The Research On The Transport Characteristics Of Surfactant-hydrophobic Organic Compounds Aggregate In Porous Medium

Surfactant enhanced aquifer remediation(SEAR)technology have been studied and applied widely in remediating the hydrophobic organic compounds(HOCs)contaminated aquifer.This technology is based on two mechanisms: Firstly,the flushing of surfactant solution enhances the mobilization of HOC s in the form of NAPL;Secondly,the flushing the surfactant can enhance the apparent solubility of HOCs based on the formarion of surfactant micelle.The surfactant micelle solubilization not only enhancen the solubility of HOCs,but also enhance the bio-availability of HOCs.Large quantity of surfactant-HOCs aggregate will occur in aquifer during the application of SEAR technology and these aggregats will transport in the aquifer.These aggregats may be intercepted,adsorpd and aggregate when they transport in aquifer.At the same time,transport characteristics of these surfactant-HOCs aggregates will impact on the recovery and final treatment of pollutants in SEAR technology.The soil-groundwater environment is a complex system and the transport process of surfactant-HOCs aggregates is affected by the characteristics of aquifer medium,hydraulic conditions,ionic strength and organic matter content.However,few studies have been paid on the characteristics of surfactant-HOCs aggregates and the transport of surfactant-HOCs aggregates in porou medium.Therefore,this paper focuses on the transport characteristics of surfactant-HOCs aggregates formed by surfactants and HOCs in saturated porous media and the main contents include the following three sections:In the first section: The solubilization of dodecane by batch solubilization and onedimension flow column experiments are studied with two surfactant — di RL and SDBS.The results showed that di RL and SDBS enhance the solubilization of dodecane at both below CMC and above CMC in batch solubilization experiments;what’s more,the molar solubilization ration is higher at below CMC than at above CMC,whiche is probably due to the formation of premicelle aggregate.On the basis of batch solubilization experiments,we studied the effect of surfactant flushing on the mobilization and solubilization of residual saturation dodecane in porous medium packed column.The results showed that the mobilization of dodecane in the form of NAPL was fast under the flushing of surfactant solution.Furtherly,we investigated the effect of flow velocity,concentration of surfactant,size of porous medium and roughness of porous medium surface on the flushing solubilization dodecan e in porous medium.The experiment results indicated that,the solubilization of dodecane by surfactant micelles is a rate-limited process.The solubilization of dodecane is increased with the decrease of porous medium size.What’s more,the concentration of solubilized dodecane is higher in poruos medium packed column with rougher surface.In the second part: Transport of surfactant-dodecane aggregate formed by di RL,SDBS,TX-100 and CPC with dodecane are investigated through one-dimension fow column experiment.The effect of porous medium,flow velocity and ionic strength on the transport of surfactant-dodecane aggregates.The results indicated zeta potential and size of aggregate played an important role in transporting of aggegate in porous medium packed column.Due to the negative zeta potential of porous medium surface used in the experiment,the three surfactant-dodecane aggregates of di RL-dodecane,SDBSdodecane,and TX-100-dodecane aggregate with negative zeta potential exhibit good transport characteristics relatively.The CPC-dodecane aggregate was interceppted in the column because of the positive zeta potential.The experimental conducted under different flow rates showed that different surfactant-dodecane aggregates exhibited different degrees of rention in the porous media column at low flow rates.In addition,results showed that the aggregates size had obvious influence on the retention of aggregate in porous medium column.The strong Brownian motion of SDBS-dodecane aggregate caused more obvious retention in column experiments due to the smallest particle size of aggregate among three surfactant-dodecane aggregate of di RL-dodecane aggregate(125.6 nm),SDBS-dodecane aggregate(6.1 nm),and TX-100-dodecane aggregate(108.1 nm).In addition,the results showed that the increase of ionic strength inhibited the migration of surfactant-dodecane aggregate particles in porous media column,and the divalent cations show more significant inhibitory effect than the monovalent cations.In the third section: The transport of surfactant-toluene aggregate in porous medium packed column is studied.The results showed that the size of both TX-100-toluene aggregate and SDBS-toluene aggregate is less than 10 nm.The strong brownian motion enhance the collision of aggregate to the porous medium surf ace,which result in the retention of TX-100-toluene aggregate and SDBS-toluene aggregate in the column transport experiment.Comparing the breakthrough curve between TX-100-dodecane aggregate and TX-100-toluene aggregate in column transport experiment,we can conclude that the size of aggregate play an important role in affecting the transport of surfactant-HOCc aggregate.In the fourth part: Transport of surfactant-dodecane aggregate in natural sediment is investigated.In this section,the transport of di RL-dodecane aggregate,SDBSdodecane aggregate and TX-100-dodecane aggregate in natural sediment packed column.Results showed that obvious retention of three surfactant-dodecane aggregates occurred in the column transport experiment.This is because the smaller particle size and heterogeneity of sediment,which makes more aggregate particles can be attached to the sediment surface.At the same time,the partitioning of dodecane in aggregate into soil organic material caused the distinct difference of dode cane breakthrough curve and surfactant breakthrough curve.Due to the partitioning of TX-100 into soil organic material,the breakthrough curve of TX-100-dodecane aggregate different from the breakthrough curve of di RL-dodecane aggregate and SDBS-dodecane aggregate.Result also indicated that the increase of flow velocity enhanced the surfactant-dodecane aggregate transport in natural sediment column.These results indicate that the heterogeneity and the existence of SOM affect the transport of surfactant-HOCs aggregate obviously.