The Behavior And Mechanism Of Plant-microbial Symbiotic Purification System For Repairing Low-concentration Uranium Wastewater

By using the hydroponic experiments,advantageous plants capable of accumulating uranium from low-concentration uranium-containing wastewater were screened out in this dissertation.Then the plant-microbe symbiotic purification system was constructed from these advantageous plants.After that,the effect of this system on remediating low-concentration uranium-containing wastewater and the detailed mechanism were discussed.The remediation effect of this system was compared with that of microbial system.The main content and conclusions were as follows:1.On the base of the preliminary field investigation,the advantageous plants capable of efficiently remediating low-concentration uranium-containing wastewater were screened out by using the uranium resistance experiments and the hydroponic experiments.The results showed that Typha orientails presl,Syngonium podophyllum,Spathiphyllum kochii,Cyperus iria L and Juncellus serotinus were advantageous plants due to the high uranium tolerance property and the strong remediation capability.2.Spathiphyllum,fernleaf hedge bamboo,and C.iria were selected to construct the plant-microbe symbiotic purification system,with a superior microbe,Aspergillus niger.The capabilities of uranium-removal of these three plants-Aspergillus niger symbiotic purification system.The effects of the initial pH value and the additives,such as carbon source and nitrogen source,were also investigated.The results showed that the optimal pH value was 7.At pH 7,Spathiphyllum-Aspergillus niger symbiotic purification system could remove more uranium than the other purification systems.In 12 days,the removal efficiency could attain 98.1%.The optimal additive should comprise 4 g of glucose,as carbon source,and 0.4 g of ammonium sulfate,as nitrogen source.Meanwhile,it was demonstrated that microbe,with biofilm formation,could remediate low-concentration uranium-containing wastewater combined with plants.3.The endophyte Pseudomonas sp.XNN8 was separated from Typha orientails presl which could secrete indole-3-acetic acid,1-aminocyclopropane-1-carboxylate deaminase and siderophores.Pseudomonas sp.XNN8 exhibited strong resistance to uranium,thus was colonized in Syngonium podophyllum.Then the as-constructed Syngonium podophyllum-Pseudomonas sp.XNN8 symbiotic purification system?SPPSPS?was used to remove low-concentration uranium in the hydroponic experiments.The mechanism of wastewater remediation was investigated by Fourier transform infrared spectroscopy?FT-IR?and extended X-ray absorption fine structure spectroscopy?EXAFS?.The optimal pH value turned out to be 6.At pH 6,the SPPSPS could effectively remove low-concentration uranium in the wastewater.The concentration of the uranium-containing water could decrease to 0.05 mg/L in 24 days,when the initial concentration was between 0.5 and 5.0 mg/L.It was indicated that Pseudomonas sp.XNN8 may promote adsorption of uranium through secreting such metabolitesasindole-3-aceticacidand1-aminocyclopropane-1-carboxylate deaminase and siderophore.Winding and immersion-type invasion were two efficient ways to colonize the entophyte into plants.Pseudomonas sp.and S.podophyllum could produce unsaturated functional groups such as NH₂,-OH,and–CHO,which could react with more hydrolyzed uranium ions through coordination and complexation,and thus promote the adsorption of uranium.The uranium in the roots of the S.podophyllum in the SPPSPS was in the form of uranyl phosphate?47.4%?and uranyl acetate?52.6%?.4.In the preliminary stage of the experiment,we selected Deinococcus radiodurans and E.coli JM109 as raw materials to prepare bio-adsorbent for uranium.The adsorptions of both bacteria for uranium were studied.The influence factors as pH value,temperature,adsorption time,initial uranium concentration and bacteria concentration were all investigated.Meanwhile the thermodynamics and kinetics were also analysized.Compared with the results of the plant-microbe symbiotic purification system,Deinococcus radiodurans and E.coli JM109 were both effective in uranium adsorption from wastewater.After comparing remediation efficiency,stability of microbial colonization and controlled conditions of repair technology of different remediation methods,we concluded that the as-constructed SPPSPS would be the best candidate for remediation of low-concentration uranium-containing wastewater.