Biochar-based composite microspheres embedded with zero-valent iron and soybean oil efficiently remove 1,1,1-trichloroethane and reshape microbial community in simulated groundwater.

The increasing contamination of global groundwater by organic chlorine solvents poses a major threat to environmental and human health; however, there is a lack of structurally stable and effective materials for removing organic chlorine pollutants. In this study, biochar-based composite microspheres embedded with zero-valent iron (ZVI) and soybean oil were prepared and their effects on 1,1,1-trichloroethane (1,1,1-TCA) removal and the microbial community in simulated groundwater system were investigated. The composite microspheres achieved a remarkable 85.79% removal rate of 1,1,1-TCA after 360 h in groundwater, which was 1.63 times higher than that of ZVI + biochar microspheres (52.69%) and 1.33 times higher than that of soybean oil + biochar microspheres (64.50%). The composite microspheres also significantly reduced the oxidation-reduction potential to - 248.52 mV and maintained a neutral pH range of 6.8-7.2, thereby creating favorable conditions for long-term reductive dechlorination. The surface morphology of the composite was stable during degradation, reflecting its potential for long-term usage. The rich network structure of microspheres and the micropore structure of the biochar were conducive to the capturing of pollutants, safety of microorganisms, and slow release of organic carbon. 16S rDNA sequencing demonstrated that the composite significantly affected the diversity and stability of the microbial community, especially promoting the growth and interaction of dechlorinating and fermentative microorganisms in the groundwater and composite microspheres. The preliminary removal mechanisms included biochar-induced adsorption and ZVI-induced chemical reduction in the early stage and biochemical coupling of dechlorination in the middle and last stages. The biochar-based composite microspheres significantly enhanced the effectiveness and consistency of 1,1,1-TCA removal, potentially being applied to in situ enhanced reductive dechlorination of organochlorine solvents in site groundwater. Moreover, considering the abundant porous structure and easy availability of biochar, it can effectively promote the sustainability and cost-efficiency of the microspheres during application.