Research On The Migration And Transformition Mechenism Of Organic Contaminant With Colloids In Landfill Groundwater

With the rapid development of urbanization in China,the urban living garbage is increasing.And many of the landfills in our country belong to a simple landfill,it is formed on the basis of opencast stacking and natural ditch filling,and there is no professional impervious treatment at the bottom.These simple old living waste landfills will produce a lot of leachate in the course of years of operation,it contains a lot of organic pollutants,metal and heavy metal ions,inorganic salts,bacteria and viruses,and so on,characterized by high persistence and toxicity.At present,the problem of groundwater pollution in China is becoming more and more prominent,and the old living waste landfill has become one of the important sources of groundwater pollution.The colloid effect also promotes the migration and transformation of pollutants in this process.Based on the subject“Study on the risk assessment of organic pollution of groundwater in old landfill”,taking a landfill in Jilin as the research area.On the basis of hydrogeological survey,data collection and literature reading in the study area,the typical organic pollutants and typical colloids in the study area were selected.Study on the mechanism of migration and transformation of organic pollutants in shallow groundwater.In particular,the migration and transformation of organic pollutants and natural colloids have been studied.Indoor static test,dynamic simulation experiment and numerical simulation were carried out to reveal the migration and transformation rules of organic pollutants in shallow groundwater,and it provides a theoretical basis for pollution control of organic pollutants in groundwater.The research results show:1.the selection of typical pollutants and colloids:in the study area,13groundwater samples were collected from the landfill site,the upper and lower villages of the garbage dump,and 1 leachates from the landfill site.The collected water samples were analyzed and tested.The results showed that typical organic pollutants and typical colloids in landfill sites.The results of the test were found:the higher content of the samples is halogenated hydrocarbons and aromatic hydrocarbons.And the highest detection rate of aromatic hydrocarbons was benzene?50%?,the highest detection rate of halogenated hydrocarbons is trichloromethane?85.7%?.This study is directed at benzene that has a strong carcinogenic risk to the human body and the most common inorganic colloidal silica in the lithofacies aquifer system.Therefore,the typical organic pollutants in shallow groundwater of the study area were selected as benzene,and silica was chosen as the typical colloid.2.the physicochemical properties of silica colloids:In the absence of benzene and in the presence of benzene,the particle size and zeta potential?negative potential?of silica colloid increase with the increase of suspension pH.With the increase of IS,the size of silica colloid increases,and the zeta potential decreases.Compared the absence of benzene with the presence of benzene,the particle size of silica colloid increased,it is because silica colloid and benzene knot form larger particles.3.the transformition mechenism of organic contaminant with colloids:?1?the experimental results of adsorption kinetics showed that:when benzene and colloid coexist,the adding of silica colloids act as effective adsorption site of porous media and promoting the adsorption of benzene on porous media.The adsorption kinetics of three aqueous media?fine sand,medium sand and coarse sand?under the coexistence of benzene and colloid in the landfill and the single component benzene solution conforms to the quasi two order kinetic equation.The order of adsorption rate is fine sand>medium sand>coarse sand.Benzene has the fastest adsorption rate on fine sand and the slowest adsorption rate on coarse sand.And when the benzene and colloid coexist in shallow aquifer,the adsorption rate is greater than that of the single component benzene solution.The microscopic morphology of three kinds of media before and after adsorption was observed by scanning electron microscope.When benzene and colloid coexist,three kinds of medium particles are obvious before adsorption,and the pore is large,the surface gap of medium surface is smaller after adsorption,more compact,filling the pores of the pre adsorbed medium.It can be seen that silica colloids provide more adsorption sites and promote adsorption of more benzene.In addition,it can be seen from the results of X ray diffraction.The content of silicon and carbon elements increased obviously after adsorption.It is also indicated that the colloidal content of silica increases,thereby adsorbing more benzene.?2?the experimental results of adsorption thermodynamics show that:the adsorption thermodynamics of three aqueous media?fine sand,medium sand,coarse sand?in the landfill,the coexistence of benzene and colloid and the single component benzene solution conforms to the Langmuir adsorption model.The order of adsorption rate is fine sand>medium sand>coarse sand.Similarly,silica colloids act as adsorption sites to promote the adsorption of benzene on the medium.Benzene adsorption on the fine sand is the largest,and the amount of adsorption on the coarse sand is the least,and when the benzene and colloid coexist,the adsorption capacity is greater than that of the single component benzene solution.?3?the results of biodegradation experiments show that,the biodegradation of three aqueous media?fine sand,medium sand and coarse sand?in the landfill is in accordance with the first order decay kinetics model under the coexistence of benzene and colloid and the single component benzene solution.The attenuation rate is fine sand>medium sand>coarse sand.Benzene attenuates most rapidly on fine sand and slows down on coarse sand.Under the condition of coexistence of benzene and colloid.Compared of adsorption process that the concentration of benzene with time is not much lower than the single component benzene solution.The presence of silica colloid weakens the biodegradation of benzene.4.the migration mechenism of organic contaminant with colloids:?1?effect of different hydrochemical conditions on benzene migration in shallow aquiferWhen benzene and colloid coexist,With the increase of pH?pH=5,7,9?,the calculated natural attenuation constants are 0.33 d^-1,0.21 d^-1,0.46 d^-1 respectively,and the adsorption rate constants are 6.53×10^-2 cm³/g,8.37×10^-2 cm³/g and 1.12×10^-1cm³/g respectively,and the biodegradation rate constants are 0.012 d^-1,0.024 d^-1,0.005 d^-1 respectively.The rate constants of adsorption increased sequentially.This indicates that benzene is not easily adsorbed by medium in acidic environment.This is because in the acid environment,the surface polarity of the medium is enhanced,the hydrophilic ability of the medium is enhanced,the adsorption point of water is increased,and benzene is a hydrophobic organic matter,which leads to the reduction of the adsorption point of the medium to benzene,so the adsorption amount is reduced.This is because in the acid environment,the surface polarity of the medium is enhanced,the hydrophilic ability of the medium is enhanced,the adsorption point of water is increased,and benzene is a hydrophobic organic matter,which leads to the reduction of the adsorption point of the medium to benzene,so the adsorption amount is reduced.With the increase of ionic strength,the penetration ability gradually diminished and the adsorption capacity gradually increased.When there is no silica colloid,the penetration of benzene in the medium is weakened.It can be seen that the addition of silica colloid makes it occupy the adsorption sites on the surface of the medium,and promotes benzene migration in the medium.Although the presence of silica colloids in the process of adsorption provides more adsorption sites and increases the amount of adsorption,the adsorption process is not chemical adsorption,but a physical adsorption.The large particles synthesized by benzene and silica colloids are desorbed under the action of water flow,which leads to the enhancement of the penetration ability of benzene in the medium.?2?effect of different hydrodynamic conditions on benzene migration in shallow aquiferWhen benzene and colloid coexist,the penetration ability of benzene in aqueous medium increases with the increase of flow rate?V=0.1ml/min,V=0.2 ml/min,V=0.4 ml/min?.The natural attenuation rate constant are 0.25 d^-1,0.21 d^-1,0.04 d^-1,as the flow rate increases by calculation.The adsorption rate constants were 9.80×10^-2cm³/g,8.37×10^-2 cm³/g,2.24×10^-22 cm³/g respectively.The rate of biodegradation is0.077 d^-1,0.024 d^-1,0.012 d^-1,respectively.The natural decay rate constant and adsorption rate constant and the rate of biodegradation decrease with increasing flow velocity.This is because as the flow rate increases,the shear torque between benzene and the medium changes,and the shear force increases.On the other hand,with the increase of velocity,the residence time of benzene in the shallow aquifer is less,the diffusion of the solute is weakened,and the number of contact between the benzene and the medium is reduced.When there is no silica colloid,the penetration of benzene in the medium is weakened.It is also because silica colloids occupy the adsorption sites on the surface of the medium,thus facilitating benzene migration in the medium.5.the numerical simulation of benzene with colloidsA numerical model for the migration and transformation of coexistence of benzene and colloid and a single component benzene solution in shallow aquifers was established.The simulation results of breakthrough curve are close to experimental breakthrough curve results with colloid.The deposition rate coefficient of the coexistence of benzene and colloid is smaller(<4.45×10^-3/S),and the presence of silica colloid promotes the migration of benzene in shallow aquifers when the conditions are less than no colloids(<5.43×10^-3/S).