Column Experiments On Perchlorate Natural Attenuation Enhanced By Different Electron Donors

Perchlorate（ClO₄^-）,which is a toxic inorganic complex anion with low molecular weight,is a widespread contaminant in environment.It becomes the extensive concerning environmental contamination problem because it is known to impact thyroid function by replacing iodine intake due to its similar molecular size with iodine.Column experiments were conducted to study on stimulating natural attenuation of the target pollutant ClO₄^-.What included in this study are investigations of effectiveness and durability of ClO₄^-natural attenuation using granular iron,sulfur and pine bark as electron donors respectively.Effects of different environmental factors on ClO₄^-reduction were also discussed.All of that give theoretical basis and data support for practical application of in-situ remediation of ClO₄^-in groundwater.Main contents and results of this study are as follows:⑴ ClO₄^-natural attenuation mainly depends on microbial degradation in the aquifer,but the process was slow and the reduction amount was limited.Lacking of electron donors resulted in long-term removal efficiency less than 10%.⑵Granular iron,sulfur and pine bark can act as electron donors during natural attenuation of Cl O₄^-.Microbial adaptability was proved in every stimulated process.Based on the chlorine balance calculation,ClO₄^-was reduced to Cl-almost completely without generation of other chlorinated products.⑶ Long-term removal efficiency of ClO₄^-was less than 70% due to the iron passivation in the granular iron stimulation system.Sulfur stimulation system`s removal efficiency was less than 60% when lacking of microelement,while the removal efficiency stayed at 100% after groundwater pumping.The removal efficiency almost stayed at 100% in pine bark stimulation system.Pine bark showed significant advantages in effectiveness and adaptability over other electron donors,proving it a desirable electron donor.⑷The existence of nitrate（NO₃^-）had an inhibitory effect on ClO₄^-reduction due to competition of electron donor between NO₃^-and ClO₄^-.When electron donor was adequate,electron donor competition wasn’t evident and NO₃^-and ClO₄^-can be reduced rapidly.When electron donor went insufficient,reduction of NO₃^-was prior to ClO₄^-.Only when NO₃^-concentration was less than 10 mg/L could ClO₄^-initiate an apparently reduction.⑸Although some of the anions in groundwater had an inhibitory effect on ClO₄^-reduction because of competition of electron donor,ground water was a necessary condition to ClO₄^-natural attenuation since trace elements in groundwater exerted a stimulating effect during the process.