The Isolation And Identification Of Urease-producing Bacteri And Its Application On The Remediation Of Cd Contamination

With the rapidly development of mineral mining and electroplating industry,the cadmium?Cd?pollution problems are poseing a serious threaten to China's soil and water.Because of its long-term latent and highly carcinogenic,the Cd would be enriched in visceral organ of animals and humans through the food chain,which would take irreversible toll on the bones,reproductive and urinary system.Therefore,there is a urgent need to find an efficient,low-cost method against the Cd pollution.Nowdays,microbial induced carbonate mineralization?MICP?technology is a hotspot in the field of harness of soil and water polluted by Cd.The urease secreted by Urease-producing germ could promote the hydrolysis of urea specificity,yeild the CO₃^2-ions and NH₄⁺ions,while improving the environmental pH.In the meantime,the Cd²⁺ions in the soil and water would react with CO₃^2-ions,yeild the carbonate precipitation then set down.The shortage of recent research of this field are made up by our research contents and contributions,which are as follows:?1?In this study,a highly productive Urease-producing strain was isolated from the red brown soil of Hubei Province,named by UR-2.The growth period of UR-2was 72 h,more than 95%urea was hydrolysied after training period.The tolerance to Cd concentration of this strain was 30 mg/L,but it seems to be more suitable for alkaline conditions.?2?It was affirmed that in the liquid condition,UR-2 has the ability of inducing Cd²⁺ions to mineralizate,this ability was influenced by different conditions of envierenment.The results of XRD and EDS showed that the mineralization products were CdCO₃.Based on the results of SEM and IR,it was found that the Cd²⁺ions were adsorbed on the cell wall of the Urease-producing bacteria,then the Cd²⁺ions as effective crystallization sites were bindng with CO₃^2-ions,which formed a coating on the cell surface.The pH and temperature conditions had a significant impact on this curing ability of Cd²⁺ions.Under different pH conditions,it was shown tha the particle size,morphology and composition of the mineralized products were severe changed,whereas there was little effect of temperature conditions.?3?UR-2 was also showed up to has the carbonate mineralization ability of Cd²⁺ions in the soil.Under the action of UR-2,in the weakly acidic soil,the curing rate of Cd²⁺ions reached 39.9%,meanwill,it attained 67.7%of the alkaline soil.The EDS and XRD analysis showed that the cured products of acidic soil were CaCO₃ and CdCO₃.Ca²⁺and Cd²⁺ions were found to adsorbe on the bacterial cell wall of bacteria growing on SiO₂,then they crystallized on the adsorption site,based on the SEM and IR results.It is shown that CaCO₃ and CdCO₃ form a co-crystal in a lattice doping manner from EDS-mapping results.