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Sediment contamination in Taiwan is a critical environmental problem because it threatens human health through food chains and the local ecosystem as well. Er-Ren River (ERR) in southern Taiwan is one of the most polluted and its sediments have been severely contaminated by hydrophobic organic compounds (HOCs). Among all HOCs, polychlorinated biphenyls (PCBs) have been detected at high levels while hexachlorobenzene (HCB) has been most frequently detected. Due to their higher Kow values and lower biodegradability, they can be biomagnified through trophic levels and consequently pose high risks to humans and the ecosystem. This field study is to demonstrate an effective remediation technology on sediments contaminated by Aroclor 1254 and HCB by coupling in situ phase-inversion emulsification and biological reductive dechlorination (ISPIE/BiRD). By using real contaminated sediment with weathered and freshly-added contaminants, a single ISPIE operation can remove about 62% and 60% of weathered Aroclor 1254 and HCB, respectively. For weathered HCB and Aroclor 1254, the total removal could reach as high as 98% in 70 days. Metagenomic results showed that heat selection during ISPIE significantly changed the diversity and species evenness of the microbial community and that the Dehalococcoides were not positively correlated with the PCB removals. Instead, heat-tolerant archaea, Methanosaeta spp., may play much more important roles in the subsequent biological dechlorination. These results strongly support that ISPIE/BiRD is highly feasible on a full-scale field remediation and that this new microbial consortium could be a highly effective tool for bioremediation of HOC-contaminated sediments.

River sediment contamination is a critical environmental problem. Concentrations of certain hydrophobic organic compounds (HOCs) in sediments in Taiwan are ranked at the top in the world. In this study, we proposed a novel in situ phase-inversion emulsification and biological reductive dechlorination (ISPIE/BiRD) method that integrates (1) heating contaminated sediments by hot water-in-oil emulsion to increase the contact between hydrophobic organic contaminants (HOCs), to accelerate the mass transfer between two phases, and to select heat-tolerant hydrogen-producing bacteria, (2) ISPIE forming oil-in-water emulsion to enhance recovery of HOCs by pushing cool water and nutrient buffer through the sediment column, and (3) subsequent BiRD using residual emulsion in sediment. Aroclor 1254 and hexachlorobenzene (HCB) were selected due to significantly higher human health and ecological risks in sediments. Batch biological dechlorination tests were conducted using an L 9(34 ) orthogonal table according to the Taguchi method . The results showed that significant controlling factors for biological dechlorination were temperature and emulsion concentration. A single operation of ISPIE can achieve the removal of Aroclor 1254 and HCB at as high as 58.2% and 56.5%, respectively. Column study on BiRD further removed about 30% of the residual Aroclor 1254 and HCB at the upper and middle sections of the sediment cores in 35 days. These results supported that ISPIE/BiRD is feasible for HOC-contaminated sediments remediation.