Use of preformed microemulsions

Preformed micro emulsions can also be used for soil decontamination. The application of bioremediation with microemulsions containing nutrients for oil spills is already a well-known technology [84, 85] and is also proposed for in situ treatment of DNAPL sites [86]. Studies on contaminant extraction, however, are less frequent. In most cases, these systems have been discussed and investigated for adsorbed or highly viscous contaminants which can only be solubilised. Enhancement of solubilisation in micro emulsions compared with surfactant solutions was found for pyrene [87] and patented for ex situ treatment of contaminated soil [88]. An interesting cost-effective variation uses partially sulphated castor oil [89]. 

W/o-droplet microemulsions with non-ionic surfactants containing rapeseed oil methyl ester have been successfully used for in situ extraction of polycyclic aromatic hydrocarbons [40]. However, enhancement of oil content and solubilisation capacity failed with these systems. The use of co-surfactants and co-solvents for suppression of liquid crystal formation was considered to be critical for in situ application. 

A complex system containing a branched anionic surfactant, non-ionic surfactants, rapeseed oil methyl ester and an aqueous calcium chloride solution was found to form bicontinuous microemulsions even at low temperatures [46, 90]. This type of microemulsion has been studied for DNAPL extraction on a large scale in an artificial aquifer and later in a joint project with different partners financed by the German Federal Ministry of Education and Research (BMBF) [91 ]. The project network applied an integrated concept regarding aspects of hydraulics, reuse and biodegradation [92]. Three large-scale experiments each with some hundreds of litres of preformed microemulsion were performed. Whereas extraction of perchloroethylene in the field-scale experiment was not successful 

Preformed microemulsions containing co-solvents and co-surfactants have been used for laboratory experiments [94] and a field test [55] in Canada. The systems were developed for the extraction of a viscous oil containing up to 16% of chlorinated solvents from a site at Ville Mercier. The contaminant is a DNAPL with a density of 1.05 g/cm3 and thus exhibits only a small density difference compared to chlorinated solvents [94]. It could not be extracted effectively by the usual Winsor I systems containing n-butanol as a co-surfactant. The addition of solvents was necessary for effective solubilisation of the contaminant [94]. A preformed microemulsion containing D-limonene, toluene, n-butanol, Hostapur SAS (secondary alkane sulphonate sodium salt) and water was injected into a field test site at Thouin Sand Pit near Montreal. In previous column experiments, a composition of 13.16% D-limonene, 13.16% toluene, 9.21% n-butanol, 9.21% Hostapur SAS and 0.3% of sodium ortho-silicate in water was used as a preformed microemulsion for the extraction of DNAPL from Ville Mercier. 

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