金属还原菌和零价铁对多溴联苯醚的协同降解机理研究

Polybrominated diphenyl ethers (PBDEs) are persistent organic pollutants and have increasingly attracted international attention because of their potential to impact the environment and human health. Zero-valent iron is capable of debrominating PBDEs into lower brominated congeners, but a polarizing hydrogen film and corrosion products is formed at the metal surface that protects zero-valent iron from further oxidation. Biodegradation is considered to be a promising way of removing PBDEs from the environment. However, microbiological degradation of PBDEs is a significant challenge owing to their hydrophobicity and chemical stability. It is found previously that the relatively hydrophobic metal-reducing bacteria and electron-active zero-valent iron have complementary advantages in PBDEs degradation, which will study in this project. This research involves scientific content about cell growth and hydrogen consumption of metal-reducing bacterium in relation to anoxic zero-valent iron corrosion coupled to deca-BDE degradation; impact of metal-reducing bacterium on the precipitation of corrosion products on the surface of zero-valent iron; production of relatively unstable and lower bromo congener of deca-BDE by zero-valent iron for metal-reducing bacterium; impact of zero-valent iron on the change in surface hydrophobicity and PBDEs degradation activity of metal-reducing bacterium. The research is expected to find a new mechanism of the synergistic degradation of PBDEs, and recognize the essential role of metal-reducing bacterium and zero-valent iron in promoting PBDEs degradation. It will lay a new theoretical basis for the pollution control and bioremediation of persistent organic pollutants.

水环境沉积物中持久性有机污染物多溴联苯醚的污染及危害日益凸现。零价铁有利于多溴联苯醚还原脱溴，但表面极性氢气膜和铁矿物的钝化会阻止零价铁继续氧化。微生物是还原矿化多溴联苯醚的关键力量，但多溴联苯醚的强疏水性和化学稳定性导致还原效率低。前期研究发现，较强疏水性的金属还原菌和化学性质活泼的零价铁在多溴联苯醚的协同降解中具有优势互补作用，可能是实现多溴联苯醚污染治理的有效途径。项目综合电子传递、胞外成分结构、代谢产物和表面疏水性四个方面，重点研究金属还原菌消耗零价铁氧化产生的氢气偶联还原多溴联苯醚而生长以及减慢零价铁表面铁矿物钝化的作用；零价铁产生相对不稳定的低溴代同系物被金属还原菌利用以及提高金属还原菌细胞表面疏水性而促进多溴联苯醚降解转化的作用。预期阐明金属还原菌和零价铁协同降解多溴联苯醚的新机理，揭示这种协同降解作用的本质，为水环境沉积物中持久性有机污染物的污染控制和治理提供新的理论指导。

本项目针对多溴联苯醚的强疏水性和化学稳定性，通过综合金属还原菌的较强细胞表面疏水性和零价铁的活泼化学性质的优势互补作用，克服其中生物利用过程长和零价铁易钝化失活的缺点，从而实现多溴联苯醚污染的有效降解。项目从代谢产物、铁矿物、细胞外膜通道蛋白和表面疏水性四个方面，重点研究了厌氧条件下金属还原菌解钝化零价铁以及零价铁强化金属还原菌表面疏水性而吸附降解多溴联苯醚的机制，补充研究了协同零价铁降解多溴联苯醚的微生物的多样性，以及有氧条件下多溴联苯醚代谢途径差异和铁还原菌解钝化零价铁的机制。结果发现了可以协同零价铁降解十溴联苯醚的微生物具有多样性，这些细菌大多具有铁还原或产酸功能；在厌氧条件下，十溴联苯醚在金属还原菌和零价铁协同作用下产生低溴代的同系物，金属还原菌通过铁还原和产酸功能解钝化零价铁并且偶联还原十溴联苯醚而获得能量生长，金属还原菌的细胞表面疏水性可被零价铁强化并且通过特定的细胞外膜通道蛋白实现十溴联苯醚的吸附降解；而在有氧条件下，十溴联苯醚在铁还原菌和零价铁协同作用下产生与厌氧条件不一样的羟基化、甲氧基化和羧基化代谢产物并且可以被菌体继续降解，铁还原菌在有氧条件下同样可以通过铁还原和产酸功能实现零价铁的有效解钝化及活性强化。项目阐明了金属还原菌与零价铁对多溴联苯醚的协同降解是一种与零价铁的直接化学作用截然不同的作用机制，两者的优势互补效应是促进十溴联苯醚有效降解的动力所在。厌氧及有氧条件下的协同作用都行之有效，这为实际环境中持久性有机污染物的污染控制和治理提供了新的理论指导。