天然有机质和铁氧化物协同促进生物还原固定六价铬机理和应用研究

Chromium contamination in groundwater is a universal environmental problem in the world. The main strategy for in-situ remediation is to reduce dissolved Cr(VI) to insoluble Cr(III) precipitation using biotic/abiotic methods. However, the direct bioreduction of Cr(VI) is a slow process, several orders of magnitude slower than the abiotic reduction by Fe(II). The bioreduction of Fe(III) minerals by microorganisms is usually inhibited by Cr(VI). In our previous study, electron shuttles was found to help overcome the inhibition of Fe(III) minerals-mediated Cr(VI) reduction, suggestion a potential synergistic enhancement of electron shuttle and iron oxide on bioreduction of Cr(VI). Biotic and abiotic methods were coupled by adding electron shuttles. Base on this result, we will study the conditions of synergy effect in presence of natural organic matters (NOM) and iron oxides, and analyze the transformation of mass, energy and electrons. The relationship of kinetic and thermodynamic constants will be investigated. We will also characterize the products of Cr(VI)/iron oxides reduction, and gain insight into the mechanism of synergy effect in presence of NOM and iron oxides. Meanwhile, we will establish the in-situ synergistic process by simulating the conditions of the polluted sites. This project will provide technical assistance to develop new approach for Cr(VI) immobilization in groundwater. The effect between NOM and iron oxides that was reported in this study may have important implications for Cr(VI) migration and transformation in anaerobic environment.

地下水中Cr污染一直是全球范围内关注的环境问题。目前主要采用生物和化学方法在原位将溶解态Cr(VI)还原为Cr(III)沉淀修复。生物法还原过程缓慢，化学法利用Fe(II)还原Cr(VI)速率很快，但Fe(II)不能再生，使反应无法持续进行。申请人前期研究发现天然有机质的模型化合物电子传递体与铁氧化物共存时可协同促进Cr(VI)还原固定，实现生物与化学还原过程耦合，但机理未知。本项目拟研究天然有机质与铁氧化物协同促进生物还原固定Cr(VI)过程的机理，阐明该过程中物质、能量转化及电子传递途径，建立动力学与热力学的关系，明确协同作用下的热力学机制。结合界面表征手段，分析还原产物的形态及结构变化，揭示协同作用发生机理。通过模拟实验构建协同促进生物还原去除地下水中Cr(VI)的工艺。本项目将为Cr污染地下水修复提供新思路，并为研究富含天然有机质和铁氧化物的地下水环境中Cr迁移转化过程奠定基础。

铬盐被广泛应用于制革、冶金、电镀和印染等行业，对地下水环境造成严重的污染。利用耐铬微生物将的Cr(VI)还原为毒性低、迁移性差的Cr(III)是铬污染场地原位修复的有效方法。但Cr(VI)对微生物也有较强的毒性作用，且生物还原过程速率较慢，因此需构建适宜的强化工艺。针对该问题，本项目首先对铁矿物与电子传递体协同促进生物还原Cr(VI)的过程进行机理分析，确定协同作用发生条件；然后考察不同电子传递体与铁矿物组合条件下强化过程中动力学和热力学机制，构建动力学过程与热力学控制间的关系；最后结合实际污染场地，进行耐铬微生物分离筛选，并对其还原过程进行持续强化工艺构建。针对富含铁矿物的污染场地，本研究提供了一种利用电子传递体协同强化修复过程的方法，从而极大提高Cr(VI)污染场地生物修复的效率。