碳纳米管预涂覆低压膜去除水中腐殖酸的机理研究

以腐殖酸（Humic Acid，HA）为研究对象，通过压力辅助过滤技术将碳纳米管（Carbon Nanotubes，CNTs）预涂覆在聚醚砜（Polyethersulfone，PES）平板膜表面，制备了CNTs预涂覆低压膜，分别考察了该膜在恒压和恒流实验中对HA的去除情况及其对膜污染的缓解作用.研究表明，CNTs预涂覆膜可以有效缓解基膜的污染，保证CNTs的分散性，增加PES膜表面预涂覆CNTs的投加量，有助于缓解膜污染的发生；采用径向尺寸小的CNTs制备出的预涂覆低压膜，其抗污染能力更佳.研究进一步采用恒流膜滤装置对膜滤过程的3个阶段（新膜过滤阶段、膜污染加速阶段、堵塞膜截留阶段）进行了模拟，考察了CNTs预涂覆低压膜对HA的去除机理.结果表明，新膜过滤阶段，CNTs预涂覆低压膜运行初期，CNTs的吸附性能对HA的去除起主导作用，HA去除率随过滤时间的增加而不断减小，吸附阶段CNTs预涂覆膜的跨膜压差（Transmembrane Pressure，TMP）始终保持在较低水平（不高于15 kPa），降低CNTs的径向尺寸和提高CNTs投加量，均有助于吸附去除HA；膜污染加速阶段，随着CNTs预涂覆膜进入膜污染加速阶段，HA的去除率由吸附阶段的不断降低开始出现上升拐点，TMP由于CNTs预涂覆膜的加快堵塞而不断升高；堵塞膜截留阶段，CNTs预涂覆低压膜在一定程度堵塞后，表现出截留去除HA的效能，且TMP仍保持在低压膜运行范围内，降低CNTs的径向尺寸，制备的预涂覆膜孔径小且分布均匀，有助于其提高截留去除HA的效能.整个恒流实验过程中，未负载CNTs的基膜对HA仅有微弱的吸附作用，且由于其较大的孔径，对HA的截留作用十分有限.本文通过对CNTs预涂覆低压膜吸附阶段和截留阶段的划分，明确了CNTs预涂覆低压膜在吸附饱和之后，能够有效截留水中HA，可作为水中腐殖质类污染物去除的一种有效手段.

Removal of aquatic humic acid by carbon nanotube modified low pressure membrane

Low-pressure membrane was prepared by pre-depositing carbon nanotubes (CNTs) on Polyethersulfone (PES) flat membrane using pressure-assisted membrane filtration technology. Under both constant-pressure and constant-flow condition, the CNTs modified low pressure membrane was evaluated for its effect on aquatic humic acid (HA) removal and fouling alleviation. The results showed that CNTs modified low pressure membrane can effectively alleviate the original PES membrane fouling, and membrane fouling was better controlled by increasing the dose of CNTs and using CNTs with smaller radial size under the premise that CNTs was good dispersed. To understand the mechanism of CNTs modified low pressure membrane on aquatic HA removal, constant-flow membrane filtration device was used to simulate the three phases of the membrane filtration process, including new membrane filtration phase, accelerated membrane fouling phase, and blocked membrane interception phase. The results revealed that in new membrane filtration phase, the adsorption performance of CNTs is the dominant mechanism for the removal of HA. The removal rate of HA decreased with the increase of filtration time and the transmembrane pressure (TMP) was always kept at a low level (not higher than 15 kPa). Reducing the radial size of CNTs and increasing the dosage of CNTs were both helpful to remove HA by adsorption. In accelerated membrane fouling phase, the removal rate of HA began to increase after the continuous decrease during adsorption phase. Besides, the TMP also increased due to the accelerated blocking of the membrane. In the blocked membrane interception phase, the CNTs modified low pressure membrane started to show the interception performance of HA. Nevertheless, its TMP was still kept within the operating range of the low-pressure membrane. Reducing the radial size of CNTs helped to keep a uniform CNTs distribution on low-pressure membrane surface, which helped to improve the efficiency of intercepting aquatic HA. During the whole constant-flow experiment, the original PES membrane without CNTs showed a weak adsorption effect on HA, and the retention effect on HA was also very limited for its larger pore size. Through dividing the filtration process of CNTs modified low pressure membrane into adsorption and interception phase, this paper clarified that the CNTs modified low pressure membrane could effectively intercept aquatic HA after the saturation of adsorption. Consequently, it could be used as an effective method to remove aquatic humic substances in water.