Bioremediation Of Effluent From A Uranium Mill Tailings Repository In South China By Azolla-Anabaena

With the development of nuclear power,the demand for uranium is growing rapidly.However,uranium mining and processing have generated large amounts of uranium mill tailings.The uranium and other contaminants in the tailings have been released into the water in the repository due to weathering and eroding,and the effluent from the repository has become contaminated with the contaminants.They then transport to the surrounding environment through surface runoff and groundwater,causing serious environmental pollution and posing great threat to human health.Therefore,the remediation of radioactive wastewater from uranium mill tailings repository is an urgent problem to be solved at present.In recent years,plant-microbe symbiont for the remediation of wastewater has proved as an effective measure for the remediation of contaminants from wastewater by many domestic and foreign exports and scholars,and its removal rate for contanminants is higher than used plants or microbes alone.However,most of the research on them were conducted with the artificial wastewater rather than the actual wastewater.It is often the case that the actual wastewater contains combined contaminants,which may interfere with each other,and their removal will be more difficult.Therefore,the objective of this study was to investigate the remediation effect of the effluent from a uranium mill tailings repesity.And hydroponic experiments were conducted on the subcellulardistribution and chemical forms of uranium in the Azolla-Anabaena,to understand the detoxification mechanism of Azolla-Anabaena under uranium stress.The main results of this study are as follows:(1)The plant-microbe symbiont was kept in the effluent for 30 days,and it was found that U,Fe,Mn,Cu,Zn,Pb,Cd,TP,TN and SO42-reduced by 87.6%,99.1%,98.8%,88.2%,91%,78.3%,77.5%,93.4%,98.7% and 76.7%,respectively.Especially,the concentration of uranium reduced from 0.3166 mg·L-1 to0.0393 mg·L-1,which was below the limits of contaminants by the Department of Environmental Protection of China.The concentrations of Fe,Cu,Zn,Pb,TP and TN in the effluent reached the quality standard for drinking water.Therefore,the results showed that Azolla-Anabaena can be used for the bioremediation of the effluent from the uranium mill tailings repository.(2)Uranium was mainly distributed in the cell walls of Azolla-Anabaena,which indicated that the cell walls can effectively prevent uranium getting in the cells to reduce the toxicity of uranium to Azolla-Anabaena.As to the chemical forms of U,the ethanol-and water-extractable forms decreased with the increased of uranium concentration in hydroponic solution.Therefore,cell wall binding and chemical forms converting were the main tolerance mechanisms to uranium for Azolla-Anabaena.