Flocculating Activity And Adsorption Performance To The Metal Ions Of Exopolysaccharides Extracted From Arthrobacter Ps-5

Extracellular polysaccharide (EPS) of microbial origin is a complex macromolecules comprision of polysaccharide, protein, nucleic acids and lipids. EPS has many functions, such as flocculation ability, aggregating cells and preventing external harmful substances invading. In addition, EPS also plays an important role in biosorption to heavy metals. It contains large amounts of toxic heavy metals in industrial wastewater, sewage and pesticide residue, which is harmful to humans’health. The traditional methods for removing heavy metals include precipitation, ionic exchange and filtration. These methods have several disadvantages like low selectivity, incomplete removal and high cost. Biosorption of heavy metals by EPS has brought a new way to deal with the heavy metal pollution.The crude EPSs were prepared from the fermentation broth of Arthrobacter ps-5by centrifugation, ethanol precipitation, deproteinized and lyophilized with the culture medium supplemented with sucrose, glucose or starch, named EPSsuc, EPSglu and EPSsta respectively. Properties of EPSs were also evaluated to provide scientific evidences for the further research of exopolysaccharides. The main results were shown as following:1. The crude EPSs were prepared from Arthrobacter ps-5by ethanol precipitation, sevage method, and obtained purified EPSs by DEAE-52anion-exchange chromatography column, Sephadex G-100column, dialysis and freeze drying. Ultraviolet scan spectrum analysis indicated that the purified EPSs were absence of proteins and nucleic with no absorption at260nm or280nm. The EPSs were all composed of glucose and galactose detected by thin layer chromatography (TLC).2. The flocculation ability and influence factors of the EPSs in kaolin and activated carbon suspension were investigated:the maximum flocculation rate in kaolin was91.45%with Ca2+added; and the maximum flocculation rate in activated carbon was81.07%with K+added.3. The biosorption of Pb2+, Cu2+and Cr6+by EPS were investigated. The influences of EPS dosage, pH and equilibrium time on adsorption property were studied. The results shown that the proper EPS dosages were1.0mg/mL,1.0mg/mL and0.8mg/mL respectively. The optimum pH for the adsorption of Pb2+, Cu2+and Cr6+were5.5,5.0and6.0. The adsorption equilibrium time of Pb2+, Cu2+and Cr6+by the EPS were2h. The highest adsorption capabilities of Pb2+, Cu2+and Cr6+by EPS were225.40mg/g,183.67mg/g and86.97mg/g separately. The adsorption ability of Pb2+, Cu+and Cr+decreased significantly with the addition of Ca2+and K+. With the content of Ca2+and K+increasing, the degree of adsorption reduction was greater, and the effect of inhibition was more obvious. So the metal ions such as Ca2+and K+were competitive with the target metal ions.4. The structural characterization of the three different EPSs indicated:the ratios of acidic polysaccharide/neutral polysaccharide in the EPSs were different. The ratio was higher, the biosorption capacity was stronger.5. IR analysis demonstrated that the groups of O-H, C=O,-COOH and C-O-C of polysaeeharide were the main functional groups for binding metal ions.