Degradation of polybrominated diphenyl ethers by a sequential treatment with nanoscale zero valent iron and aerobic biodegradation

BACKGROUND: Polybrominated diphenyl ethers (PBDEs) are emerging persistent organic pollutants. Degradation of PBDEs is a significant challenge owing to their extreme persistence and recalcitrance nature. The objective of this study was to evaluate the effect of a sequential nano-bio treatment using nanoscale zero-valent iron (nZVI) and diphenyl ether degrading bacteria Sphingomonas sp. PH-07 for degradation of PBDEs. RESULTS: In the bacterial tolerance test for determining the maximum endurable concentration of nZVI, the PH-07 strain was able to grow in the presence of nZVI up to 5 g L ^-1 in minimal salt medium by using non-brominated diphenyl ether as growth substrate. Reductive debromination of decabrominated diphenyl ether (deca-BDE; 1 mg) with nZVI (100 mg per vial) resulted in a 67% reduction of deca-BDE and produced various intermediates ranging from nona-BDEs to tri-BDEs during a 20 day period. Additional experiments with 2,4,4′-tri-BDE and 2,4,6-tri-BDE as initial substrates revealed that both tri-BDEs were further debrominated to mono-BDEs. Following the reductive debromination process, reaction mixtures were aerobically treated with DE-grown Sphingomonas sp. PH-07 strain to mineralize the low brominated-DEs (tri-BDEs-mono-BDEs) for additional 4 days. During bacterial treatment, the low brominated-DEs were biologically degraded to bromophenols and other prospective metabolites. CONCLUSIONS: The nZVI-biological sequential treatment method was found to be effective for degradation of PBDEs through reductive debromination followed by biological oxidation. This hybrid treatment method may lead to the development of a remediation strategy for highly halogenated environmental pollutants in contaminated sites.