生物硫化-纳米零价铁体系修复地下水镉污染的反应机制研究

Nanoscale zero valent iron (nZVI) as one of green nanomaterials has been widely applied in organic polluted groundwater remediation. However, no application of nZVI in heavy metal polluted groundwater remediation has been reported so far. One reason is that the compounds (nZVI-Me) formed by nZVI and metal ion usually present weak stability and could be easily decomposed. This will lead to unwilling metal ion re-release problem. Sulfate reduction bacteria (SRB) is one of pervasive bacteria in groundwater, which possess potential leading to nZVI sulfidation, thus may enhance metal ion removal efficiency and the stability of nZVI-Me. In this research, basing on our previous study, we systematically investigated the interactions between nanomaterials and SRB, and carefully studied the underlying mechanism. Besides the influences of nanomaterials on SRB growth and spatial distribution, effects of SRB on nanomaterials transportation and transformation were also investigated. Influences of nitrate and dissolved oxygen in groundwater on Cd removal performance in nZVI-SRB remediation system were also carefully studied to reveal its interacting mechanism. Expected achievements from this project will not only provide feasible techniques for heavy metal remediation by nZVI-SRB system, but lay a solid theoretical foundation for this technique as well.

纳米零价铁作为绿色纳米材料已被广泛用于地下水有机污染污染修复，但其在地下水重金属污染领域的应用却迟迟未见报导，其原因之一在于纳米零价铁组分及结构衍化可能导致金属离子的二次释放。地下水中普遍存在的硫酸盐还原菌（SRB）具有将纳米零价铁及其氧化产物硫化的潜力，存在提高其对金属离子去除的能力和增强纳米零价铁与金属离子结合物化学稳定性的可能。本研究在前期研究的基础上，对生物硫化作用是否能加强纳米零价铁修复地下水镉污染处理能力及处理效果进行全面研究，深入探讨不同老化阶段纳米零价铁在地下水镉污染修复过程中与SRB之间相互关系及其作用机理，包括纳米材料对SRB的生长分布及SRB对纳米材料迁移转化的影响等问题，阐明地下水中普遍存在的硝酸根及溶解氧对纳米零价铁-SRB修复体系的影响机制。预期成果将为纳米零价铁修复地下水重金属污染提供理论与实践支撑。

本研究重点探索了纳米零价铁（nZVI）主导的结合硫酸盐还原菌的地下水重金属污染修复效果评估，详细探讨了nZVI在地下水中的结构和化学组分衍化，研究了化学及生物硫化对纳米零价铁理化性质及的影响，探明了nZVI及其衍化后产物与重金属（Cd、Cr）和地下水中功能微生物间的相互作用（地杆菌Geobacter 和硫酸盐还原菌SRB），详细阐述了SRB的引入如何避免金属离子的二次释放。研究发现硫化增强了nZVI的化学稳定性、反应活性以及在地下水中的迁移能力，nZVI引入创造的厌氧环境以及活性氢能促进功能微生物的生长，其快速吸附重金属的能力降低了重金属对功能微生物的毒害作用，进而大大强化了功能微生物对重金属的去除效果。同时，功能微生物也能增强nZVI修复地下水重金属污染的能力，能显著增强SRB-nZVI-重金属复合物的化学稳定性。成果为纳米零价铁复合功能微生物修复地下水重金属污染提供了坚实的理论与技术支撑。