污水体系中微生物胞外聚合物对鸟粪石矿化的影响机制研究

Struvite crystallization from wastewater especially reject water is an effective way to recover nitrogen and phosphorus, but there is an organic matter disturbance problem that reduces the efficiency of the crystallization process and the quality of the recovered product. The previous studies are less concerned about the impact of organic matter on struvite mineralization, making the struvite mineralization in the "out of control" state. This project will choose microbial extracellular polymeric substances (EPS), the main components of organic matter in the reject water, to carry out the struvite mineralization experiments. The impact of EPS on the nucleation and growth kinetics of struvite will be analyzed to understand the influence mechanism of EPS on the crystallization efficiency of struvite. The nucleation process of struvite on EPS will be characterized to reveal the microcosmic mechanism of EPS to control struvite nucleation. The mode of action between EPS and struvite surface and the occurrence state of EPS on struvite crystals will be investigated to reveal the microscopic mechanism of EPS controlling the morphology and structure of struvite and reducing struvite purity. The effect of EPS on the surface potential of struvite will be studied to find out the influence mechanism of EPS on the accumulation and deposition of struvite. The effect of EPS on struvite dissolution will be studied to find out the way and mechanism of EPS to promote struvite dissolution. The obtained results are helpful to systematically understand the effect of EPS on struvite mineralization in the reject water and provide guidance for the development of struvite crystallization process in experimental mineralogy.

从污水尤其是污泥水中结晶鸟粪石是氮磷回收的有效途径，但存在有机物干扰问题，这降低了鸟粪石结晶工艺的效率和回收产物的品质。已有的研究较少关注有机物对鸟粪石矿化的影响，这使得鸟粪石矿化处于“失控”状态。本项目选择污泥水中有机物的主要组分微生物胞外聚合物(EPS)开展鸟粪石矿化实验。通过分析EPS对鸟粪石成核和生长动力学的影响，了解EPS对鸟粪石结晶效率的影响机制。表征鸟粪石在EPS上的成核过程，揭示EPS调控鸟粪石成核的微观机制。考察EPS与鸟粪石晶面作用的方式和在鸟粪石上的赋存状态，揭示EPS调控鸟粪石形貌结构和掺杂鸟粪石的微观机制。研究EPS对鸟粪石表面电势的影响，查明EPS影响鸟粪石聚集和沉降的机制。研究EPS对鸟粪石溶解作用的影响，查明EPS促进鸟粪石溶解的方式和机制。成果的取得，有助于系统理解污泥水中EPS对鸟粪石矿化的影响，为发展鸟粪石结晶工艺提供实验矿物学上的指导。

通过鸟粪石结晶从污水中回收氮磷是污水处理技术的新发展方向。作为鸟粪石结晶最理想的媒介，污泥水中不仅含有高浓度的氮磷，还含有大量的有机物，其主体是微生物胞外聚合物(EPS)，但目前尚无研究关注污水中微生物EPS对鸟粪石矿化的影响。本项目首先选择微杆菌属H207为模式菌株来研究微生物及其EPS在鸟粪石形态演化中的作用。原位矿化结果显示，随着矿化时间的延长，鸟粪石形貌发生明显演化。最初表现为浮生结构，之后经过棺材盖状转变为四角板状，最终形成X形鸟粪石。仿生矿化结果表明，溶解态EPS调控形成了初始浮生结构。之后，鸟粪石沿b轴取向生长，形成棺材盖状形貌。随着矿化时间进一步延长，鸟粪石发生溶解再沉淀，晶体沿顶角方向生长，逐步演化为X形鸟粪石。该工作进一步揭示了细菌成因鸟粪石的形貌演化机制，阐明了EPS在调控鸟粪石形貌形成中的独特重要作用。微生物EPS仍然是相对复杂的混合物，本项目还选择与EPS具有相似结构和性质的海藻酸钠作为EPS模型物，在模拟污水中研究EPS对鸟粪石结晶的影响。浓度序列实验显示，随着海藻酸钠浓度增大，鸟粪石尺寸和产量明显减小，说明海藻酸钠能够有效抑制鸟粪石生长。相比于不添加海藻酸钠时获得的不规则长板状鸟粪石，海藻酸钠存在下鸟粪石表现为规则的棺材盖形结构，并且往往形成双晶，说明海藻酸钠能够影响鸟粪石的形貌形成和聚集组装。通过一系列表征发现，海藻酸钠通过羧基等官能团与鸟粪石特定晶面结合，实现对鸟粪石形貌和生长的调控。同时，我们还发现，随着pH和镁磷比的增大，鸟粪石尺寸明显增加，说明增大镁磷比和提高pH有利于削弱海藻酸钠的抑制作用。上述研究揭示了模型EPS对鸟粪石结晶生长的影响机制，初步探究了削弱EPS不利影响的可能策略，研究成果对从富含有机质的污水中回收鸟粪石具有指导意义。

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