Soil and sediment contamination has become an increasing problem in our industrial society. For nearly a hundred years, byproducts from various industries have been discarded in almost every place imaginable. The waste material was mearly dumped directly on the land or discharged into the water. Only recently have more stringent guidelines concerning wastes been addressed in a serious manner.
However, now the land and water that was polluted decades before is also considered to be a waste and must be dealt with according to EPA regulations. These contaminated soils and sediments need to be remediated in order to render them disposable.
One method for decontaminating sediments and soils is the use of a solvent extraction technique. In solvent extraction, an organic solvent is used to remove contaminants such as PCB's and PAH's. This method is a non-destructive process. The contaminants are simply concentrated in a form which is separate from the solids. The focus of this discussion will be on a selected solvent extraction technique for the removal of organic contaminants from soils and sediments.
Basic Extractive Sludge Treatment or B.E.S.T.® process is a technology which concentrates contaminants such as PCB's and PAH's into an oil stream. B.E.S.T.® stands for Basic Extractive Sludge Treatment and is a registered trademark of the Resources Conservation Company, Bellevue WA. The process renders the influent water and soil "clean" and supplies only a concentrated waste oil for disposal.
One of the keys of the B.E.S.T.® process is the use of Triethylamine as the solvent. Triethylamine has the interesting characteristic of being inversely miscible with water. At temperatures around 33°F, triethylamine is almost completely soluble. When the temperature of triethylamine exceeds 130°F, the solvent is not miscible and therefore separates from the solution.
The B.E.S.T.® process takes advantage of this characteristic by conducting subsequent extractions at different temperatures. In the first step, the triethylamine is cold and hence miscible with water. In the second step, the sample and triethylamine are heated above the miscibility limit; the phases separate. Nearly all the contaminants are trapped in a triethylamine/oil solution which is separate from the water and the solids.
The triethylamine/oil solution is then subjected to recovery techniques which recycle almost all of the triethylamine and produce only a concentrated oil.
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