净水工艺中超滤膜氧化行为对其分离传质性能影响机理研究

In recent years, ultrafiltration (UF) technology has achieved a rapid development in our country. However, in practical applications i,e UF hybrid techniques, the impact of chemical agents on the structure and properties of the UF membranes was scarcely mentioned, which is a potential threat to the utilization of UF system. In this proposal, we focus on the typical hybrid coagulation-UF-chemical cleaning process, which offered us an opportunity to uncover the formation of hydroxyl radical from the catalytic reaction between the NaClO agent and the coagulation foulant (including metal coagulants and their hydrolyzate), and to reveal the effect of NaClO and hydroxyl radical on membrane materials. In this hybrid process, in order to reveal the change of membrane heterogeneous structure, we will also investigate the evolution of the polymers from their physicochemical properties, and the transformation of additives from their formation of occurrence. In addition, to insight into the evolution mechanism of membrane permeability in oxidation process, depending on the material characterization techniques and mass transfer model of pores, the relationship between pore resistance and membrane mesoscopic structures (including the hydrophobic structure and the electric effect of the polymers, and the blocks steric-hindrance effect of additives) will be explained. Moreover, in membrane oxidation process, the evolution of the interfacial interaction between membrane and foulant will be analyzed from hydrophobic interaction, electrostatic repulsion and hydration repulsion, which will illustrate the cooperation mechanism between pore size exclusion and interfacial interaction in membrane separation process. Therefore, we believe this proposal will provide a great chance to develop the separation and mass transfer theory in UF process, even to promote the application of UF technique in water treatment area.

近年来，超滤技术在我国已投入大规模应用。但在实际水处理组合工艺中，化学药剂投加对膜材料产生了强制氧化作用，是影响膜系统稳定运行的潜在威胁。本项目从以NaClO为代表的超滤膜化学清洗工艺出发，以“混凝-超滤”过程中混凝剂及其絮体在膜面的附着现象为切入点，通过研究金属混凝剂与NaClO接触时存在的催化反应，从而揭示膜法水处理过程中NaClO与羟基自由基对超滤膜非均相结构的协同氧化机理。同时，以超滤膜氧化过程中其过滤性能的变化为突破口，借助现代材料表征技术，解析氧化过程中聚合物物化特性、添加剂赋存形态的演化规律，探明聚合物疏水结构、荷电效应，添加剂链段位阻效应等介观因素对超滤膜传质阻力的影响机制；借助氧化过程中超滤膜表面特性的时序变化特征，阐明“膜/污染物”界面疏水相互作用、静电排斥作用、水合排斥作用在污染物分离过程中的协同原理，最终揭示实际应用中超滤膜性能演化机理、完善超滤膜分离传质理论。

本课题围绕膜法饮用水净化工艺中超滤膜氧化行为这一核心问题展开研究，以超滤膜“聚合物+添加剂”二元结构特征为基础，研究了二者物化特性与膜材料孔径结构、分离性能之间的协同演化机制及作用原理，并基于相关问题提出了对应的新型膜材料改性策略。一方面，通过揭示超滤膜氧化过程中添加剂的流失机理，量化分析了添加剂赋存形态（化学结构及其水合作用）与膜孔微观结构之间的构效关系，并通过构建多孔膜复合孔道模型，提出相对合成孔径（Relative Synthetic Aperture, RSA）可作为评价和预测复合膜材料长期性能的重要补充参数。同时，通过开发新型PLA-TiO2复合制膜添加剂，提出“有机-无机”杂化材料在超滤膜制备中可充分发挥不同片段的功能作用，从而实现分离膜结构、表面特性、功能稳定性同步优化。另一方面，项目基于以PVDF为代表的结晶聚合物氧化行为，阐明了聚合物晶体极性特征与膜材料表面物化特性的关联机制，并通过耦合“离子-偶极”作用和“聚合物-共聚物”分子相互作用，实现了PVDF多孔膜本征极性特征构建，所得膜材料表面供电子力参数提升约8倍，表现出了独特的抗污染特性和电活性。最后，项目基于“膜-水-污染物”相界面作用计算，系统性的分析了膜分离过程中界面极性作用力的形成机制及其对污染物环境界面过程的调控原理，揭示了污染物沉积进程及膜面出生污染层结构“预滤作用”对超滤膜分离传质性能的影响机制。项目研究成果在材料物化特性、污染物环境界面过程、膜法水处理工艺间建立了有效联系，有望为推动膜法水处理工艺的可持续发展提供一定的理论依据。