Biotransformation of PCBs in Contaminated Sludge: Potential for Novel Biological Technologies

Abstract

In this study, the biological transformation of polychlorinated biphenyls (PCBs) was investigated in sludge from the Ralston Street Lagoon (RSL), a United States Environmental Protection Agency (USEPA) designated Toxic Substances Control Act (TSCA) site, in Gary, IN. A biological tilled soil reactor (BTSR) operating under cycling anaerobic-aerobic conditions and vermicomposting bioreactors (VBs) inoculated with Eisenia foetida earthworms were both systematically investigated. Sludge heavily contaminated with PCBs (> 500 ppm PCB as Aroclor 1248) was loaded into the BTSRs and amended sequentially with PCB-dechlorinating anaerobic sediments and then aerobic PCB biodegrading microbes. The VBs were loaded with sludge mixed in varying ratios with sterile soil and then inoculated with earthworms. Bioreactors were monitored for the duration of the studies (ranging from four to nine months) and samples were regularly removed, extracted and analyzed for PCB congener content. Appropriate biotic and negative abiotic controls were maintained under the various conditions to quantify and measure the biological transformation of the PCB's. All samples were analyzed for PCB congener concentrations by Soxhlet extraction followed by gas chromatography with electron capture detection (ECD). In the BTSRs loaded initially with 500 ppm of PCBs, a 75 % reduction of total PCB was obtained while the BTSR loaded with 140 ppm PCBs revealed only a 25 % reduction in total PCB level. Sample analyses from the VBs demonstrated total PCB reductions ranging from 55 to 66 %, although worm-free control reactors showed PCB attenuations from 48 to 68 %. Analysis of earthworms showed an increase in PCB levels in the earthworm biomass, with concentrations reaching as high as 313 ppm. Mass balance analysis of the VB results demonstrated that most of the PCBs were bioaccumulated, although some PCB elimination was demonstrated. The results from both the anaerobic-aerobic cycling BTSR and VB investigations demonstrate potential for application for site clean-up and possible bioremediation of the Ralston Street Lagoon sludge.