| 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.Three strains resisted to high concentration of Cr6+, Pb2+, Mn2+, Cd2+, Zn2+, Cu2+, Ni2+, Co2+, Ag+, Hg2+ were isolated from heavy metal contaminated soil in a factory in Hunan province, China. Traditional biochemical charasteristics and modern molecular biological methods-16S rDNA sequencing showed that one strain was in genes of Pannonibacter phragmitetus, named Pannonibacter phragmitetus T1. Colonial morphology was round, neat edge, dry and thick surface, intermediate uplift, milky white, non-proliferation. The second strain was in genes of Enterobacter sp.,named Enterobacter sp.T2. Colonial morphology was round, neat edge, moist and thick surface, khaki-colored, non-proliferation. And the third strain was in genes of Microbacterium sp., named Microbacterium sp.T3. Colonial morphology was round, neat edge, smooth, thick and moist surface, bright yellow, non-proliferation.The tolerant concentration of Pb2+ and Mn2+ was 2000 mg L-1 and 1500 mg L-1, respectively. Taking the conolial morphology of T1 in medium with half the MIC of heavy metals as an example, the shape and color changed obviously in Pb2+, Cr6+ and Mn2+ containing medium but slight in others.The non-living T1, T2 and T3 used as bioabsorbent possessed good absorbability for Pb2+. Adsorption performance of the bioabsorbent was affected by the regulation of metabolic activity and incubation time of bacteria. Promoting the solution pH value increased the absorbance and removal rate of Pb2+. Adding the dosage enhanced the removal rate but reduced the absorbance. The absorbance and removal rate were increased initially, and then dropped with the increase of temperature. When adding the concentration the absorbance was increased but removal rate decreased. Appropriately enhancing the rotational speed increased the absorbance but exceeding over a limit decreased the absorbance. The adsorption process could be divided into three steps:fast adsorption, slow adsorption, equilibrium adsorption; and 90% of absorbance could be accomplished in the fast adsorption stage.The adsorption process of T1, T2 and T3 was studied by kinetic and isotherm. It is found that Pseudo-second order equation, with more than 0.99 of the correlation coefficiency, dipicted the sorption process of the three absorbents very well. Langmuir model described the adsorption of T1 pefectly, The correlation coefficient of Langmuir and Freundlich isotherm equations have reached 0.99 of T2, Freundlich model could better simulate the experimental results better of T3.Results of SEM, EDX and FTIR showed that Pb2+ ion was adsorbed effectively by the bioabsorbent. According to the FTIR, the adsorption of OH-NH-, O=C-O- and -PO43- was shifted after absorbing Pb2+, which illustrated that these functional groups participated into the adsorption. After the chemical treatment of functional groups of bacteria, the adsorption of Pb2+ was reduced in different degrees, which indicated that the three functional groups played a role in the adsorption process.Desorption and chemical modification results showed that EDTA was the best desorption chemical while Pb2+ adsorbability of the biosorbent was improved apperantly after the modification with sodium hydroxide. |
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