The objective of this project is to apply a biofilm based delivery system to wea­the­­red polychlorinated biphenyl (PCB) contaminated sediments with low in situ PCB concentrations in order to promote enhanced dechlorination activity and subsequently complete PCB mineralization. The overall hypothesis is that the rate and extent of PCB dechlorination in aquatic sediments can be enhanced by the presence of active mi­cro­bial biofilms associated with sorptive surfaces, while the PCBs simultaneously are sequestered at the sorptive surface being unavailable for benthic organisms. The activity of the biofilm based system will benefit from active PCB dechlorinating bacteria grown to a high density, while located at the surface of the sequestering activated carbon or other sorptive surfaces.

The project will be conducted in two phases. In Phase I, the proof of principle for the biofilm based delivery system was shown using laboratory mesocosms containing high concentrations of Aroclor 1248 that were inoculated with biofilm covered activated carbon particles. Biofilms of anaerobic Dehalobium chlorocoercia DF1 and anaerobic enrichments from wastewater were formed on the sorptive surfaces and the mature biofilms were inoculated into PCB contaminated sediment mesocosms, where total PCB and individual congener concentrations were determined. Molecular techniques including DNA extraction, quantitative PCR with specific 16S rDNA primers for dechlorinating bacteria, identification by DHPLC, and sequencing were applied. Also, several microscopic analyses were developed to qualitatively and quantitatively analyze the PCB dechlorinating biofilms such as the fluorescent stain DAPI (4',6-diamidino-2-phenylindole), Peptide Nucleic Acid-Fluorescence In Situ Hybridization (PNA-FISH), Scanning Electron Microscopy (SEM), and Confocal Laser Scanning Microscopy (CLSM).

In Phase II, the fundamental processes responsible for the enhanced dechlorination in the presence of biofilm covered sorptive particles including activated carbon will be elucidated. Sorptive surfaces with different characteristics will be used for biofilm formation and analyzed for PCB degradation activity as well as DNA and RNA based transformations occurring in the biofilms. Also, methods for effectively scaling up the pro­duction of high quality and reproducible biofilm inoculum will be established. The biofilm delivery system will be tested in sediment mesocosms under relevant environmental conditions together with the activity, overall effect­i­ve­ness, cost, quality, and longer term sustainability of the biofilm inoculum in order to overcome the recalcitrance of weathered, low concen­trations of PCBs in sediments and thereby enhance PCB degradation.

Biofilm formation of Dehalobium chlorocoercia DF1 and anaerobic enrichments from wastewater was observed via multiple fluorescence staining and microscopic techniques. When the biofilms were inoculated into sediment mesocosms with high concentrations of Aroclor 1248, the bacterial numbers increased 2-fold and PCB dechlorination was enhanced by 31% for biofilms (1.5 chlorines/biphenyl) vs. 6% (0.3 chlorines/biphenyl for planktonic inoculum) over 200 days. The compositions of the bacterial populations were not influenced, thus not causing the difference in dechlorination. The enhanced PCB dechlorination might have been due to PCB adsorption onto the activated carbon particles ensuring direct contact between the PCB dechlorinating biofilms and the adsorbed PCBs. In summary, the proof-of-concept biofilm based two-phased delivery system can provide an efficient and cost-effective method for delivering microorganisms for bioaugmentation of PCB contaminated sites, thus enabling complete onsite bioremediation. The results of this study can be found in the Phase I Final Report.

Many Department of Defense facilities face challenges from contaminated aquatic sediments including PCBs, and the existing remediation options are slow and expensive. Bioremediation utilizing biofilms as the delivery vehicle is novel and can provide enhanced activity in PCB contaminated areas such as wetlands and under piers, where other remediation solutions will be ineffective. The results from this project will assist in the development of the next generation of contaminated sediment management tools, resulting in more efficient reduction of risk at lower costs and also more environmentally sustainable solutions. (Anticipated Phase II Completion - 2023)

Ming-ch'eng Adams C.I., J.E. Baker, and B. Kjellerup. 2016. Toxicological Effects of Polychlorinated Biphenyls (PCBs) on Freshwater Turtles in the United States. Chemosphere, 154:148-154. 

Demirtepe H., B. Kjellerup, K.R. Sowers, and I. Imamoglu. 2015. Evaluation of PCB Dechlorination Pathways in Anaerobic Sediment Microcosms using an Anaerobic Dechlorination Model. Journal of Hazardous Materials, 296:120-127.

Horwat M., M. Tice, and B. Kjellerup. 2015. Biofilms at Work: Bio-, phyto-and rhizoremediation Approaches for Soils Contaminated with Polychlorinated Biphenyls. AIMS Bioengineering, 4:324-334. 

Kjellerup B., C. Naff, S.J. Edwards, U. Ghosh, J.E. Baker, and K.R. Sowers. 2014. Effects of Activated Carbon on Reductive Dechlorination of PCBs by Organohalide Respiring Bacteria Indigenous to Sediments. Water Resources, 52:1-10. 

Lombard N.J., U. Ghosh, B. Kjellerup, and K.R. Sowers. 2014. Kinetics and Threshold Level of 2,3,4,5-tetrachlorobiphenyl Dechlorination by an Organohalide Respiring Bacterium. Environmental Science and Technology, 48(8):4353-60.