Batch and Column Extraction Procedures for Organics in Solid Wastes

Abstract

Because of the possibility of contamination of aquifers by solid waste leachates, it is important to develop laboratory extraction procedures that predict the release of organic materials from landfills. This paper presents the results of a study comparing five laboratory extraction procedures with respect to the organic content of the extract. Nine solid wastes, representing a wide variety of matrices, were considered. The extraction procedures used were the Environmental Protection Agency Extraction Procedure (EPA-EP), a distilled water extractant, a citrate buffer extractant, a sodium ion-exchange resin extractant, and an upward-flow column extraction test. Organic analysis of the batch extracts was carried out by isolation/concentration of the leachates with XAD-2 resin, followed by gas chromatography on fused silica capillary columns. In the case of the upward-flow column extraction, a cartridge containing XAD-2 was placed directly at the column exit; the resin was isolated/concentrated in a manner identical to the batch extracts. The results were assessed both in terms of total chromatographable organics (TCO) and in terms of the levels of individual compounds. The column technique gave consistently higher results in terms of TCO. This effect is in large measure due to enhanced recovery of highly volatile compounds and nonpolar compounds. The results of the extraction of individual compounds were less consistent. The recovery of carboxylic acids, for example, depended primarily on pH. The recovery of volatile organics, on the other hand, was more closely related to the extraction vessel used than to the extractant. Thus, it may be concluded that the column procedure most aggressively extracted organics from the solid wastes. However, the chemical nature of the organic material in the solid waste determines which of the batch extraction procedures is most aggressive.