Biodegradation of Polychlorinated Biphenyls in Two-Phase Partitioning Bioreactors
Started May 2003 at Queen’s University under the supervision of Dr. A.J. Daugulis
Poly-chlorinated biphenyls (PCBs) are exclusively man-made organochlorines, commercially available until the late 1970s under the product name Aroclor. They are banned due to their health risk to humans and to the environment [1]. PCBs are extremely hydrophobic, as well as chemically and biologically inert, which leads to their persistence once introduced to the environment. Biodegradation, however, occurs at a low rate in the environment by either anaerobic or aerobic microorganisms. Highly chlorinated PCBs can only be degraded sequentially by anaerobic and aerobic organisms [2]. Factors limiting PCB degradation in soil are physical conditions such as temperature and pH as well as nutritional requirements and the low bioavailability of PCBs, as they are sorbed to the soil matrix or dissolved in other organic contaminants such as mineral oil, which often co-contaminate PCB contaminated sites [3]. Engineered bioremediation can overcome these limitations and therefore provides conditions under which PCB degradation occurs at much higher rates than in the environment [4]. The process proposed in this study involves the extraction of PCBs from soil, followed by sequential anaerobe/aerobe treatment in two-phase partitioning bioreactors (TPPBs). The PCB extraction is provided by SAIC Canada and the biodegradation is the subject of this thesis. TPPBs are bioreactors consisting of an aqueous phase, enabling microbial growth, and an organic phase in which high concentration of highly hydrophobic substances, in this case PCBs, can be dissolved [5;6]. These substances are delivered into the aqueous phase based on the microbial consumption rate and thermodynamic equilibrium.
The key objectives of this research are:
to design an anaerobic process which utilizes a microbial consortium in a TPPB to dechlorinate highly chlorinated PCBs to a level of 40% w/w chlorine,
to design an aerobic process which utilizes pure cultures of specialized microorganisms to mineralize PCBs containing up to 40% w/w chlorine, and
to sequentially combine the above two processes to achieve complete mineralization of highly chlorinated PCBs.
This research will not only provide an unique process for PCB bioremediation, but also provide
insight and understanding into processes occurring at a PCB-contaminated site. While effects such as changes of bioavailability due to partitioning of PCBs between an organic and an aqueous phase are very difficult to study in contaminated soils [3], they can be easily studied in a controlled reactor environment.
References:
[1] Agency for Toxic Substances and Disease Registry (ATSDR). (2000) Toxicological profile for polychlorinated biphenyls (PCBs). Department of Health and Human Services, Public Health Service, Atlanta, GA: U.S.
[2] Abramowicz,D.A. (1990) Aerobic and Anaerobic biodegradation of PCBs: A Review. Critical Reviews in Biotechnoloy,10, 241-300.
[3] Cohen,R., Mercer,J., & Matthews,J. (1993) DNAPL Site Evaluation. C.K. Smoley. Robert S. Kerr Environmental Research Laboratory. U. S. EPA, EPA/600/R-93/022.
[4] Fava,F., Di Gioia,D., & Marchetti,L. (2000) Role of the reactor configuration in the biological detoxification of a dump site-polychlorobiphenyl-contaminated soil in lab-scale slurry phase conditions. Appl. Microbiol. Biotechnol., 53, 243-248.
[5] Daugulis,A.J. (1997) Partitioning bioreactors. Curr. Opin. Biotechnol., 8, 169-174.
[6] Daugulis,A.J. (2001) Two-phase partitioning bioreactors: a new technology platform for
destroying xenobiotics. Trends Biotechnol., 19, 457-462.
