Surfactant enhanced aquifer remediation application

Microemulsions became well known from about 1975 to 1980 because of their use in "micellar-polymer" enhanced oil recovery (EOR) (35). This technology exploits the ultralow interfacial tensions that exist among top, microemulsion, and bottom phases to remove large amounts of petroleum from porous rocks, that would be unrecoverable by conventional technologies (36,37). Since about 1990, interest in the use of this property of microemulsions has shifted to the recovery of chlorinated compounds and other industrial solvents from shallow aquifers. The latter application (15) is sometimes called surfactant-enhanced aquifer remediation (SEAR). 

Dwarakanath, V. Pope, G.A. Surfactant Enhanced Aquifer Remediation in Surfactants, Fundamentals and Applications in the Petroleum Industry, Schramm, L.L. (Ed.), Cambridge University Press, Cambridge, UK,... 

As there are other less sophisticated and less expensive techniques available, surfactant-enhanced aquifer remediation will only be useful for decontamination of LNAPL sites in special cases. However, applicable techniques are still needed for DNAPL sites and microemulsion techniques are really promising. Therefore, most research has concentrated on this type of contaminant in recent years. Integrated concepts have been developed including aspects of soil properties [47, 48, 62, 63], density control [47, 48, 62-64], recovery and reuse of microemulsion components [47], biological degradation of residues of contaminants and injected compounds [48, 65] and costs [47, 48, 64, 65]. Two main approaches have been followed for developing effective surfactant systems which form microemulsions with DNAPL, but do not mobilise the liquid contaminant into deeper... 

The use of surfactants for remediation of contaminated soils and aquifers has been widely examined. Techniques for remediation are conveniently denoted as in situ and ex situ, where the former refers to treatment of soil or aquifers in place (in the subsurface) and the latter indicates excavation of soil for treatment above ground and pump and treat in the case of aquifers. The literature is quite extensive on surfactant-enhanced subsurface remediation [15] and has relied on the basics of surfactant-based remediation chemistry-physicochemistry-hydrology [16-27]. It was further demonstrated that the recovery and reuse of the surfactant (if applicable), is critical for maintaining the economic feasibility of this remediation technology applied [28],... 

Microemulsions, like micelles, are considered to be lyophilic, stable, colloidal dispersions. In some systems, the addition of a fourth component, a cosurfactant, to an oil-water-surfactant system can cause the interfacial tension to drop to near-zero values, easily on the order of 10 - 10 mN/m, allowing spontaneous or nearly spontaneous emulsification to very small drop sizes, 10 nm or smaller. The droplets can be so small that they scatter little light, and the emulsions appear to be transparent and do not break on standing or centrifuging. Unlike coarse emulsions, microemulsions are thought to be thermodynamically stable. The thermodynamic stability is frequently attributed to transient negative interfacial tensions, but this, and the question of whether microemulsions are really lyophilic or lyophobic dispersions are areas of some discussion in the literature. As a practical matter, microemulsions can be formed, have some special qualities, and can have important applications in areas such as enhanced oil recovery, soil and aquifer remediation, foods, pharmaceuticals, cosmetics, herbicides, and pesticides (13,16,45,59-61). 

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