Screening Of Lead And Cadmium-resistant Bacterium And Research Of Their Adsorption

With the rapid development of industries,a large number of heavy metals were discharged into the environment,which caused serious pollution.Traditional treatment methods suffer from high investment,operating costs and secondary pollution.Because of high efficiency,low energy,environmentally friendly,biological treatment of heavy metal pollution has been focused on.Using dilution plate method,two strains resisted to high concentration of Pb2+、Cd2+ were isolated from heavy metal contaminated soil in Ganzhou,Jiangxi province. Enterobacter sp.S:the tolerant concentration of Pb2+ and Cd2+ was 1300 mg/L and1800 mg/L,respeetively.The strains R : the tolerant concentration of Pb2+ and Cd2+ was 1100 mg/L and1200 mg/L,respeetively.The optimization results to growth of stains S and R show that the optimal temperature is 40 ℃, the optimal range of p H value is 7.0-7.5, the optimal concentration of Na Cl is 0.5% and 1% 。 Traditional biochemical charasteristics and modern molecular biological methods-16 S r DNA sequencing showed that one strains was in genes of Enterobacter sp.,named Enterobacter sp.S.The other is identifying now using 16 S r DNA sequencing.,named stains R.The non-living S and R used as bioabsorbent possessed good adsorption ability for Pb2+ or Cd2+. Adsorption performance of the bioabsorbent was affeced by the fungus age. Promoting the solution p H value increased the adsorption to Pb2+ and Cd2+,but high p H value is not conducive to adsorption. Adding the dosage enhanced the removal rate but reduced the adsorption capacity. The adsorption capacity were inereased initially,and then dropped with the increase of temperature. When adding the concentration the adsorption was increased,but removal rate decreased.The influence of time on adsorption indicated the adsorption of two strains on Pb2+ and Cd2+ is a rapid process,and 60% of adsorption capacity could be accomplished.The adsorption process of S and R was studied by isotherm.Langmuir and Freundlich model deseribed the adsorption of strains S on Pb2+ perfectly. The correlation coefficient of Langmuir and Freundlich isotherm equations have reached 0.99 of strains S on Cd2+. Langmuir and Freundlich model could not better simulate the experimental results of strains R on Pb2+. Langmuir model deseribed the adsorption of R on Pb2+ perfectly.Results of SEM showed that the structure of strains surface was damaged. Results of EDX showed that the strains had adsorbed Pb2+ and Cd2+. Results of FTIR showed that the intensity of –OH、–NH2、–COOH、–PO3 decreased after adsorption. Results of XRD showed that some new substance was formed after adsorption. After the chemical treatment of –NH2、–OH、–COOH、–PO3,the absorption of Pb2+ and Cd2+ reduced in different degrees,which indicated that the three functional groups played a important role in the adsorption proeess.Desorption results showed that EDTA was the best desorption chemical,and desorption rate is more than 90%. Chemical modification results showed that the adsorption capacity on Pb2+ or Cd2+ was improved apperantly after modified by Na OH.