Approaches to the remediation of a polychlorinated biphenyl (PCB) contaminated soil - a laboratory study

A soil that had been historically contaminated with Aroclor 1242, 1248, 125 4 and 1260 was decontaminated by two surfactant-mediated cleaning procedure s that had been chosen to mimic ex-situ washing and in-situ soil flushing p rocesses. A preliminary screening selected four surfactants (from 17 commer cial formulations) for their ability to mobilise PCBs from the soil while s uffering minimal losses to the supercritical carbon dioxide (scCO(2)) that was used in a separate back-extraction procedure. The mobilisation was enha nced, with minimal foam formation, by the presence of 17% (v/v) IBMK in the surfactant suspension. Each of the four surfactants, at 1, 3, or 5% (v/v) concentration, was evaluated by (i) 15 successive 10 epsilon min sonication -filtrations and (ii) continuous soil column flushing during 20 h. Each fil trate from (i) and samples, taken at hourly intervals, from (ii) were analy sed for their PCB and surfactant content. Both extraction procedures mobili sed PCBs efficiently when extended for longer periods and were modelled acc urately as the sum of a constant and single-term exponential increase to a maximum. The predicted number of replicate stages required to mobilise 50% of the toxicants (t(50)) varied from 7 to 3 for sonication-washing of the s oil (10 g) or from 6.8 to 2.8 h for column flushing of 30 g soil and decrea sed as the concentration of surfactant in the aqueous phase was increased. The combined PCB-laden aqueous suspensions were then back-extracted efficie ntly with scCO(2) and the eluate was dechlorinated quantitatively as it tra versed a short, heated column of silver-iron bimetallic mixture.