锆改性沸石添加对湖泊沉积物-水界面氮磷迁移转化的影响研究

Eutrophication, characterized by excessive nutrient loading and harmful algae bloom, is a global environmental problem in lakes. Excessive nutrients such as nitrogen (N) and phosphorus (P) in lakes can lead to eutrophication, and internal loading from nutrients-enriched sediments is one of the primary origins of excessive N and P in water. It thus becomes necessary to control the release of N and P from the nutrients-enriched sediments in terms of controlling eutrophication. In situ treatment of sediments with sorbents, which involves introducing sorbent amendments into contaminated sediments that alter sediment geochemistry, increase contaminant binding, and reduce contaminant exposure risks to people and the environment, is a novel and promising approach for in situ sediment remediation that minimizes or eliminates some of the problems of the conventional techniques such as sediment dredging, aluminum treatment, calcium nitrate addition, and capping. Solid-phase sorbent products with a high adsorption capacity and fast adsorption rate for N and P are highly needed for the application of the in situ sorbent amendment technology to control the internal loading of N and P in lakes. Herein, a novel sorbent product, i.e., zirconium-modified zeolite (ZrMZ) was developed and proposed as a sediment amendment to control the internal loading of N and P in lakes. The objective of this study was to investigate the effect of ZrMZ addition on the migration and transform of N and P at the sediment-water interface of lakes. Firstly, a series of ZrMZ products were prepared by loading different amounts of the zirconium oxide on the surface of the natural zeolites, the thermal-treated zeolites, the microwave-treated zeolites, the sodium-treated zeolites, the calcium-treated zeolites, the acid-treated zeolites, and the zeolites treated by the combined modification procedures, and these ZrMZ products were characterized by X-ray diffraction (XRD), environmental scanning electron microscope (ESEM), energy dispersive analysis system of X-ray (EDAX), and nitrogen adsorption-desorption isotherm, etc. Secondly, the adsorption characteristics of ammonium, dissolved inorganic phosphorus (DIP) and dissolved organic phosphorus (DOP) from water on different ZrMZ products were investigated in a batch mode. Thirdly, the effect of the ZrMZ amendment on the flux of N and P from the lake sediment into the water column was investigated using a series of sediment remediation microcosm experiments. Fourthly, the adsorption/desorption characteristics of ammonium, DIP and DOP onto/from the raw and ZrMZ-amended sediments was comparatively investigated in a batch mode. Finally, the change in the fractionation and bioavailability of N and P in the lake sediments following amendment with ZrMZ was investigated using chemical extraction method. Results of this study will be helpful for the application of ZrMZ as sediment amendments to control the internal P loading of the eutrophic lakes.

控制沉积物氮磷释放对于水体富营养化防治至关重要。沉积物原位改良技术，即通过向沉积物添加吸附剂以降低沉积物中污染物向水体迁移风险，是近年来新出现的且极具应用前景的一种沉积物污染物释放原位控制技术。应用原位改良技术控制沉积物氮磷释放的一个关键技术问题是寻找安全高效的改良剂。本项目针对富营养化湖泊沉积物氮磷污染问题，研究开发一种利用锆改性沸石作为改良剂控制沉积物氮磷释放的新技术。本项目首先制备一系列锆改性沸石并对它们的结构进行表征，再确定锆改性沸石对水中氨氮、无机磷和有机磷的吸附效果及机制，进而筛选出最佳锆改性沸石。其次，考察锆改性沸石添加对沉积物氮磷释放通量的削减效果及机制。最后，考察锆改性沸石添加对沉积物氮磷吸附-解吸特征、赋存特征和生物有效性的影响。通过以上研究力图确定锆改性沸石添加对沉积物-水界面氮磷迁移转化的影响程度和机制，以期为利用锆改性沸石作为改良剂控制湖泊沉积物氮磷释放提供帮助。

控制沉积物氮磷释放对于湖泊富营养化防治至关重要。沉积物原位改良技术是近年来新出现的且极具应用前景的一种沉积物污染物释放原位控制技术。应用原位改良技术控制沉积物氮磷释放的一个关键技术问题是寻找安全高效的改良剂。本项目针对富营养化湖泊沉积物氮磷污染问题，研究开发了一种利用锆改性沸石作为改良剂控制沉积物氮磷释放的新技术。本项目主要研究了以下两部分内容。第一部分研究内容为锆改性沸石吸附氮磷的性能及机制，首先制备了纯的水合氧化锆，考察了溶液共存的Ca2+和Mg2+对不同沉淀pH值条件下水合氧化锆吸附水中磷酸盐的影响，深入探讨水合氧化锆的吸磷机理，再将水合氧化锆负载到天然沸石上制备得到了锆改性沸石，继而考察了锆改性沸石对水中氮磷的吸附特征，考察了沸石可交换阳离子对锆改性沸石吸附水中磷酸盐的影响，考察了腐殖酸负载对锆改性沸石吸附水中磷酸盐的影响，分析了吸附磷酸盐后锆改性沸石中磷的稳定性，最终确定了锆改性沸石吸附氮磷的性能，并阐明了相关的吸附机制。第二部分研究内容为锆改性沸石控制沉积物氮磷释放的作用机制，首先考察了锆改性沸石添加对上覆水和间隙水氮磷浓度的影响，确定了锆改性沸石添加对沉积物氮磷释放通量的削减效应，考察了锆改性沸石添加对垂直方向上沉积物DGT有效态磷分布的影响，考察了锆改性沸石添加对沉积物中氮磷赋存特征和生物有效性的影响，确定了锆改性沸石添加对沉积物中可移动磷和生物有效磷含量的钝化效应，考察了锆改性沸石添加对沉积物吸附水中氮磷的影响，最终阐明了锆改性沸石添加控制沉积物氮磷释放的作用机制。通过本项目的研究，确定了锆改性沸石添加对沉积物-水界面氮磷迁移转化的影响程度和机制，可以为利用锆改性沸石作为改良剂控制湖泊沉积物氮磷释放提供科学依据。