Flocculation And Adsorption Properties Of An Exopolysaccharide From The Deep-sea Psychrophilic Bacterium Pseudoalteromonas Sp. SM9913

Pseudoaltermonas sp.SM9913,a psychrophilic bacterium isolated from 1855 m deep-sea sediment can secrets a lot of sticky exopolysaccharide.The flocculation and adsorption ability and mechanism was investigated in this paper.The flocculation performance in kaolin suspension has been studied first.The effects of EPS dosage,pH,co-ions,salinity and temperature on the flocculation of EPS SM9913 were investigated.The flocculation Mechanism of EPS SM9913 had been studied by determining zeta potentials and flocs sizes during flocculation process. By deacetylating EPS SM9913 and measuring the flocculating activity of the deacetylated EPS,the function of the acetyl groups was studied.Additionally,the best storage method of this EPS was also determined.The results show that EPS SM9913 has a peak flocculating activity of 49.3 in 1 g/L kaolin suspension with 4.55 mmol/L CaCl₂ and the optimum pH range of 5～8.It appears that the flocculating activity of EPS SM9913 is stimulated by Ca²⁺and Fe²⁺and is highest in NO₃^- solution among various anions solution.This study also found that EPS SM9913 shows a better flocculation performance than Al₂(SO₄)₃ at salinity of 5～100‰or temperatures of 5～15℃.In addition,EPS SM9913 is effective to flocculate several other suspended solids.The measured Zeta potentials,the size of flocs formed during the flocculation process and the surface profile of flocs revealed by scan electron micrograph suggest that bridging is the main flocculation mechanism of the studied EPS SM9913. Deacetylation of EPS SM9913 results in a significant decrease in its flocculating activity indicating that the large number of acetyl groups in EPS SM9913 plays an important role in its flocculation performance.EPS SM9913 could be stored without desiccation in 4℃,as it has no decrease in flocculating activity during study period.Biosorption of Pb²⁺and Cu²⁺by EPS SM9913 was also investigated.The influences of EPS dosage,pH,equilibrium time and coexisted-ions on adsorption property and the adsorption isotherm of this EPS were studied.The results show that the equilibrium adsorption capacity(Q_e)decreases with the increase of EPS dosage. The optimum pH for the adsorption of Pb²⁺is during 4.5～5.5,and for the adsorption of Cu²⁺is during 4.5～6.The Cu²⁺adsorption equilibrium is attained within 90min, while the Pb²⁺adsorption equilibrium time is 180min.Q_e of Pb²⁺decreases with the addition of co-ions as Ca²⁺,Mg²⁺,Na⁺ and K⁺.Addition of Ca²⁺,Mg²⁺also decreases the Q_e of Cu²⁺,but low dosage of Na⁺ and the tested dosage of K⁺ in study increases the Q_e of Cu²⁺.Both Freundlich and Dubinin-Radushkevich isotherm equations could well describe the thermodynamics process of Pb²⁺and Cu²⁺by the EPS.The maximum adsorption capacity determined by Dubinin-Radushkevich isotherm equation for Pb²⁺and Cu²⁺are 243.3 mg/g(10℃)and 36.7 mg/g(40℃).IR analysis demonstrates that the group of C—O—C,acetyl and hydroxyl of polysaccharide are the main functional groups for binding metal ions.