Rapid reactivation of aged NZVI/GO by Shewanella CN32 for efficient removal of tetrabromobisphenol A and associated reaction mechanisms

Tetrabromobisphenol A (TBBPA) is one of the most widely applied brominated flame retardants, which has consequently resulted in severe environmental contamination. Graphene oxide-loaded nanoscale zero-valent iron (NZVI/GO) has previously shown excellent performance for potential TBBPA removal. However, the aging of NZVI/GO resulted in reduced reaction rates. In this study, Shewanella CN32 was used to reactivate the performance of aged NZVI/GO. The results demonstrated that CN32 significantly reactivated aged NZVI/GO (27%) and consequently improved the removal of TBBPA by 240% in aged NZVI/GO+CN32 (92%). Compared to aged NZVI (0.07 mM), CN32 rapidly decomposed the iron oxide passivation layer of aged NZVI/GO, with a subsequent increase in the release of Fe2+ ions (0.12 mM). Moreover, Fe(II) vivianite (Fe-3(II)(PO4)(2)center dot 8H(2)O) and SO42- type green rust (Fe3.6Fe0.9(O,OH,SO4)(9)) formed at the surface of aged NZVI/GO+CN32-. GO accelerated the reduction of dissimilatory iron (alpha-Fe2O3) and the formation of vivianite crystals. Vivianite further improved the debromination of TBBPA. Furthermore, the semiquinone radicals (C=O) in the interface of the aged NZVI/GO effectively mediated electron transfer and reactivated the performance of aged NZVI/GO by CN32. It could therefore be concluded that CN32-induced iron oxide reduction and NZVI exposure, C=O mediated electron transfer, and vivianite-induced debromination were the main removal mechanisms of TBBPA in the system. It is a potential technology for convenient remediation of soil, groundwater, and lake.

Automated summary

This study showed that Shewanella CN32 effectively reactivated aged NZVI/GO, improving the removal of TBBPA. The main removal mechanisms involved iron oxide reduction, electron transfer, and debromination induced by vivianite. This technology has potential for convenient remediation of soil, groundwater, and lake.