Reductive dechlorination of 1,1,2-trichloroethane in groundwater by zero valent iron coupled with biostimulation...

Zero-valent iron (ZVI) coupled with biostimulation is recognized as one of the most promising and effective dechlorination methods for chlorinated hydrocarbons in groundwater. However, the heterogeneity of the aquifer environment may affect the dechlorination efficiency of the coupled systems, and the underlying mechanisms remain unclear. In this study, we systematically explored the effect and potential mechanism of sulfate (SO₄^2-) on the removal of 1,1,2-trichloroethane (1,1,2-TCA) by the coupled ZVI and biostimulation. Results revealed that the coupled systems enhanced the degradation rate of 1,1,2-TCA by an order of magnitude compared with that of each individual treatment under SO₄^2- stress. However, the complete dechlorination of the main product, vinyl chloride (VC), remains challenging in the absence of obligate organohalide respiration bacteria (OHRB). SO₄^2- dynamically altered the sulfidation degree of ZVI and microbial interactions, leading to the disappearance of non-chlorinated products in the micron ZVI (mZVI) coupled system and decreased dechlorination efficiency with increasing SO₄^2- concentration. In the nano ZVI (nZVI) coupled system, suitable SO₄^2- concentrations promoted continuous VC degradation, likely due to the inherent high reactivity of the nanometer-size effect. Nevertheless, excessive SO₄^2- reduced ZVI sulfidation, causing differences in dechlorination efficiency and extent trends between mZVI and nZVI coupled systems. These findings will provide scientific support for the optimal application scenarios and limitations of the coupled strategies, thereby facilitating the regulation of technology application according to actual aquifer environmental parameters to achieve low-cost environmental safety control.