Pilot-scale evaluation of an efficient salt-free in-situ microemulsion for the remediation of multiple halogenated hydrocarbons-contaminated aquifers.

Previous studies about aquifer flushing mainly focused on middle-phase microemulsions, which posed a risk of downward migration for dense non-aqueous phase liquids (DNAPLs). To address this limitation, our group developed a novel salt-free Winsor Type I microemulsion without the expansion risk of DNAPLs. However, it has not yet been applied at field scale, and the remediation efficiency for multiple DNAPLs remains to be fully evaluated. In this study, a mixture solution of 100 mM SDS and 10 % 1-butanol was injected into a multiple halogenated hydrocarbons-contaminated aquifer for flushing. Winsor Type I microemulsions were shown to form spontaneously in situ during the flushing process. The average particle size of extraction solution (50-100 nm) was consistent with the particle size of microemulsion. After 24 days of remediation, the maximum solubilisation concentration of TCE reached 13.3 times higher than initial concentration. The removal efficiencies for 1,1-DCE, 1,1-DCA, cis-1,2-DCE, 1,2-DCA, and TCE exceeded 75 %, and even VC was completely removed. Due to the absence of salt additives and the relatively low dosage of reagents in this microemulsion system, it would pose a low potential risk for secondary contamination. This pilot demonstration of in-situ microemulsion provided a highly efficient flushing technology and strategy for the remediation of DNAPLs-contaminated groundwater.