Cleaning up pesticide contaminated soils: Comparing effectiveness of supercritical fluid extraction with solvent extraction and low temperature thermal desorption

Bench-scale supercritical fluid extraction (SFE) studies were performed on soil samples obtained from a Superfund site that is contaminated with high levels of p,p'-DDT, p,p'-DDD, p,p'-DDE, toxaphene and hexachlorocyclohexane . The effectiveness of supercritical fluid extraction was assessed using pu re and modified CO2 as a solvent over a wide range of conditions. A 30-minu te extraction at 30 MPa and 80 degrees C was able to remove more than 98% o f the contaminants and reduce the contaminated volume by a factor of 500. S olvent extraction and thermal desorption treatability studies were conducte d on soil samples obtained from the same site to compare their performance with that of supercritical fluid extraction. A six-stage solvent extraction using methanol achieved 96 to 98% removal of the four contaminants, except for DDE which existed at low initial concentrations. The contaminated volu me reduction was 40 to 50 times. Low temperature thermal desorption employe d at 350 degrees C for 30 minutes removed more than 98% for each contaminan t except DDE. However, solvent extraction includes costly solvent regenerat ion and recycling steps, and thermal desorption generates air pollutants th at require expensive particulate removal and gas stream cleaning. This stud y attempted to show that SFE can be as effective as other emerging technolo gies in removing contaminants from soils, and can reduce the contaminated v olume by a large factor.