| Chlorinated hydrocarbons are one of the most widespread pollutants in the world.They have "tri–causal" effects,are difficult to degrade,have low water solubility,and are easily migrated to aquifers when they are leaked into the underground environment.In addition,due to the high O/W interfacial tension and low water solubility of chlorinated hydrocarbons and aquifer media,they are easily retained in the pores of the media and are difficult to be removed,thus causing the problems of time–consuming,low efficiency and high cost in the remediation of underground chlorinated hydrocarbon pollution.Surfactant–enhanced remediation(SER)technology increases the solubility of chlorinated hydrocarbons in water through micelle solubilization,which can rapidly remove them from aquifer media,and the selection of suitable surfactants is the key to the application of this technology.Most of the surfactants used in last decades are traditional single–chain surfactants,and the solubilization of pollutants is mostly one order of magnitude,and the biodegradability and environmental compatibility of the surfactants themselves are not considered enough,so it is important to develop surfactants with efficient solubilization ability and environmental friendly characteristics.An amino acid gemini surfactant,N,N’–dilauroyl ethylenediamine sodium dipropionate(DLMC),was used to solubilize chlorinated hydrocarbons represented by tetrachloroethylene(PCE).Static solubilization and column flushing experiments showed that DLMC and its co–mixed systems had good solubilization performance on PCE.The effects of flushing solution injection rate,media size and PCE residual saturation on the flushing effect of DLMC and its co–mixed systems on PCE removal were investigated by orthogonal experiments.The main conclusions are as follows.(1)DLMC has good surface properties,anti–ionic properties,anti–adsorption properties and low viscosity,but DLMC does not have the ability to withstand low temperature,and the compounding with short–chain alcohols or non–ionic surfactants can improve the surface activity at low temperature.The biodegradability was over 99%.(2)DLMC showed the best solubilization performance for PCE,with the aqueous phase concentration of PCE reaching 16047 mg/L,WSR reaching 0.45 and MSR reaching 1.67 at a surfactant concentration of 40 g/L.(3)Among the co–mixed systems of DLMC,DLMC–Tween80(1:1)has the best solubilization performance on PCE.The aqueous phase concentration of PCE at 25 ℃ and 10 ℃ reached 16906 and 11813mg/L respectively at a surfactant concentration of 40g/L,and the flushing efficiency of PCE reached 9.87 g PCE per liter flushing solution,which is 77 times higher than that of water,and 16% higher than that of single DLMC system.(4)The flushing process of DLMC and its co–mixed system on residual phase PCE contaminated column can be divided into three stages,of which the first stage is the high efficiency stage.The influences on the flushing efficiency of the first stage are in the following order: injection rate>media size>PCE residual saturation>surfactant system;the influences on the cumulative flushing removal rate are in the following order: injection rate>PCE residual saturation>surfactant system>media size.(5)With the same residual saturation of PCE,the higher the flushing efficiency of the first stage,the higher the cumulative removal rate.the best formulation of DLMC and its compound system is DLMC–Tween80(1:1)system;the best injection rate is 1m L/min;it has better flushing effect for sites with lower residual saturation and larger porosity. |
