微生物燃料电池对水稻土中铁、砷行为的调控机制研究

Arsenic (As) pollution in paddy fields has received enormous attention because rice is the major source of As exposure in China. Paddy fields are intermittently flooded during rice cultivation, during which times iron (Fe) oxides are reduced by iron reducing bacteria. In consequence，the As adsorbed onto these Fe oxides will be released into water where it is utilized by living organisms, like rice. Thus, the redox cycling of Fe oxides is vital for the As mobilization..Microbial fuel cells (MFCs) are an emerging technology wherein the extracellular respiration of bacteria is exploited to convert the chemical energy stored in the organic matter in environmental media to electricity. The application of MFCs has extended to wastewater treatment, seawater purification and detoxification of heavy metals. Our preliminary research has shown that the deployment of MFCs in As-contaminated paddy soils could slow down the reduction of iron oxides when the soils are flooded, thereby reducing the As levels in pore water and rice plants resulting from Fe oxide dissolution. In this project, we will elucidate the mechanisms that modulate iron redox cycling and arsenic mobilization by using state-of-the-art techniques..During the project, we will first investigate the interactions between the MFC anode and iron oxides in a two-chamber MFC without soil involvement. Metal speciation in this well control system will be routinely monitored via electrochemical and other methods of analysis (e.g. Inductively Coupled Plasma – Mass Spectrum). The same experiments will be conducted with soils present, during which the chemical profile and microbial community change along the interface between the MFC electrodes and bulk soils will additionally be studied with the diffusive gradient in thin films technique and high-throughput DNA sequencing, respectively. .The project will significantly contribute to the development of remediation methods for agricultural fields that are contaminated with As and enhance our understanding of the microorganism-mediated coupling of Fe and As behavior in rice paddy soils.

水稻土中铁循环是控制砷的生物有效性的关键。微生物燃料电池作为新兴的环境友好技术，具有调控微环境氧化还原过程和离子迁移的能力。本研究组的研究结果表明，微生物燃料电池与水稻土的结合，可改变土壤中铁矿物的溶出速率，进而改变砷的生物有效性。然而，微生物燃料电池电极对土壤铁矿物的作用机理及水稻土中砷行为的调控机制尚不清晰。因此，本项目拟采用简单溶液体系和实际土壤体系，结合电化学控制方法、电感耦合等离子质谱和梯度扩散薄膜技术，分析电极干涉下控制铁矿物还原过程的关键环境因子，并考察电极对铁砷等元素形态变化动力学及空间分布的影响；借助高通量测序方法，探究在该体系中胞外呼吸微生物的作用。从而揭示稻田土中植入微生物电池后电极通过化学与（或）生物作用，调控土壤铁矿物及砷释放的机理。本课题将深入理解稻田土壤中氧化还原过程及其相关的元素形态变化过程，并为稻田砷污染控制提供理论和技术指导。

农田污染以及水稻淹水栽培极易引起有毒重元素在水稻籽粒中的富集，造成稻米重金属元素超标，危害人类健康。因此，抑制水稻籽粒中有毒重金属元素富集刻不容缓。本项目针对稻田土壤砷污染问题，提出一种新型的修复策略，即采用微生物燃料电池技术，持续地控制土壤孔隙水的铁和砷的释放，进而减少砷从土壤到水稻的迁移和积累。研究结果主要分成四个部分。.首先，考察了微生物燃料电池对土壤微生物和成分的影响。结果表明微生物燃料电池的阳极会显著改变阳极及附近土壤的微生物群落结构；当电池负载较低时，能促进阳极呼吸菌的生长。对于无机成分，随着电池的运行，阳极快速消耗土壤中的有机质，同时导致酸化。.其次，重点考察了微生物燃料电池对铁砷释放的影响。我们发现，土壤可溶有机质是控制铁还原及砷释放的关键因素。当有机质含量较低时，阳极微生物和土壤铁还原菌竞争有机底物，抑制铁还原过程，造成砷释放变慢；当有机质含量较高时，竞争机制不占主导，土壤酸化和土壤铁还原菌的增加，是造成铁砷释放加速的主要因素。对于有机质过高的土壤，可以通过干湿交替处理，快速降低土壤微生物可利用的有机质，从而再次得到有机底物竞争环境，从而控制砷释放。.再次，深入研究了微生物燃料电池影响下，重金属从土壤到水稻的全过程。微生物燃料电池对水稻生长无负面影响，并且可以显著降低水稻各部分的As，Cu，Cr，Ni，Cd，其中在最重要的谷粒部分，施加sMFC可以降低这些有害重金属元素约40%。.最后，在研究电极与土壤-植物体系的过程中，我们认识到界面过程是阐明元素在土-水-植物体系的迁移转化机理的关键，而界面过程研究的瓶颈在于相关技术的缺乏。因此，我们开发了一种新型的高精度土壤孔隙水采样技术，可用于对土壤界面过程的深入研究。.综上所述，本项目系统地研究了微生物燃料电池对土壤重金属行为的影响过程和主要控制因素，其结果可以用于对于中轻度砷污染土壤的控制，为解决中国砷污染问题提供新的解决途径。