Remediation Of Organic Contaminated Sites By Electrokinetic-enhanced Groundwater Circulation Well

With the rapid development of economy and the increase of industrial and agricultural production and the intensity of human activities,soil and groundwater pollution problem has become increasingly prominent.The organic pollution of soil and groundwater has the characteristics of persistence,concealment,complexity and difficulty in management,which has been paid much attention by researchers and governments at home and abroad.This paper selects three kinds of different volatile organic pollutants in toluene,methyl tert-butyl ether(MTBE)and decabromodiphenyl(BDE-209)as the representative of the risk quotient of contaminated sites,and aiming at the lack of standard of contaminated sites in our country,calculate the criteria maximum concentration(CMC)and criteria continuous concentration(CCC)of three organic contaminants in surface water and soil,which using CMC as the reference value of the repair target.According to the groundwater circulation wells(GCW)of volatile and semi volatile organic compounds treatment effect is good,and there are characteristics of the repaired tailing phenomenon,this paper combined the electrokinetic technology(EK)with GCW,studied the effect of EK-GCW on the repair of contaminated site and the improve of the tailing phenomenon,and discussed the effects of target pollutant remediation effect of strengthening natural attenuation.The main conclusions are as follows:(1)Risk assessment and criteria value calculation of target pollutantsThe paper uses the risk quotient entropy to evaluate the surface water of 8 regions in China and the soil in the 12 regions.The CMC of toluene,MTBE and BDE-209 in surface water were 4.70 mg/L,97.50 mg/L and 4.735×10-7 mg/L respectively,and CCC were 0.14 mg/L,1.70 mg/L and 9.47×10-10 mg/L.The CMC in soil were 100 mg/kg,87.80 mg/kg and 1.00 mg/kg,and CCC were 2.00×10-3 mg/kg,0.18 mg/kg and 2.00×10-3 mg/kg.(2)Remediation of organic contaminated sites by GCWThe adsorption of toluene,MTBE and BDE-209 in sandy soils were in line with the Langmiur isotherm,Linear isotherm and Freundlich isotherm,and the adsorption coefficients were 4.45×10-2 m3/kg,3.06×10-3 m3/kg and 1.71×10-2 m3/kg respectively;the adsorption equilibrium time was 24 h,24 h and 48 h.Building GCW simulated device was to repair target pollutants on sandy soil and aquifer,in which the best operating conditions as follows: aeration rate 400 L/h,extraction rate of 72 L/h,the average removal of the best running time of 15 h.The average removal rate of toluene and MTBE in aquifer respectively were 92.3% and 77.3%;while in soil the maximum removal rate were respectively 95.4% and 93.8%.But the single GCW technology had no obvious effect on the remediation of BDE-209.(3)Remediation of organic contaminated sites by EK-GCWIn aquifer,after 15 h EK-GCW operation that the average removal rate of MTBE was 93.1%,and the highest removal rate was 97.2%,which was 12.1% and 11.7% higher than the single aeration,respectively.The tailing concentration of MTBE decreased from 113.50 mg/L to 34.5 mg/L,it less than CMC.After 40 h of EK-GCW operation,the removal rate of BDE-209 was 74.3%,with the highest removal rate of 94.2%(D2).Most of the BDE-209 was mineralized by hydroxyl radicals.After 40 h of operation,the removal rate of BDE-209 at the C1,C4 and C6 sampling sites was 89.4%,80.4% and 79.6%,respectively.The removal efficiency of combined pollution was faster than single pollution by EK-GCW under same working time,but the final effect was consistent.(4)Effects of enhanced natural attenuation on restorationThe combination of EK and GCW can effectively remove the BDE-209 in the soil and aquifer,and the toluene and MTBE in the aquifer reach the target value,but the tailing concentration is higher.Therefore,the effect of microorganisms on the removal of toluene,MTBE and BDE-209 in the aquifer was studied by GCW intermittent aeration.After 7 d of intermittent aeration,the concentration of toluene,MTBE and BDE-209 were decreased from 4.02 mg/L,32.72 mg/L and 6.27 mg/L to 1.1 mg/L,10.45 mg/L and 4.24 mg/L,respectively.The average concentration of toluene and MTBE in aquifer was much lower than CMC.However,the average concentration of BDE-209 was higher than that of CMC,thus could be considered to achieve the goal of remediation effect by inoculating aerobic microbial strains.The experimental results show that the combination of EK and GCW can effectively improve the removal efficiency of MTBE in sandy soil and groundwater,and has a good repair effect on BDE-209,which can effectively extend the repair range of GCW.Enhancement of natural attenuation by intermittent aeration can effectively reduce the tailing concentration of target pollutants.Therefore,for toluene and other volatile organic compounds,the combination of GCW continuous aeration with intermittent aeration combination can achieve restoration goals.For MTBE and other hydrophilic volatile organic,GCW was used for aeration in the severe pollution stage,EK-GCW was used to repair in the medium term,and intermittent aeration was used to remove effectively target pollutants in the later stage of repair.For BDE-209 and other persistent organic pollutants,EK-GCW can be used to enhance the natural attenuation with the combination of aerobic microbial strains to achieve the target value.