| Groundwater,as an important source of drinking water,once contaminated by organic matters,will seriously threaten the ecological environment and human health.Therefore,restoration of organic contaminants in groundwater is crucial to the sustainable development of the ecological environment and human health.Due to the complexity of hydro-geological conditions and the heterogeneity of real aquifer,the transport process of organic contaminants in heterogeneous aquifer is extremely complicated.Therefore,the research on transport and remediation of organic contaminant in heterogeneous aquifer have focused on hot points and difficulty problems.The previous research mainly focused on transport and remediation of organic contaminant in homogeneous aquifer.The objectives of this paper are to study transport process and mechanism for NAPLs contaminated groundwater in heterogeneous aquifer,to investigate remediation methods for NAPLs contaminated groundwater in heterogeneous aquifer in indoor conditions.Firstly,in order to study the influence of heterogeneous aquifers on the transport characteristics of organic contaminants in groundwater,in the paper author has studied the adsorption characteristics of sandy aquifer on organic contaminants in groundwater.Two light non-aqueous liquids,MTBE and toluene(TOL)were used as typical organic contaminants in groundwater,and the adsorption ability for the two contaminants by three sandy media(coarse,medium and fine sand)were investigated by adsorption kinetics and isothermal adsorption experiments.The results showed that all the three kinds of the sandy media had a certain adsorption capacity for MTBE and TOL,the order of adsorption capacity was fine sand>medium sand>coarse sand,theadsorption process conformed to the pseudo second-order kinetic model,and the adsorption isotherm complied with the Langmuir model.Secondly,MTBE was chosen as the typical NAPLs,and different sand columns were filled with different sandy media to form different heterogeneous porous media,which could simulate the layered heterogeneous groundwater aquifers.Mewhile,one-dimensional MTBE dissolved phase transport mathematical model was combined to study the transport of MTBE in different heterogeneous aquifers.The results suggested that MTBE had a lower transport rate in homogeneous sand than NaCl.In different combinations of heterogeneous media,the growth rate and breakthrough time of MTBE concentration were both different.The MTBE transport process was highly dependent on the heterogeneity of the porous medium with a significant delay and tailing phenomena of breakthrough curve compared to the transport in the homogeneous medium.In addition,numerical simulation on MTBE transport process in two heterogeneous groundwater porous media was conducted according to the contamination transport column experiments,and also solute transport model was established and its boundary conditions were set.After rating the parameter by the test difference method,the model can effectively simulate the transport process of MTBE in the heterogeneous media.Thirdly,zero-valent iron/biochar(ZVI/BC)and iron-copper/biochar(Fe-Cu/BC)composite reaction media were used as potential fillers for PRB to remove typical organic contamination in simulated groundwater.(1)the MTBE and chlorobenzene(CB)in the water were removed by using the ZVI/BC composite reaction medium,which was conducted with different initial pH,iron-carbon ratio,initial MTBE concentration and reaction time.The results revealed that the removal rate of MTBE in the ZVI/BC composite reaction medium was only 30.2%,indicating that the micro-electrolysis reaction could not effectively remove MTBE in water.When the initial concentration of chlorobenzene was 33.68mg/L,the initial pH was 2,the mass ratio of iron to carbon was 2:1,and the reaction time was 4 h,the highest removal rate of chlorobenzene could reach 99.6%.The CB removal process conformed to thefirst-order reaction kinetics model.Secondly,due to the Cu catalysis,the removal efficiency of chlorobenzene by Fe-Cu/BC composite reaction medium was significantly higher than that in the absence of Cu.The degradation of chlorobenzene in this system also conformed to the first-order reaction kinetics model.However,the Cu content in the system should not be too high,otherwise it will shorten the service life of the composite reaction medium.Finally,a series of combined PRB column experiments were designed to study the treatment effect of chlorobenzene in groundwater by Fe-Cu/BC composite reaction medium,including homogeneous and heterogeneous groundwater systems,to investigate the influence of the heterogeneity of natural aquifers on PRB remediation of organic contaminants in groundwater.In addition,the monitor of the effluent CB concentration of transport process of CB in homogeneous and heterogeneous sandy columns systems were carried out.Simultaneously,the changes of iron ion concentration and pH value in the effluent were monitored,and the intermediate and final products in different periods were analyzed to discuss the degradation mechanism of CB in composite reaction medium.The results showed that the average concentration of chlorobenzene in the effluent from the heterogeneous system was slightly lower than that in the efflent from the homogeneous system,and the time when the concentration of iron ions peaked was slightly earlier than that in the homogenized system.The degradation of chlorobenzene by Fe-Cu/BC composite reaction medium involved micro-electrolysis,catalysis and adsorption.Among them,micro-electrolysis contributed the most to the total removal of chlorobenzene by the system,followed by Cu catalysis,and the adsorption is the smallest.Compared to anaerobic conditions,Fe-Cu/BC composite reaction media could achieve higher chlorobenzene removal efficiency under aerobic conditions,and CB could be completely transformed into non-toxic substances.Therefore,for PRB remediation of CB in the actual groundwater,it is suggested to introduce an appropriate amount of oxygen. |
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