[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.

[Impacts of Biochar Input on Mineralization of Native Soil Organic Carbon].

Since the biochar was applied in soil, its function in carbon sink had become a research hotspot recently. However, the present studies showed that its function in carbon sink remained controversial and the interaction between biochar and soil organic carbon remained to be investigated. So our study used paddy soil (C3 soil) as the experimental soil, and added washed (CS) or unwashed (CN) corn stalk (C4 crop). Biochar was mixed with soil uniformity by two kinds of weight, each treatment was 1% and 3% of the soil (CS1%, CS3% and CN1%, CN3%). Soil without biochar was used as the control treatment (CK), every treatments repeated three times. Then indoor culturing experiments was carried out to study the effect of biochar on the mineralization of organic carbon. The results showed as follows: (1) During the 180 days' experiment, the accumulated amount of released CO2 in CS1%, CS3% and CN1% groups were 1865.7, 1864.4 and 1856.2 mL x kg(-1) respectively, all were higher than the CK (1779.0 mL x kg(-1)). But the differences were not significant. However, the accumulated amount of released CO2 in the CN3% group was the highest (2289.1 mL x kg(-1)), which was significantly higher than those of all other groups. This showed that high addition of CS biochar significantly reduced the soil CO2 release. (2) The accumulated amount of released CO2 of native soil from the CK treatment, CS treatment and CN treatment were 1534.2, 1000.4 and 1153.7 mL x kg(-1) respectively, among which the CK group is significantly higher than the others. It showed that additions of two kinds of biochar both could inhibit the mineralization of organic carbon in the soil. The result of priming effect also proved that: the PE value of CS 3% group was -34.8%, and the PE value of CN 3% group was -24.8%. This showed that the negative priming effect significantly induced by washed (CS) biochar.