From Tech Trends January 1993

Extraction Process Separates Organics from Sludges, Soils and Sediments

By Mark Meckes, Risk Reduction Engineering Laboratory

The Basic Extractive Sludge Treatment (B.E.S.T.) process is a solvent extraction system that uses triethylamine to separate organic contaminants from sludges, soils and sediments. The B.E.S.T. process was pilot demonstrated under the EPA's Superfund Innovative Technology Evaluation (SITE) program in cooperation with the Great Lakes National Program Office and the U.S. Army Corps of Engineers. The demonstration treated river bottom sediment from the Grand Calumet River in Gary, Indiana, which was contaminated with oil and grease, polychlorinated biphenyls (PCBs) and polynuclear aromatic hydrocarbons (PAHs).

The key to the success of triethylamine extraction is the property of inverse miscibility. At temperatures below 60 degrees Fahrenheit, triethylamine is miscible with water; above 60 degrees Fahrenheit, triethylamine and water are only slightly miscible. A triethylamine solvent chilled below 60 degrees Fahrenheit mixes well with water, thus attracting water and contaminants from solids, resulting in a non-homogenous mixture of moisture-free solids and a solution of solvated oil, water and solvent. This is referred to as "cold extraction." Later, during the "hot extraction," the organic contaminants that remain in the dewatered solids are removed by warm triethylamine, which is heated to temperatures ranging from 70 to 160 degrees Fahrenheit and above. Triethylamine moves contaminants from moisture-free solids more effectively at these higher temperatures. The B.E.S.T. process operates as follows. Contaminated material is screened to less than 1/2 inch diameter (1/8 inch for this demonstration) and added to a refrigerated premix tank with a predetermined volume of 50% sodium hydroxide. After the tank is sealed and purged with nitrogen, chilled triethylamine solvent is added. The chilled mixture is agitated and then allowed to settle, creating the non-homogenous mixture of moisture-free solids and the solution of solvated oil, water and solvent. The solution is decanted from the solids and centrifuged. The solvent and water are removed from the solvent/water/oil mixture by evaporation and condensation of the solvent and water. Solids with high moisture content may require more than one cold extraction. For example, for this demonstration, a sediment containing 41% moisture required two cold extractions.

Once a sufficient volume of moisture-free solids is accumulated, it is transferred to a steam jacketed extractor/dryer where warm triethylamine is added to the solids. The mixture is heated, agitated, settled and decanted to separate any of the organics not removed during the initial cold extraction. The solids remaining in the extractor/dryer contain triethylamine following decanting. A small amount of steam is injected to volatilize this remaining triethylamine. The hot extraction process can be repeated, when necessary, to further remove contaminants. The products from the process are: (1) solids, (2) water and (3) concentrated oil containing the organic contaminants. The recovered oil fraction can be dechlorinated or incinerated to destroy the organics. The triethylamine is recovered and reused in further extractions.

Two sediment samples were treated for this SITE demonstration. Sediment A contained 41% moisture, 6,900 milligrams oil and grease per kilogram of sediment (mg/kg), 12 mg/kg PCBs and 550 mg/kg PAHs. The process removed greater than 98% of the oil and grease, 99% of the PCBs and greater than 96% of the PAHs. Sediment B contained 64% moisture, 127,000 mg/kg oil and grease, 430 mg/kg PCBs and 73,000 mg/kg PAHs. The process removed greater than 98% of the oil and grease and greater than 99% of the PCBs and PAHs. The residual solvent in the process' products of solids, water and oil (Sediment B) was 103 mg/kg, less than 1 mg per liter and 730 kg, respectively.

For more information, call Mark Meckes at EPA's Risk Reduction Engineering Laboratory at 513-569-7348. A Technical Evaluation Report and an Applications Analysis Report describing the complete demonstration will be available in the summer of 1993.