磁树脂-超滤耦合净水工艺中不可逆有机物膜污染的减缓机制研究

Control of physically irreversible fouling caused by natural organic matter (NOM) is particularly important for the reduction of chemical cleaning in drinking water treatment by ultrafiltration. The applicants found that the physically irreversible organic fouling of the PVDF hollow fiber ultrafiltration membrane was markedly alleviated when the membrane module was submerged in the magnetic ion exchange resin (MIEX) contactor, i.e., in an integrated process of magnetic ion exchange resin and ultrafiltration. The reciprocating accumulation (filtrating) and stripping (backwashing) of MIEX slurry on and off the membrane surface worked as a dynamic membrane thereof and played an important role in the physically irreversible fouling control. In order to elucidate the underlying mechanisms, the applicants propose a comprehensive spatial and temporal analysis in this project, combining NOM removal in the bulk solution with dynamic membrane functioning at the membrane surface as well as the filtration procedure with the backwash procedure. The effects of NOM removal by MIEX on physically irreversible fouling control will be analyzed. The functions of MIEX dynamic membrane on the fouling layer component and structure together with its affinity with the PVDF membrane will be determined. The overall mechanisms involved in the mitigation of physically irreversible organic fouling in the integrated MIEX and ultrafiltration process will finally be revealed with respect to the pre-removal, dynamic membrane functioning, and enhanced backwashing. These results will theoretically contribute to the application of MIEX for physically irreversible fouling control and chemical cleaning reduction, and powerfully promote the wide use of the integrated process of MIEX and ultrafiltration for drinking water treatment.

减缓由天然有机物（NOM）引起的水力不可逆膜污染是降低超滤净水工艺中化学清洗频率的重要途径。申请人发现，将PVDF中空纤维超滤膜置于磁树脂（MIEX）搅拌池中的一体式MIEX-超滤耦合工艺，可以有效减缓不可逆有机物膜污染；膜表面存在的MIEX堆积（过滤时）和剥落（反洗时）往复"动态膜"过程在其中发挥着重要作用。为阐明其机理，申请人提出从溶液本体NOM去除和近膜壁处动态膜调节两处作用空间、过滤和反洗两处作用时间入手，解析MIEX去除有机物与不可逆膜污染控制间的内在联系，明确MIEX动态膜对近膜壁处滤饼层成分、结构及与PVDF膜面间亲和力的调控规律，系统阐释MIEX及其动态膜减缓不可逆有机物膜污染的"交换预拦截-动态膜调节-强化水力反洗"三方面作用机制。研究成果将为利用MIEX有效控制超滤不可逆膜污染，减少化学清洗提供可靠的理论依据，进而推动MIEX-超滤耦合工艺在饮用水处理中的广泛应用。

有效控制天然有机物（NOMs）引起的不可逆膜污染是保障超滤净水工艺稳定运行的关键因素。本项目构建了NOMs分子量和亲疏水性分级制备方法，解析不同NOMs组分与不可逆膜污染之间的关系，指明>3kDa HiM，<3kDa HoA和>3kDa HoB三种组份对不可逆超滤膜污染影响最严重。通过分体式和一体式两种MIEX-UF耦合工艺对比发现，一体式工艺减缓不可逆膜污染的效果更突出，可使膜的化学清洗频率降低73%。机理分析如下：首先，MIEX能够从溶液本体中有效吸附去除<3kDaHoA和>3kDaHoB两种典型不可逆膜污染组分，对减缓膜的长期不可逆污染具有一定作用；其次，MIEX颗粒对超滤膜面的刮擦作用对减缓膜不可逆污染贡献较小，膜面形成的MIEX动态膜是一体式工艺减缓膜污染的关键。以聚苯乙烯微球修饰原子力探针，构建了“污染物-MIEX”和“污染物-PVDF膜”之间的微观界面作用力测定方法，发现不可逆膜污染物与MIEX之间的亲和力明显大于与PVDF膜之间的亲和力，从而促使污染物在膜面和树脂颗粒表面进行二次分配，减少了到达膜面或进入膜孔的污染物量；最后，MIEX动态膜有利于强化水力反洗。树脂层的存在改变了膜面凝胶层的结构，不再形成致密的凝胶层，而且污染物与树脂之间更强的亲和力会减弱凝胶层与膜面的结合程度，使其更易于在水力反洗时被去除。同时，水力反洗研究发现，树脂的磁凝聚效应促使其在膜面形成，反洗时树脂层成片脱落，促使膜上的污染物一起离开膜面，从而达到强化水力反洗的效果。本项目对一体式工艺的典型工艺参数进行了优化，为推动MIEX-UF一体式工艺在饮用水处理领域推广应用奠定了理论基础。