger Fe(III) polymers to form larger aggregations. The change of FT-IR spectra after coagulation indicated that-OH,-COOH and glycosidic bond might be the main functional groups. The PDA results showed that Bsi20310 EPS can bridge and sweep fine flocs to accelerate the setting rate of flocs. So Bsi20310 EPS can be applied as a safe and effective microbial coagulation enhancement.Adsorption behaviors and mechanisms of Bsi20310 EPS for lead ion from artificial freshwater and seawater had been studied. Effects of solution pH, EPS dosage and salinity on adsorption characteristics were evaluated. Different from most adsorbents, adsorption of lead onto Bsi20310 EPS showed better performance in seawater than in freshwater, which was about 119.80 mg/g in seawater versus 70.38 mg/g in freshwater, at pH 5.5,20℃and EPS dosage of 40 mg/L. The adsorption increased to the maximum at salinity of 35‰then reduced at higher salinities, indicating that it was favorable for Bsi20310 EPS adsorption for Pb(II) in seawater. Isotherms for the adsorption of lead from freshwater onto Bsi20310 EPS were analyzed and equilibrium data fitted well to Langmuir and Freundlich isotherm models. The kinetics for lead adsorption by Bsi20310 EPS can be well described by pseudo-second-order model for both adsorption processes in freshwater and seawater. The Fourier transform infrared spectroscopy (FT-IR) analysis indicated that the functional groups of Bsi20310 EPS such as-OH, C=O and C-O-C played important roles as adsorption sites. |
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