Characterization And Mechanism Of Cd²⁺ Adsorption By Cadmium-tolerant Bacillus Sp.strain PFYN01

Heavy metal cadmium has strong biological toxicity,it is not easy to be degraded.Due to high migration,it is easy to enrich in the animal and plant through the food chain,which seriously endangers the environmental and ecological safety.In this thesis,a cadmium-tolerance Bacillus sp.PFYN01 was isolated and domesticated from the slag-contaminated silt in Panzhihua mining area.The strain can be used as a microbial adsorbent for heavy metal Cd²⁺,has the advantages of rapid propagation speed,short processing time and low cost,and is friendly to environmental protection.The cadmium-resistant growth characteristics,cadmium adsorption characteristics and adsorption mechanism of Bacillus sp.PFYN01 strain were studied systematically.The adsorption characteristics,adsorption conditions optimization and adsorption behavior of this strain on main pollutant Cd²⁺in wastewater were also studied.these researches provide theoretical and experimental support for the application of microbial adsorbents in industrial wastewater treatment.The mainly conclusions present as follows:?1?Carrying out strain domestication by increasing the concentration of Cd²⁺gradually,and a strain PFYN01 capable of tolerating high concentration of Cd²⁺was selected,which belongs to the genus Bacillus and is a Gram-positive bacterium.Optimization of growth conditions,plate growth under different Cd²⁺concentrations and tolerance to other heavy metals.The results showed that the strain had a pH of 5-7and a liquid volume of 90 mL.The growth condition was good in 50 mg/L Cd²⁺liquid medium.When the concentration of Cd²⁺was over 100 mg/L in liquid medium,the growth of the strain was gradually inhibited to some extent.However,it still can thrive in a solid medium with a concentration up to 3900 mg/L Cd²⁺.indicating that the strain is Cd²⁺.All the results indicate that the strain is highly resistant to Cd²⁺.The tolerance to other heavy metals is Cd>V>Zn>Pb>Cu.Several heavy metal tolerance experiments suggest that this strain has great potential for heavy metal pollution remediation.?2?The adsorption experiment of Cd²⁺was carried out with strain as adsorbent.The effects of pH,Cd²⁺concentrations,adsorption equilibrium time and temperature on the adsorption of Cd²⁺were investigated,and the results were further fitted by kinetic equation and isothermal adsorption.The results show that the optimum adsorption Cd²⁺by strain PFYN01 are 75 mg/L Cd²⁺,pH 5,and 1 g/L added bacteria amount and the adsorption equilibrium could be achieved within 1 h.The adsorption process accord with the second-order kinetic model and Freundlich adsorption isotherm.The adsorption conditions were optimized to obtain a saturated adsorption capacity of 19.02 mg/g,indicating that the adsorption process is based on chemical adsorption.It is expected to achieve treatment effects and economic requirements in actual industrial wastewater.?3?After cadmium induced acclimation,the cadmium adsorbed by PFYN01lyophilized cells was concentrated in the cell wall,and the lyophilized cells were adsorbed by cadmium.The adsorption capacity of cadmium was obviously enhanced,indicating that the adsorption of cadmium was mainly cell wall adsorption;The ability of cells and cell walls to adsorb cadmium was greatly improved,increasing by 76%and 54%,respectively.The adsorption capacity of cells and cell wall after sodium hydroxide treatment decreased,indicating that cell wall damage will reduce the adsorption capacity of cadmium.?4?The physicochemical properties were characterized and analyzed by SEM-EDS,FTIR,XRD,intracellular accumulation of different components and different distribution experiments and desorption experiments.The results indicate that the cell structure is complete after treating by 20 mg/L Cd²⁺,but there are many wrinkles on the surface of the cell,and no cell breakage.Some cells have cell hulls of different sizes,and denaturation reactions may occur in the cells.The appearance of the cell empty hulls indicates that a certain concentration of Cd²⁺will cause damage to the cells.When grown at a concentration of 300 mg/L Cd²⁺,the surface wrinkles of PFYN01 cells are more obvious,some cells were perforated.Small particles of the intracellular material are deposited on the cell surface,indicating that the intracellular material is completely lost and forms a complex with Cd²⁺.It is speculated that Cd²⁺concentration on the surface is high,and there is a large osmotic pressure gap inside and outside the cell.More Cd²⁺is transported into the cell,causing the cell contents to quickly overflow from the hole.The strain PFYN01 detects the participating functional groups by FTIR,such as-OH,N-H,-CH,C=O,etc.,wherein-OH and C=O are preferential adsorption points.XRD experiments show that Cd²⁺-adsorbed bacteria has obvious Cd²⁺characteristic peaks at 13°and 39°,respectively.?5?The basic parameters and heavy metal composition analysis of the sewage outlets of the four enterprises were carried out,and it was found that the cadmium content of the four sewage outlets exceeded the national industrial second-class discharge water quality standards.Adding strains for adsorption experiments,the removal rate of Cd²⁺in industrial wastewater by strain PFYN01 reached 91.46%,and the Cd²⁺content in the water after adsorption reached the national industrial second-class discharge water quality standard,indicating that the strain has good industrial heavy metal pollution control prospects.