PTFE超滤膜对水中三种典型天然有机物的去除及其膜污染机制

Removal of Three Typical Natural Organic Matters in Water by PTFE Ultrafiltration Membrane Process and the Mechanism of Membrane Fouling

研究聚四氟乙烯(PTFE)超滤膜对水中天然有机物的去除效果以及膜污染机制。天然有机物是膜污染中的主要污染物,其中腐植酸(HA)、海藻酸钠(SA)和牛血清蛋白(BSA)为典型的代表。过滤试验采用序批式,配制特定浓度的天然有机物水样进行死端过滤。通过采用紫外分光光度计和TOC-L仪测定水样的UV和总有机碳的值来评估PTFE对三种天然有机物的去除效果,同时采用扫描电子显微镜(SEM)对污染后的膜表面进行观察以推断其污染机制。此外,在HA原料液中添加钙离子(Ca^(2+))和鸡蛋白溶菌酶(LYS,带正电)进行过滤试验,探究PTFE对带不同电荷有机物的去除效果和超滤膜的污染机制。PTFE超滤膜对三种典型的天然有机物去除率以及膜污染情况不尽相同,对HA和SA的去除率远高于BSA,而对HA的去除率稍高于SA。HA和SA对PTFE的膜污染机制是先膜孔阻塞而后形成滤饼层,BSA则为膜孔吸附。PTFE对LYS的去除率几乎为零,但混合了HA和Ca^(2+)后的去除率显著升高,加入Ca^(2+)升高更明显,原因是Ca^(2+)与LYS不但有静电吸附作用,还有架桥作用,形成了更致密的滤饼层。

This experiment focuses on the removal and fouling effect of three typical natural organic matters （NOM） in surface water by polytetrafluoroethylene（PTFE） ultrafiltration membrane. NOM is the main pollutant in membrane fouling. Humic acid （HA）, sodium alginate（SA） and bovine serum albumin（BSA） are the three typical representatives. Experiment was operated in a dead-end filtration mode, by using of sequeneial batch type. Raw water was made of natural organic matter with certain concentrations. The removal effect of three typical NOMs by PTFE was examined by UV and TOC with ultraviolet speetrophotometer and TOC-L meter. Meanwhile, fouling behavior was inferred by observing the membranes fouled by NOMs using scanning electron microscope（SEM）. Besides, adding calci-um ions（ Ca2＋） and lysozyme （from chicken egg white, positively charged） was used to explore the removal and fouling behavior of NOMs with different charged. The removal efficiency and fouling effect of three typical NOMs by PTFE varied. The removal efficiency of either HA or SA was nmeh higher than BSA, while SA was just slightly lower than HA. The fouling meehanism of HA and SA was firstly pore plugging then the formation of cake layer, while pore adsorption for BSA. PTFE had nearly zero removal efficiency on LYS, but remarkably increased when HA or Ca2＋ was added. However, nmeh higher removal was gained by adding Ca2＋ due to the extra effect of bridging on the basis of electrostatic adsorption.