溶解性有机物-无机盐共存体系中PFASs的NF分离特征及机制研究

Because of the limitation of conventional water treatment processes, perfluoroalkyl and polyfluoroalkyl substances (PFASs) are frequently detected in drinking water and seriously threaten human health. Nanofiltration (NF) is a efficient technology to remove micromolecular organic pollutants from water. Based on the water quality characteristics that dissolved organic matters coexist with inorganic salts in practical raw water, this project is proposed to investigate the macroscopic NF separation characteristics of representative PFASs which are prevalent in micro-polluted waters. Moreover, self-developed NF membrane material wafers and quartz crystal microbalance with dissipation monitoring (QCM-D) will be combined to quantitatively characterize the combination tendency between two solutes as well as between each solute and membrane surface which influence the removal efficiencies of PFASs from microcosmic level. Furthermore, the characteristics of the NF membrane zeta potential and PFAS charge, the relationships between PFAS molecular dimension and the membrane pore size, and the characteristics of PFASs adsorption and the fouling layer structure will be combined together for the following analyses. The influencing mechanisms of coexisted matters on the separation of PFASs will be recognized. The contributions of electrostatic repulsion, size exclusion, adsorption, and cake enhanced concentration polarization effects to the rejection of PFASs will be clarified. In addition, the preponderant influence factors on the separation of typical PFASs and the predominant NF retention mechanisms of representative PFASs in the dissolved organic matters and inorganic salts coexisting system will be revealed. The ultimate goal is to propose the high efficient PFAS separation strategy and provide theoretical basis for the practical application of NF to guarantee the drinking water safety.

由于常规水处理工艺的局限性，全氟化合物（PFASs）在饮用水中频繁检出并严重威胁着人体健康，而纳滤（NF）正是去除小分子有机污染物的高效技术。本课题针对微污染水中的典型PFASs，基于实际原水中溶解性有机物与无机盐共存的水质特征，考察典型PFASs的宏观NF分离规律；利用研发的NF膜材料芯片结合QCM-D，从微观尺度量化表征影响PFASs分离效能的各物质之间及其与膜面的结合趋向。并综合NF膜Zeta电位和PFASs荷电特征，基于PFASs分子尺寸和膜孔径的大小关系，结合PFASs吸附情况和污染层结构特征等，识别共存物质影响PFASs分离的作用机制，辨明静电排斥、空间位阻、吸附及污染层强化的浓差极化等作用对PFASs截留的贡献，揭示溶解性有机物-无机盐共存体系中典型PFASs分离的优势影响因素和主导NF截留机理。从而提出PFASs的高效分离策略，为NF保障饮用水安全的实践应用提供理论支撑。

全氟化合物（PFASs）具有持久性、生物富集性和生态毒性。天然水体是PFASs在环境中赋存和迁移的主要介质。因独特的选择性分离能力，纳滤技术在水中PFASs去除中具有极大的应用潜力。由于常规饮用水处理工艺对溶解性有机物和无机离子的去除效果非常有限，因此它们普遍共同赋存于纳滤待处理原水中。据此，本研究系统考察了溶液特性、水中常见无机离子和典型溶解性有机物单独以及二者协同影响下，典型PFASs的纳滤去除规律。探明共存物质影响PFASs分离的作用机制，典型PFASs的主导截留机理和优势影响因素。研究结果表明，溶液特性，共存离子和溶解性有机物荷电情况，PFASs、共存物、纳滤膜三者之间的相互作用，污染层的结构，纳滤膜的截留分子量（MWCO）、荷电特征，PFASs的分子量、官能团等因素，对PFASs的去除和主导截留机理起决定性作用。筛分作用、静电排斥作用以及污染层的“附加”截留或者污染层强化的浓差极化作用（CECP）等是决定PFASs长期稳定截留率的关键作用，而主导机理因纳滤膜、共存物以及PFASs不同而有所差异。由于大多数PFASs在天然水环境中荷负电，与常用纳滤膜带电性相同。因此，当PFASs的分子量小于纳滤膜的MWCO时，静电排斥作用通常决定PFASs的截留率，而当PFASs的分子量大于纳滤膜的MWCO时，筛分作用通常是主导截留机理。若膜面污染层发挥“活性截留层”的作用，则有利于PFASs截留，若其导致CECP作用，则不利于PFASs截留，具体情况与污染层结构和性质有关。基于以上研究结果，针对性地提出微污染原水中PFASs的纳滤高效分离策略。并创新性地将界面聚合法与层层自组装法有机结合，研制出一种适用于PFASs高效分离的纳滤膜。本项目研究为饮用水安全保障提供了科学依据和技术参考。