Process and mechanism of 2,3-dichlorophenol reduction by microscale zero-valent iron-coupled Desulfitobacterium hafniense DCB-2

Chlorophenols (CPs) pose potential threat to the environment and public health due to their persistence and high toxicity. Zero-valent iron coupled with microorganisms have been applied for the degradation of halogenated organic matter, which is considered as a remediation technology of increasing interest. However, few studies have attempted to investigate the effects of this coupled system on CPs degradation and to comprehensively unveil the governing mechanisms. In this study, we systematically compared the effects of the composite system of microscale zero-valent iron (mZVI) with different particle sizes and Desulfitobacterium hafniense DCB-2 (i.e. 3 μm mZVI + DCB-2, 5 μm mZVI + DCB-2, and 10 μm mZVI + DCB-2) on the process of bioreductive dechlorination of 2,3-dichlorophenol (2,3-DCP). Interestingly, the lower particle sizes of mZVI (3 μm and 5 μm) were more favorable for rapid 2,3-DCP bio-dechlorination due to the fact that mZVI with smaller particle size were less likely to agglomerate with strain DCB-2, which facilitated the transfer of electrons from strain DCB-2 to 2,3-DCP. Besides, the optimal particle size of mZVI (3 μm) was selected from the above experimental results to further explore the percentage generation of reduction products and the dechlorination pathway of 2,3-DCP in composite system. The results showed that the low toxicity product 2-chlorophenol (2-CP) accounted for 31.76 % of the composite system, while in the pure bacteria treatment this value was only 20.42 %. The mZVI and DCB-2 coupling strategy might provide a new idea and feasible solution for the green reduction of chlorinated phenols.