[Effects of Modified Biochar-Supported Zero-Valent Iron on the Removal of Trichloroethylene and Responses of Microbial Community in Soil]

Trichloroethylene is a typical organic contaminant that has widely existed in industry sites and groundwater. Biochar-supported zero-valent iron material has been used to remove trichloroethylene in groundwater; however, it could affect the microbial communities in aquifer soil, leading to changes in the environmental behavior of trichloroethylene. In this study, biochar was prepared under oxygen-limited conditions and modified by NaOH and HNO₃ agents. Then, a modified biochar-supported zero-valent iron composite (BC composites) was synthesized using ball milling technology. The effects of BC composites on the removal of trichloroethylene and the responses of the microbial community were investigated under the condition of simulated aquifer soil. The results showed that the specific surface areas of BC composites were increased after the modification with NaOH. The highest removal rate of trichloroethylene was observed in the BC_2 treatment, up to 90.01%. Except in the BC_1 treatment, the diversity and abundance of soil microorganisms were increased, and the microbial community structure was changed after the addition of different BC composites, in which Bacillus, Thiobacillus, and Pseudomonas might have been the potential degrading bacteria of trichloroethylene. The abundance of Thiobacillus and Pseudomonas increased under the BC_2 treatment, which was favorable to the removal of trichloroethylene. The stabilization of the microbial community structure was probably maintained by Nocardioideas, Thermincola, Lysobacter, Gemmatimonas, Microvirga, and Pseudomonas. According to the predictive analysis of microbial metabolic pathways, the abundance of xenobiotics biodegradation and metabolism genes and the folding, sorting, and degradation of genes were the highest under the BC_2 treatment. Thus, the NaOH-modified BC composite could prompt the removal of trichloroethylene in simulated aquifer soil, probably due to the increase in the abundance of soil-degrading bacteria and the expression of degradation genes, demonstrating that the NaOH-modified BC composite could be used for the remediation of the organic-contaminated industry sites as a new composite material.