| Cadmium poses a serious threat to environmental ecological security due to its strong biological toxicity and inability to be degraded.Cadmium pollution and its treatment have attracted more and more attention,among which biological method has broad application prospect because of its advantages of high efficiency,low energy consumption and environmental protection.This paper use of microbial cultures,element analysis and molecular biology techniques for the resistance to cadmium containing cadmium soil bacteria screening,the study of cadmium adsorption characteristics and influencing factors,analyzing the characteristic of the cadmium bacteria resistant gene,and reveal the biological mechanisms of cadmium adsorption,so as to the development of microbial adsorbent and heavy metal Cd pollution of wastewater to provide theoretical basis and technical support.The main research conclusions are as follows:(1)Through screening and identification of Cadmium-resistant bacteria in soils containing cadmium,three strains with strong cadmium absorption were obtained:Bacillus subtilis,Enterobacter cloacae and Hafnia alvei.(2)The optimal adsorption conditions for three strains of Cd2+were determined as follows:? Bacillus subtilis:pH6.0,temperature 34?,initial concentration of Cd2+10mg/L,bacteria dosage 25g/L,and the maximum adsorption rate was 65.8 ±7.25%;? Enterobacter cloacae:pH7.0,temperature 34?,initial concentration of Cd2+10mg/L,bacteria dosage 20g/L,the maximum adsorption rate was 88.79 ± 1.59%;? Hafnia honeycomb:pH6.0,temperature 34?,initial concentration of Cd2+20mg/L,bacteria dosage 25g/L,the maximum adsorption rate was 92.13±0.92%.(3)The change of Cd2+adsorption efficiency of bacteria under different concentrations of carbon source,nitrogen source,phosphorus source and COD was discussed.The results showed that:with the increase of pollutant concentration,the adsorption rate of bacteria to Cd2+decreased significantly.The change of carbon source and phosphorus source had the greatest influence on Hafnia honeycomb,and the adsorption rate of Cd decreased by 33.17%and 19.99%,respectively.The change of ammonia nitrogen and total nitrogen had the greatest effect on Enterobacter cloacae,and the adsorption rate of Cd decreased by 38.53%and 35.39%,respectively.The change of COD had the greatest influence on Bacillus subtilis,and the adsorption rate of Cd decreased by 47.4%.(4)The results of gene sequencing indicated that the mechanism of cadmium adsorption by Hafnia honeycomb might be intracellular accumulation:Cd2+in the environment enters the cell through the ion transport system of Mg2+and Zn2+on the cell membrane,forms metal chelates with Fe-S cluster-binding proteins,Lac Family and other proteins,or with sulfur ions and phosphate ions in metabolites,and precipitates,generating phosphate precipitates. |
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