沉积物中垂向运移对镧沸石控制内源磷效果的影响机制

In-situ inactivation is an important method for lake internal phosphorus loading control. The vertical transport behavior of inactivation agent driven by downwelling flow in sediment could influence the phosphorus inactivation effectiveness. However, the current understanding of this issue is not clear enough. This project try to elucidate the vertical transport behavior as well as its influencing factor of inactivation agent via laboratory experiment and numerical simulation, by the case of lanthanum modified zeolite (LMZ), a novel inactivation agent. Then, the changing dynamics of vertical distribution characteristics for different phosphorus species will be studied via 31P-NMR and phosphorus fraction extraction. The obtained results will be combined with the interaction analysis between LMZ and different phosphorus species, to clarify phosphorus binding capacity attenuation process of LMZ and its mechanism considering LMZ vertical transport. The effect of LMZ vertical transport on the release behavior of iron-bound phosphorus (Fe-P) from sediments under redox cycling will also be explored, and response of Fe-P-S coupling cycle to LMZ vertical transport will be investigated by Diffusion Gradient Thin-film, microelectrode and molecular biology analysis, to reveal the influencing mechanism of vertical transport on inactivation effectiveness. The project will provide theoretical and technical support for the further application of in-situ inactivation technology in lake internal phosphorus control.

原位钝化是水体内源磷控制的重要方法。沉积物中下行流驱动下钝化剂的垂向运移行为会影响其控磷效果，然而目前对此认识尚不够清晰。本项目拟以新型钝化剂——镧沸石为例，通过室内实验和数值模拟，考察其垂向运移行为特征及影响因素。在此基础上，采用31P核磁共振（31P-NMR）和磷分级技术，考察沉积物中磷形态垂直分布特征对镧沸石垂向运移的响应规律，探究镧沸石与不同形态磷的相互作用模式，从而阐明垂向运移下镧沸石控磷性能的衰减过程及机制。与此同时，以沉积物中最敏感的铁结合态磷为关注对象，采用扩散梯度薄膜（DGT）结合分子生物学手段，研究镧沸石垂向运移对沉积物中不同深度Fe-P-S耦合关系的影响，揭示垂向运移对铁结合态磷释放机制的影响。通过本项目，为原位钝化在水体内源磷控制中的进一步应用提供理论支撑。

本研究系统分析了镧沸石在沉积物内源磷控制过程中，沉积物-水界面磷的分子形态、有机质种类和共存重金属离子对其控磷性能的影响，分析了上述因素的交互作用机制，并通过多种手段从宏观和微观角度揭示了相应的机理。研究结果表明，镧沸石对正磷酸盐、甘油磷、AMP和ATP的最大吸附量分别为73.53、7.55、4.17和20.33mg/g。吸附过程分为快速吸附和缓慢平衡两个阶段，拟合发现准二级动力学模型更适用。三种磷的吸附效果均会随pH的升高而降低，GP和AMP吸附效果对pH升高的响应尤为明显。腐殖酸钠对三种磷的吸附均会产生显著的抑制。XPS结果表明，三种磷在镧沸石表面的吸附机制为化学配位，而非静电作用；拉曼光谱证实，非磷酸基团可能会“抢占”镧沸石表面的吸附位，最终导致磷吸附量的下降。镧沸石可以显著提升原沉积物（R-S）和去除轻组有机质沉积物（LFOR-S）的磷吸附能力，吸附能力在LFOR-S中可得到更好地发挥。在24h内，R-S和LFOR-S的磷释放量179.40和289.03mg/kg。温度从5oC上升到30oC时，镧沸石对R-S的磷释放控制率逐渐升高，而对LFOR-S的磷释放控制率由90%下降到76%后又回到原水平。镧沸石可将底泥中非稳定态磷转化为稳定态，但LFOR-S中减少的非稳定磷的并未完全转化为稳定态，而是进入了水相中使其磷释放量高于R-S，导致控磷效果变差。要实现对LFOR-S磷释放的有效控制，需增大镧沸石投量。吸附等温线表明，镧沸石对磷和锌的最大吸附量为2.31和0.373mmol/g。共吸附实验中磷的去除率始终高于90％，而磷共存会显着提高锌的去除率。XPS和拉曼光谱的结果表明，在共吸附系统中磷对镧沸石的亲和力远高于锌，部分锌原子会与已经吸附的磷络合形成磷桥连三元络合物。镧沸石对磷、锌和铅的Langmuir最大吸附量分别为53.76、27.70和123.45mg/g。预先吸附饱和Zn和Pb后，镧沸石对磷的最大吸附量轻微下降；对于Zn和Pb来说，预先吸附其他污染物会对其吸附能力造成明显的影响。镧沸石在实现底泥中磷赋存形态转化的同时，诱导了锌和铅向残渣态的演变。镧沸石的投加可以实现底泥中磷/重金属的同步钝化。