Integrated system for remediation of contaminated soils

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) bio treatment of the contaminant residual. Pilot-scale countercurrent solvent w ashing was carried out using a 95% ethanol solution -a solvent that in an e arlier bench-scale study was found to be effective in removing PCP and hydr ocarbons (HCs) from soils. Three-stage countercurrent solvent washing of a field-contaminated soil was performed using batches of 7.5 kg of soil and 3 0 L of solvent (1 kg:4 L soil-to-solvent contact ratio). The washed soil wa s rinsed with water in a single stage after three countercurrent wash stage s. Pilot-scale, three-stage countercurrent solvent washing with 95% ethanol reduced the PCP and HC contamination on the soil by 98 and 95%, respective ly. 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 th e 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 ca ptured in the bottoms stream. The bottoms stream was treated sequentially i n anaerobic and aerobic granular-activated carbon fluidized-bed reactors. C omplete mineralization of PCP was achieved using this treatment train.