Research On Immobilizing Bacteria Strains By Magnetic Graphene Oxide And Its Adsorption Of Cd²⁺

In recent years,water pollution caused by heavy metals is very serious.Immobilized microorganism technology is an effective way to solve this problem.Owing to its strong treatment effect,wide applicability and multiple recycling,Immobilized microorganism technology has become the current research hotspot.In this study,the strains with good tolerance to cadmium were separated from polluted environment,constructed into composite flora and immobilized on magnetic zinc oxide graphene material.Meanwhile,MGO immobilized microorganism beads were successfully prepared and the treatment effect of the immobilized beads on Cd2+was studied.The main research results are as follows:?1?Five strains of bacteria with good tolerance to cadmium were screened from polluted environment,and their physiological and biochemical characteristics and growth characteristics were studied.Three strains of bacteria?P2,X,N?were selected to construct the composite flora.The optimal inoculation ratio of the composite flora was determined to be 2:3:1 through experimental optimization.Under this condition,the adsorption and removal rate of cadmium by the composite flora could reach 56.6%.In addition,through molecular biological identification,P2,X and N strains of bacteria have high similarity with Pseudomonas aeruginosa.?2?Graphite was used as material to prepare magnetic graphene oxide?MGO?material by improved Hummers method and chemical coprecipitation method.The magnetic graphene oxide?MGO?material was characterized by infrared spectrometer?FTIR?,scanning electron microscope?SEM?and vibrating sample magnetometer?VSM?.The results show that Mg O has rich functional groups and dense pore structure,and its saturation magnetic field strength reaches 42.64 emu/g,which can easily realize magnetic separation.?3?Taking the appearance characteristics,particle size,strength and mass transfer property of the immobilized beads as indexes,the single factor experiment and orthogonal experiment were used to determine the optimal preparation conditions of the immobilized beads:sodium alginate mass fraction?4%?,MGO mass fraction?0.8%?,and bacteria inclusion amount?5 m L?.Under these conditions,the adsorption and removal rate of cadmium by the prepared beads was 83.09%.?4?The treatment effects of solution pH,initial concentration,dosage,time and ambient temperature on Cd²⁺by immobilized beads were tested.The results showed that the optimal reaction conditions for immobilized beads were pH=5,initial concentration40 mg/L,dosage 10 g/L,adsorption time 12 h,and ambient temperature 30?.?5?Adsorption kinetics and thermodynamic models were used to fit the adsorption process of Cd2+onto immobilized beads.The results showed that at different initial concentrations,the quasi-second-order kinetic equation has higher fitting degree than the quasi-first-order kinetic equation,and the adsorption reaction is mainly chemical adsorption.At different temperatures,Langmuir model and Freundlich model can well describe the adsorption process of immobilized beads,but Langmuir model has a higher fitting degree.The adsorption process is dominated by monolayer adsorption with the maximum adsorption capacity of 113.298 mg/L.?6?The adsorption and desorption results showed that the immobilized beads have good performance.After 5 times of adsorption and desorption experiments,the immobilized beads still have high adsorption effect and can be recycled for many times.