Fate And Transport Of Typical Organic Pollutants In Saturated Porous Media

With the rapid development of chemical industry in China,bisphenol A(BPA)/bisphenol S(BPS)and organic solvents are widely used in plastics production and other various industries.They released into soil and groundwater by various ways.The pollutant imposed threats to the safety of drinking water and public health.Therefore,how to predict the fate and transport of organic in the subsurface media is of great significance for their risk assessment and remediation.However,the transport of organic pollutants were affected by the complex geological environment,pollutant characteristics,hydrochemical and hydrodynamic conditions,and combined pollution(dissolved organic matter and non-aqueous phase liquids(NAPLs)),and it is still not clear.In this study,laboratory experiments(adsorption batch experiments,1-D column experiments,2-D sandbox experiments)and mathematical modeling were conducted to study the retention and transport of organic(BPA,BPS,tetrachloroethylene(PCE)and Xylene)in water saturated porous media.The effects of different aqueous media(type,particle size),water chemical conditions(ion type,ionic strength),hydrodynamic conditions(flow rate),combined pollution state(dissolved phase organic and NAPLs)on their retention and transport were systematically investigated.And their transport behavior and impact mechanism were explored.This research could provide evidence and reference for accurately predicting the transport and distribution of organic pollutants.The mainly results of this paper are showed as follows:1)BPA and BPS have strong mobility in quartz sand media,and their breakthrough curves(BTCs)results are close to the results of the tracer.Their mass recvoery rate are higher than 99.17%.The pollution concentration,ion type,ionic strength,particle size and flow rate have nearly no influence on their mobility.For that the quartz sand media has a single component and smooth particles,which have little adsorption to the BPA/BPS.The one-site kinetic model can describe the transport of BPA/BPS well.2)In the limestone porous media,the mobility of BPA and BPS is lower than that in sand porous media.For that the limestone medium is mainly carbonate,contains a small amount of organic matter,and the surface of the particles is rough,which makes more BPA/BPS be adsorbed and retained.The mobility of BPS is significantly stronger than that of BPA in limestone media.For that the difference molecular structure of BPA and BPS,the limestone porous media has a weaker adsorption capacity for BPS than BPA which was more hydrophobic.With the input concentration of BPA decreased,BPA showed lower mobility;while the transport of BPS in the media was not affected by its input concentration.The retention of both BPA and BPS was higher in divalent calcium ion solution than that in monovalent sodium solution.Ionic strength showed little effect on the retention and transport of BPA and BPS except that a high concentration of Ca2+inhibited the mobility of BPS.For that ionized calcium bridges and enhance electrostatic when more the divalent calcium ion present in the solution,which could produce adsorption,and inhibit the mobility of BPA and BPS,especially the BPS was mainly in the ionic state.With the particle size of limestone or the groundwater flow rate increased,the mobility of BPA/BPS could be promoted.The two-site kinetic model can describe the transport of BPA/BPS well.3)In the three different natural soils,BPA and BPS had high mobility in saturated soil A(Xinjiang sandy soil),medium mobility in soil B(Changshu paddy soil)media,and no mobility in the soil C(Jilin black soil).There was a negative correlation between the mobility of BPA/BPS and soil organic matter(SOM)content because of the strong sorption of BPA/BPS on SOM.BPS showed higher mobility than BPA in the three soils.In addition,with the reduction of SOM of the soil B and C(after H2O2-treatment),the mobility of BPA/BPS enhanced dramatically.All these suggest that SOM played a significant role in controlling the retention and transport of BPA/BPS in the soil.While other factors of soil media properties(e.g.particle size and specific surface area)have a limited effect on the mobility of BPA and BPS.Furthermore,the two-site kinetic model simulated the BPA/BPS transport experiment results very well.4)The mixing volume ratio of NAPLs and heterogeneity of media affect the migration and distribution of mixed NAPLs.In the homogeneous media,when Xylene:PCE<8:2(V:V),the mixed NAPLs migrate downward as the properties of DNAPL,and as the mixing ratio decreases,its migration speed increased,and the accumulation at the bottom aquifer increased;when Xylene:PCE>8:2,they migrated upwards as LNAPL,and as the mixing ratio increases,the migration speed increases and the accumulation in the top aquifer increased;while Xylene:PCE=8:2,the mixed NAPLs migrated around the pollution source,and its distribution range is limited.In the heterogeneity media,the experiment results showed that the mixing volumn ratio of NAPLs and heterogeneity of media common effect the migration of the mixed NAPLs.The coarse media promote the transport of the mixed NAPLs and form discontinuous residual NAPLs(ganglia),and the fine media inhibited mixed NAPLs and accumulated to a pool.5)In the subsurface environment,the presence of trapped NAPLs has an important influence on the migration of BPA and BPS.In the aqueous-NAPLs-solid phase multiphase system,the retention and migration of BPA and BPS are cooperatively controlled by the characteristics of residual NAPLs,types of media,the characteristics of contaminants.Residual NAPLs inhibited the transport of BPA in sand and soil A columns,and the inhibiting effect of Xylene was greater than that of PCE.While the presence of NAPLs showed little influence on the transport of BPS in the sand and soil A columns.The adsorptionn of BPA follow the sequence:Xylene>PCE>sand/Soil A,and BPS was little adsorbed by them.The presence of residual NAPLs reduced the retention of BPA/BPS in the limestone and soil B columns because the NAPLs blocked the sorption sites of the limestone and soil organic matter for BPA/BPS.Therefore,NAPLs promote the migration of BPA/BPS,and the promoting effect of PCE is greater than that of Xylene.In addition,the oil-wet residual NAPLs in Soil A enhanced the inhibition of BPA transport,and had little influence on BPS,while in Soil B,the migration promotion of BPA and BPS were enhanced.