| In situ bioremediation of polychlorinated biphenyls (PCBs) has been the subject of considerable research since the early 1970's. Virtually every PCB bioaugmentation study to date has included manual mixing of the inoculum into the soil to allow for improved distribution of the PCB-degrading microorganism. Although a suitable solution to the problem of inoculum dispersal in the laboratory, it quickly becomes a serious dilemma when the technology is taken to the field. Thus, there is clearly a need to discover novel mechanisms for inoculum dispersal into the soil profile.; Chapter 1 of this dissertation provides a historical perspective with regard to PCB bioremediation research. Chapter 2 describes the discovery of a surfactant, sorbitan trioleate, which when utilized as a growth substrate a the PCB-degrading inoculum, can double the PCB degradation in soil as compared to identically treated soils without surfactant. The study further presents two plant-derived compounds, carvone and salicylic acid, as suitable PCB-degradation inducing substrates for the co-inoculum, Arthrobacter sp. st. B1B and Ralstonia eutrophus H850, respectively.; Chapter 3 provides a follow-up study that addresses the problem of inoculum transport. This study utilized 600 g of soil, which was packed into a PVC column. The earthworm Pheretima hawayana provided hands-off mixing of the soil profile during the study, while simultaneously affecting the indigenous microorganisms in such a way so as to allow for increased PCB degradation well beneath the soil surface, even in treatments that were not bioaugmented. The earthworms also improved soil aeration as shown by a methane diffusion study. Improved aeration potentially allowed for greater aerobic PCB degradation. The earthworms modified the soil ecology and are discussed as a possible factor in assisting in the remediation of PCB-contaminated soils. These data suggest that the addition of multiple PCB-degraders, surfactants, natural inducing compounds, and earthworms may be an integrated program, which allows practical and effective in situ bioremediation and that requires little maintenance, machinery, or money. |
