修饰型纳米零价铁修复重金属污染河道底泥的行为机理与微生物群落响应研究

The heavy metal in river sediment is a major threat to ecological environment and human health, which is one of the most urgent problems. It was confirmed that modified nanoscale zero-valent iron (nZVI) could be used to remediate heavy metal polluted sediment. However, the related mechanisms are unclear. Therefore, we will study the behaviour mechanisms and the microbial community response during the remediation of heavy metal polluted sediment by modified nZVI. Main research contents include: Preparation, optimization and characterization of modified nZVI will be studied. The process optimization and the behaviour mechanisms during the remediation of heavy metals polluted sediment by modified nZVI will be investigated. To reveal the remediation effects, we will also discuss the transport and bioavailability of heavy metal in remediation of polluted sediment by modified nZVI. The responses of microbial community structure, gene diversity and metabolic ability to modified nZVI will be emphasized. As a result, the process mechanisms in the remediation of river sediment by modified nZVI will be understood scientifically in terms of 2 aspects (remediation behaviour and microbial community response). The study could provide a theoretical supports for the remediation of heavy metal polluted sediment by modified nZVI, which benefit to the polluted sediment remediation and the ecosystem improvement.

河道底泥重金属污染威胁着生态环境及人类健康，是亟待解决的问题。目前已证实修饰型纳米零价铁（nZVI）能经济有效地修复重金属污染底泥，但有关机理尚不清楚。为此，本项目拟以湖南省湘江长沙段重金属污染底泥为对象，研究修饰型nZVI修复重金属污染河道底泥的行为机理与微生物群落响应机制，包括：优化制备修饰型nZVI及进行性能表征，深入研究修饰型nZVI修复污染底泥的过程优化及行为机理；探讨修复底泥中重金属的迁移转化特性与生物有效性变化；剖析修复过程底泥微生物群落结构、基因多样性与代谢功能等响应机制，从微观分子水平揭示修复效应。最终从修复行为机理、微生物群落响应机制两个方面科学认识修饰型nZVI修复重金属污染河道底泥的过程机理。本研究可为发展修饰型nZVI修复重金属污染河道底泥技术提供理论支撑和方法参考，利于实现有效处理底泥重金属与改善河道生态环境。

高效修复重金属污染底泥的新技术方法与理论是水环境领域一直关注的重要问题。本项目从修饰型nZVI修复污染底泥的过程优化及行为机理、修复底泥中重金属的迁移转化特性与生物有效性、底泥微生物群落结构与基因多样性响应机制等三个方面，对实现修饰型nZVI修复重金属污染河道底泥与改善河道生态环境有重要意义。主要结论：（1）优化研发了修饰型纳米零价铁的制备新方法，通过多方面表征分析发现用十二烷基硫酸钠、鼠李糖脂、海藻酸钠、羧甲基纤维素钠制得的SDS-nZVI、RL-nZVI、SA-nZVI、C-nZVI的性能好，深入揭示了不同修饰型nZVI对底泥重金属的修复作用机理。SDS-nZVI将Cr(VI)还原为Cr(III)，与零价铁生成的Fe2+生成铁铬络合物于纳米铁表面；SA-nZVI依赖活性官能团羟基，RL-nZVI依赖羟基和羧基，与重金属形成螯合物，两者对重金属的吸附均符合准一级动力学模型；各种修饰型nZVI表面及表面生成的铁氧化合物、氢氧化合物可吸附重金属Pb、Cd等。（2）发现各种修饰型nZVI均显著降低了底泥重金属生物有效性和毒性，RL-nZVI将可迁移态Cd和Pb转化为稳定的形态(残渣态)，主要包括非生物作用（即与nZVI的反应）与生物作用；C-nZVI可使酸溶态镉转化为较稳定的络合产物FeOCdOH，铁氢氧化物络合作用生成的络合产物FeOCd+或FeOCdOH能有效抵抗中、强酸的提取；修饰型nZVI修复后使底泥pH值升高，也是其使重金属钝化的机理之一；对Cd除了吸附、络合作用外，还通过激发Fe(III)还原菌的生长和还原铁矿物质而将铁氧化物结合态的Cd重新分配到更稳定的铁矿物相中，降低Cd迁移。（3）通过PCR-DGGE和高通量测序及生物酶活等分析发现，修饰型nZVI显著改变了底泥微生物群落结构，增加了底泥细菌群落的多样性和Fe(III)还原菌的丰富度，使脲酶和过氧化氢酶活性升高，提高了群落对有机碳的利用率。