Interaction Of Iron Minerals With Pseudomonas Aeruginosa And Its Effect Mechanism On The Removal Of Cr(?)

With the rapid development of industry and the acceleration of industrial transfer,a large amount of chromate have been discharged discharged into the environment by various types of production industries,leading to Chromium far exceeded and severely endangering the ecological environment and human health.It is imminent to carry out the management of chromium pollutants environment.There are various of ferrous primary and secondary minerals,also including many microorganisms in soil and groundwater.Iron is also an important element in the growth of microorganisms because of its involvement in many important processes of cellular physiology.Iron is often combined with bacteria in many forms in the natural.Mineral and microorganism interact with each other and it have different impact on environmental geochemical and biogeochemical cycles of heavy metal ions.The dissertation mainly includes the following content:1.It is studied the effects of minerals on the reduction of Cr???by Pseudomonas aeruginosa,such as goethite.The reduction behavior characteristics of Cr???onto P.aeruginosa in aqueous solution containing goethite were investigated by presence of carbon source,the efffects of goethite dosage,bacterial inoculum size,pH value,ambient temperature and initial concentration of Cr???.The bacterial growth and distribution,synergistic effect between bacteria with minerals were performed by using X-ray diffraction?XRD?,Scanning electronic microscopy and Energy Dispersive Spectrometer)?SEM/EDS?,Fourier transform infrared spectroscopy?FTIR?and X-ray photoelectron spectroscopy?XPS?.The results showed that:?1?The addition 4 g·L^-1 of glucose provided the carbon source for the bacteria and served as an electron donor,which significantly enhanced the reduction ability of P.aeruginosa to Cr???,but the glucose utilization rate was decreased when the glucose was added to 6 g·L^-1;?2?In the range of 0-8 g·L^-1,the increase of dosage of goethite directly increased the adsorption sites of Cr???,which played a protective role on bacteria;?3?The increase in bacterial concentration accelerated Cr???reduction in the range of 0-6 g·L^-1?wet weight?;but due to the cluster effect and limited by the nutrients in the environment,there was no significantly improved;?4?The medium and high temperature and weak acid environment is favorable for the reduction of Cr???by P.aeruginosa,which is related to the activity of bacteria and their secreted enzymes,the dissolution of Fe???ions;?5?At low concentrations of Cr???,bacteria play a major role in the removal of Cr???,and goethite plays a supporting role;but goethite plays a major role at high concentrations.The characterization showed that goethite did not change the morphology and size of P.aeruginosa,even it formed goethite-P.aeruginosa complex.Cr???in solution can be directly reduced to Cr???by the enzymatic reaction of P.aeruginosa,and also reduced to Cr???by reduction of Fe?II?that generated by reduction of Fe???by P.aeruginosa.And the Cr???in solution may produce Cr?OH?₃ or FeCr_1-x?OH?₃ precipitates.2.In the simulated acid mine waste water of high-concentration Fe???,we studied the change of the structural characteristics of Pseudomonas aeruginosa and Cr???removal performance.The results showed that Fe???was loaded on the surface of Pseudomonas aeruginosa?Pa?in the form of lepidocrocite and tetragonal lepidolite and it is named Fe-Pa.The adsorption behavior characteristics of Cr???onto Fe-Pa in aqueous solution were investigated by evaluating optimum synthesis conditions,the efffects of biomass dosage,p H value,contact time,ambient temperature and initial concentration of Cr???.The physico-chemical properties of Fe-Pa were performed by using SEM/EDS,FTIR,XPS and Zeta potential.The best preparation condition of Fe-Pa was under Fe???concentration of 600mg·L^-1 with P.aeruginosa dosage of 0.5g·L^-1.The lower pH was more benefit for Cr???adsorption onto Fe-Pa.Cr???adsorption was a endothermic and spontaneous process and could reach equilibrium within 60 min.Pseudo-second-order kinetics model and Langmuir adsorption model fitted the experimental data well.Fe???was successfully loaded onto the surface of Pseudomonas aeruginosa,which provided a large number of activated sites for the adsorption of Cr???.Electrostatic interactions and surface complexation were inferred to be the main mechanisms of adsorption of Cr???on Fe-Pa.After 4 times of adsorption/regeneration test,the maximum removal efficiency of Cr???could maintain 72%,which indicates that Fe-Pa had an excellent reusability.The two ways to combination between Fe???and P.aeruginosa makes the different removal efficiency and mechanism of Cr???.The former is dominated by P.aeruginosa for the reduction of Cr???,and goethite plays a supporting role.Cr???is eventually removed as a precipitate of Cr???.But the latter is mainly the adsorption of iron hydroxide on the surface of P.aeruginosa.Bacteria play a supporting role with a small amount of Cr???reduction.It provides a theoretical basis for revealing that the interaction between ferrous minerals and microorganisms in epikarst environment can control the environmental geochemical behavior of Cr???.