PREVENTION AND TREATMENT OF POLYCHLORINATED BIPHENYLS IN SEDIMENTS - SOURCES AND SOLUTIONS

Abstract

PCBs are classified as one of the persistent organic pollutants (POPs) with high toxicity and have undesirable effects on the environment and on humans. Once released into the environment PCBs could bioaccumulate within the food chain, due to their high affinity for organic materials. Recently, studies indicated PCBs can potentially enter a wastewater treatment plant (WWTP) system and be discharged via wastewater effluents thereby further contaminating the downstream environments. This study evaluated the potential for bioremediation of polychlorinated biphenyls (PCBs) in the effluent from a large WWTP. It was found that the continuous effluent was responsible for the majority of the discharged PCB into the receiving river (1821 g for five years), while the intermittent discharge contributed 260 g over the five years. The average number of chlorine per biphenyl for the detected PCB congeners showed a 19% difference between the two types of effluent, which indicated a potential for organohalide respiration of PCBs during the continuous treatment. This was further supported by a high level of tri-, tetra- and penta- chlorinated congeners accounting for 75% of the anaerobically respired PCBs. Potential for aerobic degradation and thus biomineralization of PCBs were identified for both effluents. In addition, the similarity of organohalide respiring (OHR) microbial populations in biosolids and intestinal human biofilms was determined by applying a bioinformatics approach. The OHR populations of the communities were analyzed from existing American and Chinese human intestinal microbiomes. The results of the biosolids analysis showed increased amounts of products from PCB respiration. Simultaneously, experiments with organohalide respiration of PCE in biosolids samples showed significant decreases in PCE concentration after 46 days (28-92%). Subsequently, it was evaluated if the OHR microbial populations in biosolids were similar to those present in intestinal human biofilms by applying a bioinformatic approach. The OHR populations of the communities were analyzed from existing American and Chinese human intestinal microbiomes. The overall groups Proteobacteria, Bacteroides, Actinobacteria, and Firmicutes phyla dominated the microbiomes in all datasets. The OHR groups in biosolids and intestinal biofilms included Dehalogenimonas, Dehalobacter, Desulfitibacter, Desulfovibrio, Sulfurospirillum, Clostridium, and Comamonas. The results of this study showed that several OHR phyla were present in all samples independent of origin. Wastewater and intestinal microbiomes also contained OHR phyla. Finally, biofilms made up by the OHR bacteria Dehalobium chlorocoercia DF-1 were inoculated on the surface of the pinewood biochar particles. The mole percent of the total PCE in the headspace decreased from 100% to 70.4%±17.6% for the rest of nine mesocosms which suggested that the D. chlorocoercia DF-1 biofilm converted PCE to TCE. The gene copy numbers of DF-1 biofilm from nine mesocosms which are ranging from 1.95×108 to 8.30×108 gene copies/g pinewood biochar. The biochar-biofilms were subsequently applied to PCB contaminated sediment from the Grass River in Michigan, USA. The goal was to evaluate the organohalide respiration of the PCB contaminated sediments in the absence/presence of the biofilm and free-floating inoculum.