BIOREMEDIATION OF POLYCHLORINATED BIPHENYLS IN SEDIMENT USING BIOFILMS ON ACTIVATED CARBON

Removal of polychlorinated biphenyls (PCBs) from contaminated aquatic sediments is a priority because of their ability to enter the food chain and their toxic properties. Common remedies include dredging and capping which are associated with challenges such as disruption of existing habitat and high cost. While in situ microbial degradation of PCBs can represent a sig­nificant improvement, previous attempts have failed because of PCB stability, low bioavailability, and the low abundance and activity of indigenous PCB-degrading microorganisms. The high efficiency of activated carbon (AC) to quickly sequester PCBs from sedi­ments has been demonstrated. Co-localizing PCB-degrading microbes onto the surfaces of the sorp­tive particles as biofilms and utilizing them as a microbial inoculum delivery system pro­vi­des a novel approach to address PCB contamination. In this study, biofilm covered AC particles were applied for bioremediation enhancement of PCBs in sediments.

A novel delivery system utilizing AC as growth sur­face for biofilm formation by PCB-degrading bacteria was applied benefitting from bacterial growth to a high density at the surface of sequestering AC. Biofilms of anaerobic Dehalobium chlorocoercia DF1 and enrichments from wastewater were formed and mixed into PCB contaminated sediment mesocosms. Total PCB and individual congener concentrations were determined by GC. Molecular techniques included: DNA extraction, q-PCR (16S rDNA primers), identification by DHPLC, Illumina sequencing and fluorescence microscopy.

Biofilm formation on AC was observed via microscopy. Biofilm inoculation increased PCB dechlorination by 31% vs 6% for liquid bacteria, while the numbers of DF1 increased two fold over 200 days. Metagenomic analysis showed that additional 15 bacterial groups were 2-35 fold upregulated in the presence of biofilm. All groups were related to anaerobic transformation of organic contaminants showing a wider effect than PCBs.

The application of biofilm covered AC particles enhanced PCB dechlorination in sediment. This was likely due to PCB adsorption onto AC ensuring direct contact between the biofilms and PCBs thus enhancing electron transfer. This two-phased approach will provide an efficient and cost-effective delivery method thus enabling complete onsite bioremediation.