Emulsion-enhanced recovery and biodegradation of decabrominated diphenyl ether in river sediments.

Purpose: Polybrominated diphenyl ethers (PBDEs) are flame retardants and regarded as emerging contaminants and persistent organic pollutants (POPs). Due to high lipophilicity and low biodegradability, they tend to accumulate in sediments. Decabrominated diphenyl ether (BDE-209) is the most predominant congener among 209 PBDE congeners in river sediments, accounting for more than 90 % of total PBDEs in most samples. This study is to explore the feasibility of an integrated remedial approach, direct removal by emulsion recovery and subsequent biological reductive debromination. Materials and methods: A double emulsion (water in oil in water) was formulated and used in direct recovery of BDE-209 in sediment samples. After this recovery operation, the residual oil left in sediments was used as an electron donor for anaerobic microbial reductive debromination. In order to improve the robustness of this direct recovery method, a variety of operational parameters and environmental variables were tested, such as mixing speed, mixing time, initial concentrations of BDE-209, salinity contents of sediment, and fractions of humic acids. A biodegradation experiment with different humic acid contents and with or without residual emulsion was conducted to compare the biodegradation rates under different conditions. All samples were extracted by using accelerated solvent extraction and detected by a gas chromatography with an electron capture detector. Results and discussion: In this study, we used an emulsion to recover BDE-209 in simulated sediment samples with different salinity and humic acid contents. BDE-209 was recovered as much as 96.10 % in a single recovery operation under a condition similar to the real situation of Er-Ren River in Taiwan. The biodegradation of unrecovered BDE-209 was assessed under anaerobic conditions with residual emulsion as an electron donor. The average half-life is 11.7 ± 1.9 days with residual emulsion, which is about 40 % shorter than that of those without emulsion and much shorter than those reported in literature. Real sediment samples were also tested and the result indicated that this method is highly feasible. Conclusions: Emulsion-enhanced recovery and biodegradation could be a highly feasible way to remove BDE-209 in river sediments. This method is not sensitive to the initial concentration of BDE-209 but sensitive to the salinity and humic acid concentration in sediments. [ABSTRACT FROM AUTHOR]