Integrated System for Remediation of Contaminated Soils

Abstract

A pilot-scale study was conducted to evaluate an integrated system for the remediation of soils contaminated primarily with pentachlorophenol (PCP), a wood preserver. The integrated soil remediation system consisted of three unit processes: (1) Soil solvent washing; (2) solvent recovery; and (3) biotreatment of the contaminant residual. Pilot-scale countercurrent solvent washing was carried out using a 95% ethanol solution—a solvent that in an earlier bench-scale study was found to be effective in removing PCP and hydrocarbons (HCs) from soils. Three-stage countercurrent solvent washing of a field-contaminated soil was performed using batches of 7.5 kg of soil and 30 L of solvent (1 kg:4 L soil-to-solvent contact ratio). The washed soil was rinsed with water in a single stage after three countercurrent wash stages. Pilot-scale, three-stage countercurrent solvent washing with 95% ethanol reduced the PCP and HC contamination on the soil by 98 and 95%, respectively. The spent solvent and the spent rinse water were combined as the spent wash fluid for further treatment. A pilot-scale distillation unit was used to recover the ethanol from the spent wash fluid. The HC constituents of the spent wash fluid were removed by pH adjustment prior to feeding the spent wash fluid to a distillation unit. Greater than 96% of the ethanol in the spent wash fluid was recovered in the distillate stream, whereas PCP was captured in the bottoms stream. The bottoms stream was treated sequentially in anaerobic and aerobic granular-activated carbon fluidized-bed reactors. Complete mineralization of PCP was achieved using this treatment train.