生物炭基零价铁加速非生物与生物过程修复铬污染土壤的协同作用机制研究

Biochar-based Fe0 (Bc-Fe0) soil remediation process has the functions of in-situ, low cost and keeping favorable agricultural function. This method may be a good prescription for the remediation of large area farm land fields which are contaminated by medium or low density of chromium in south China. The object of this research is to reduce high toxic and carcinogenic Cr(Ⅵ) to low toxic Cr(Ⅲ) in soil. Two basic problems are emphasized before the large scale application of Bc-Fe0 in this project: (1) Cr(Ⅵ) removal efficiency of Bc-Fe0 obtained from different biomass and synthesis conditions; (2) synergistic mechanism for the remediation of chromium by abiotic and biotic processes and the feasibility to reduce chromium enrichment in crops. We will employ a roasting reduction process to prepare various porous Bc-Fe0 particles and select an effective Bc-Fe0 based on its capacity for Cr(Ⅵ) removal. The positive ecological effect of the selected Bc-Fe0 for indigenous microorganisms will be analyzed with the change of hydrogen-consuming bacteria and iron-oxidizing bacteria during the remediation process. The capacity of the selected Bc-Fe0 and the microorganisms for the adsorption, reduction and passivation of Cr(Ⅵ) in soil will be studied, and the synergistic mechanism for the remediation of chromium by abiotic and biotic processes as well. The reduction of bioavailability of chromium from soil to typical vegetable such as water spinach will be studied. Moreover, the remediation efficiency and application conditions of this remediation system also will be evaluated and optimized. This study can provide basic theory and technical support for in-situ remediation of chromium-contaminated soil and the restoration of its agricultural function.

以生物炭基Fe0(简称炭基Fe0)为基础的土壤修复技术具有原位、廉价和不丧失农用功能的特征，可能是修复我国南方污染程度中等偏低但面积大的农田土壤的良方。本项目以高毒致癌性的Cr(Ⅵ)还原成毒性较低的Cr(Ⅲ)为修复目标，侧重研究炭基Fe0规模化应用之前尚存的两大基础问题：(1)研究由不同生物质和不同条件制作的炭基Fe0对Cr(Ⅵ)处理的有效性；(2)研究炭基Fe0钝化Cr(Ⅵ)的化学与生物协同机制及降低铬在作物中富集的可行性。我们将采用还原焙烧法制备出各种多孔性炭基Fe0并筛选出高效品种。研究所筛选炭基Fe0对土著微生物生态促进作用(侧重鉴别嗜氢菌和铁氧化菌类型和丰度随时间变化)及其与微生物吸附、还原和钝化土壤中Cr(Ⅵ)的效能及化学与生物协同作用机制；对降低铬从土壤中向典型蔬菜如蕹菜富集的生物有效性；评估修复效果并优化应用条件，为铬污染土壤原位修复并恢复其农用功能提供理论依据与技术支持。

以零价铁材料为基础的土壤修复技术具有原位、廉价和不丧失农用功能的特征，可能是修复铬污染程度中等偏低但面积大的农田土壤的良方。本项目以高毒致癌性Cr(VI)还原成为毒性较低的Cr(III)并降低其从土壤向典型蔬菜如蕹菜富集为修复目标，考察了羧甲基纤维素改性纳米零价铁、生物炭基零价铁和零价铁与微生物协同固定Cr(VI)的过程。结果表明，羧甲基纤维素和生物炭基零价铁均可以提高零价铁的分散性和反应活性，而微生物则通过胞外聚合物诱导零价铁腐蚀释放的Fe2+生成纤铁矿、磁铁矿和绿锈等高活性矿物，大幅度提高零价铁吸附、还原和固定Cr(VI)的效果，使得土壤中水溶态、离子交换态和碳酸盐结合态Cr(VI)被还原成Cr(III)并生成Cr-Fe沉淀物固定到零价铁表面氧化铁矿物中，大幅度降低Cr的生物可利用性。与未修复体系相比，零价铁与微生物协同修复体系中蕹菜铬摄取量下降79%，比单独零价铁修复体系提高了2.6倍，表明微生物可提高零价铁修复铬污染土壤的效果，是一种高效的铬污土壤修复方法。