Remediation Of NAPL Contaminated Aquifer With Surfactant-enhanced Groundwater Circulation Well

In recent years, groundwater organic pollution incidents are frequently occurredin china especially duing to the waste leakage, discharge and explosion, and havebecome the urgent problems in the environmental domain. Groundwater circulationwell is a effective mean to removal volatile organic compounds and has been proveneffective in the processing of field remediation application. However, the study ofGCW has just began in china, and ROI (radius of influence) representation andrelated influencing factors, concentration attenuation of organic compounds as wellas the zone of influencing are all needed to study systematically. In the light of thelow aqueous solubility of NAPL (Non Aqueous Phase Liquids), surfactant-enhancedaquifer remediation is considered to be the most effective in situ remediationtechnology. In the past research, most studies focused on the mechanism study, whilethe dynamic flushing process needs further research.According to the previous studies, benzene, nitrobenzene and naphthalene werechosen as the typical NAPLs, and the remediation effect of contaminated aquiferwith surfactant enhanced groundwater circulation well was carried out. A series ofsimulations experiments were conducted to investgate: radius of influence of GCWand the influencing factors, such as groundwater initial level, aeration rate,groundwater velocity and structure of GCW; the effect of GCW, including thesorption of organic compounds on different experimental medium, concentrationattenuation of contaminants in the process of CGW and the zone of influence ofGCW; the effect of SEAR, including: the surfactant selection, the critical flushingconcentration as well as the influencing factors; surfactant-enhanced GCW, including the hydraulic control of surfactant by GCW, the surfactant sulibilozaiton,concentration attenuation of organic compounds and the zone of influence.A two-dimensional sand tank was used to identified the ZOI of GCW, the effectof influencing factors, such as groundwater initial level, aeration rate, groundwatervelocity and structure of GCW were all studied, the results demonstrate that:(1)maximum horizontal distance of the zone that water level change can be defined asthe ROI of GCW;(2) the higher of the initial groundwater level, the smaller of thecritical aeration rate and the stronger of the ciucuration of groundwater.(3) aerationrate was positive to∑△h, but has litter influence on ROI.(4) A slight increment of∑△h was observed when the groundwater flow velocity increased from0.1to1.0m/d, but the ROI was basically stable at60cm.(5) The groundwater circulation flowvelocity increased with the increment of the distance between upper and bottom tube,and the highest circulation velocity was up to28.60m/d.The remediation of NAPL contaminated aquifer by GCW was carried out in atwo-dimension sand tank. The mainly experimental results are:(1) the sorptionisotherm of benzene, nitrobenzene and naphthalene were linear models and theadsorption coefficient was affected by medium size and organic matter content.(2)The preferentially lateral was observed when organic compounds leaked intogroundwater as well as the longitudinal concentration diffusion, the time thatbenzene, nitrobenzene and naphthalene polluted the whole sand tank were30d,30dand50d, respectively.(3) After accumulated aeration time exceeded14h, benzenecan not be detectived in the groundwater, whereas the remove of nitrobenzene andnaphthalene entered the stage of tail and the tail concentration were71.19mg/L and1.82mg/L, respectively.(4) The relative average concentration of organic matter ineach column was negative to the log of the accumulated aeration time; concentrationattenuation of each column was decreased with the increment of the distancebetween each column and the GCW; benzene attenuation coefficient was higher thannitrobenzene and naphthalene.(5) The position of nitrobenzene and naphthaleneconcentration dropped fastest located in the left of the sand tank, and the S/Sowaspositive to the C/Cowhen C/Coof nitrobenzene and naphthalene ranged from0to 0.5.According to the mechanism of solubilization and mobilization, SDBS andTween80were selected and the investigation of sorption, lowering the surfacetension and solibilizaiton properties were carried out.(1) The sorption isotherms ofSDBS and Tween80in the medium sand were Langmiur model and Frundlich model,respectively. The highest saturated adsorption amounts were2.04and7.87mg/g.(2)the capability of reduce surface tension of Tween80was superior to SDBS.(3) Kmcof benzene, nitrobenzene and naphthalene in Tween80solution were4.44×103,4.38×103and1.52×103mL/g, that greater than Kmcin the SDBS solution.(4)Temperature and ion strength were positive to the solubilization of naphthalene inTween80solution, and the higher of the Tween80solution concentration, the greaterof the naphthalene apparent solubility.A one-dimension columns were utilized to study benzene, nitrobenzene andnaphthalene removal efficiency in groundwater with surfactant flushing, the mainresults are:(1) The critical flushing concentration of Tween80was2.0g/L.(2) Theremoval efficiency was increased by the increment of Tween80solutionconcentration, but the removal efficiency increase was not significant once theTween80solution concentration exceeded10.0g/L.(3) The removal efficiency canbe imporved with the increase of flushing velocity, but too higher flushing velocitymay decrease the removal efficiency.(4) Medium size has great effect on theremoval efficiency. Too small or to large size of the medium would both notconducive to the removal of organic matter.(5) Surfactant enhanced aquiferremediation would be not appropriate when the organic matter content was toohigher.According to the residual concentration of nitrobenzene and naphthalene,Tween80solution was used to enhance the removal efficiency of GCW. The mainresults are:(1) the preferentially longitudinal of Tween80solution was observed aswell as the lateral concentration diffusion.(2) The migration of Tween80in theaquifer can be controlled by GCW; Tween80concentration that higher than2.0g/L,which covered an area of more than80%of the contaminated aera distributed evently on both sides of GCW after aeration time exceeded14h.(3) Nitrobenzeneand naphthalene concentration in aqueous were greatly increased by surfactantsolubilization and the average concentration were up to147.07mg/L and3.62mg/L,but lower than solibilizaiton experimental results. The tail concentration ofnireobenzene and naphthalene decreased to41.43mg/L and0.69mg/L after aeration14h.(4) Concentration attenuation of nitrobenzene and naphthalene in each columnwas negative to the log of accumulated aeration time, and naphthalene concentrationattenuation was higher than naphthalene.(5) The position that nitrobenzene andnaphthalene concentration dropped fastest in the middle of the sand tank, and C/Cowas positive to S/Soas C/Corange from0to0.5.