Thesis Abstracts 2004
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Bioremediation of Polychlorinated Biphenyl (PCB) Contaminated Soil Using a Sequential Bioreactor
By: Delta Dawn Norum (MASc. - Environmental Engineering)
Supervisors: Dr. Kenneth J. Reimer and Dr. Barbara A. Zeeb
Abstract
The production of polychlorinated biphenyls (PCBs) was banned in North America in the late 1970’s yet three decades later there are still many PCB contaminated sites in existence. The development of new and innovative bioremediation strategies offers a potential solution for the clean up of these contaminated sites. Sequential bioremediation, a two-step anaerobic/aerobic process, currently being studied has shown to be a promising method for the complete and natural degradation of PCBs in soil.
The objectives of this thesis were to: i) scale up previous aerobic laboratory-scale experiments to the bench-scale; ii) reproduce the success of an anaerobic pilot-scale experiment using different soil (from Stephenville, Newfoundland); iii) improve sampling methods to obtain more representative samples; and iv) combine scaled up anaerobic/aerobic steps for complete PCB treatment.
Anaerobic bench-scale experiments were conducted to determine if it was possible to reintroduce dormant anaerobes from previous experiments into new dechlorinating environments. These anaerobic carboys (11 L) were also used to determine if soil from Stephenville, Newfoundland could be successfully dechlorinated in preparation for larger pilot-scale work. A change in congener profile was observed with a 35% average decrease in higher chlorinated PCBs indicating that the dormant anaerobes had been successfully reintroduced and the new soil could be dechlorinated. Anaerobic pilot-scale bioreactors (205 L) showed similar trends with a significant shift in the congener profile over thirty-eight weeks, with the average number of chlorine substitutions per PCB molecule decreasing from 6.5 to 4.4.
Aerobic bench-scale experiments showed no degradation occurring over the twenty-one week duration. Factors such as low bioavailability of the remaining PCBs, inhibitors in the soil preventing degradation and lack of growth of the inoculating cultures were investigated to determine the cause. Microbial testing showed that the inoculating cultures were thriving, so aerobic laboratory-scale microcosm experiments (15 mL) were conducted. Soil-washing and the addition of a surfactant (Biosolve®) were used as a means of minimizing or negating the impact of inhibition and/or low bioavailability. After a twenty-one day duration it was determined no degradation was observed.
It is recommended that further work be carried out at the laboratory-scale to explore the aerobic degradation step and render it successful. The feasibility of conducting the anaerobic process in-situ in man made ponds; land farms or biopiles should be investigated in future work.
