Solvent extraction treats sludges, sediments, and soils contaminated with a wide range of hazardous contaminants including polychlorinated biphenyls (PCB), polynuclear aromatic hydrocarbons (PAH), pesticides, and herbicides. The waste matrix is separated into three fractions: oil, water, and solids. Organic contaminants, such as PCBs, are concentrated in the oil fraction, while metals are separated into the solids fraction. The volume and toxicity of the original waste is thereby reduced, and the concentrated waste streams can be efficiently treated for disposal.
The B.E.S.T. technology is a mobile solvent extraction system that uses secondary or tertiary amine solvents to separate organics from soils, sediments, and sludges. The B.E.S.T. solvents are hydrophobic above 20 °C and hydrophilic below 20 °C. This property allows the process to extract both aqueous and nonaqueous compounds by changing the solvent temperature.
Pretreatment includes screening the waste to remove particles larger than 1 inch in diameter, which are treated separately.
The B.E.S.T. process begins by mixing and agitating the solvent and waste in a mixer/settler. Solids from the mixer/settler are then transferred to the extractor/dryer vessel. (In most cases, waste materials may be added directly to the extractor/dryer and the mixer/settler is not required.) Hydrocarbons and water in the waste simultaneously solubilize with the solvent, creating a homogeneous mixture. As the solvent breaks the oil-water-solid emulsions in the waste, the solids are released and settle by gravity. The solvent mixture is decanted from the solids and centrifuged to remove fine particles.
The solvent-oil-water mixture is then heated. As the mixture's temperature increases, the water separates from the organics and solvent. The organics-solvent fraction is decanted and sent to a solvent evaporator, where the solvent is recycled. The organics are discharged for recycling, disposal, or treatment. The water passes to a steam stripping column where residual solvent is recovered for recycling. The water is typically discharged to a local wastewater treatment plant.
The B.E.S.T. technology is modular, allowing for on-site treatment. The process significantly reduces the organic contamination concentration in the solids. B.E.S.T. also concentrates the contaminants into a smaller volume, allowing for efficient final treatment and disposal.
The B.E.S.T. technology can remove hydrocarbon contaminants such as PCBs, PAHs, pesticides, and herbicides from sediments, sludges, or soils. System performance can be influenced by the presence of detergents and emulsifiers.
The B.E.S.T. technology was accepted into the SITE Demonstration Program
in 1987. The SITE demonstration was completed in July 1992 at the Grand
Calumet River site in Gary, Indiana. The following reports are available
from EPA:
The first full-scale B.E.S.T. unit was used at the General Refining Superfund site in Garden City, Georgia. A 75-ton-per-day B.E.S.T. unit is being installed at Idaho National Engineering Laboratory to extract organic contaminants from mixed wastes.
The SITE demonstration showed that the B.E.S.T. process removed greater than 99 percent of the PCBs found in river sediments without using mechanical dewatering equipment. Treated solids contained less than 2 milligrams per kilogram PCBs. Comparable removal efficiencies were noted for PAHs.
EPA PROJECT MANAGER:
Mark Meckes
U.S. EPA
National Risk
Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7348
Fax: 513-569-7328
TECHNOLOGY DEVELOPER CONTACT:
William Heins
Ionics/Resources
Conservation Company
3006 Northup Way, Suite 200
Bellevue, WA
98004
425-828-2400
Fax: 425-828-0526