An integrated treatment methodology for PCB-contaminated soil

Abstract

This study proposed coupling two different treatment technologies, chemical dehalogenation using potassium polyethylene glycol (KPEG) and bioremediation, to optimize the destruction and detoxification of PCB-contaminated soil. Changes in toxicity over time were monitored through the use of the Salmonella/microsome assay and the E. coli prophage induction assay. In order to examine the efficacy of integrating chemical dehalogenation and bioremediation, a greenhouse (microcosm) study was conducted. Three different treatment conditions were examined in the study: (1) chemical dehalogenation by KPEG; (2) inoculation with PCB-degrading bacteria (Alcaligenes eutrophus H850); and (3) chemical dehalogenation with inoculation of PCB-degrading bacteria. Samples were taken at day 0, 90, and 180. Changes in the composition of specific PCB congeners (one trichlorobiphenyl, two tetrachlorobiphenyls, two pentachlorobiphenyls, and one heptachlorobiphenyl) were monitored by gas chromatograph-electron capture detection following treatment. The toxicity of residual PCB congeners following treatment was monitored using the Salmonella/microsome and E. coli prophage induction bioassays. Data collected in this study include solvent extractable organics for untreated and treated soils, biological test data for the two microbial genotoxicity assays, and PCB concentrations for the six congeners being monitored. Results indicated that KPEG was not appreciably degraded in the soil as 69% more residue was extracted from the samples treated with KPEG than from the sterile control soils at day 0 and day 180. There was no decline in total solvent extractable organics in the sterile control soils or the KPEG treated soils over the study period. The soils receiving bacterial treatment alone did show decreases in extractable organics over time, with the exogenous bacterial treatments showing a decrease in extractable organics of 29% and the indigenous treatment showing a decrease of 43% over the study period. The genotoxicity of the soil for all treatment conditions was unchanged over the study period. All samples from treated soils were non-genotoxic in both bioassays at all sampling times. The PCB concentrations in the KPEG treated boxes did show a slightly higher level of PCB degradation than their non-KPEG treated counterparts. No decrease in the concentrations of the two pentachlorinated biphenyls was seen in the soils treated with bacteria only. Based on these results, KPEG did not appreciably enhance the degradation of PCBs under the conditions used in this study. Further research on the optimal parameters for KPEG dehalogenation are needed in order to make this a feasible method for the destruction of PCBs in soil.