pH值对有机物(BSA)膜污染的影响

选用BSA(牛血清蛋白)代表有机污染物,使用QCM-D技术考察了BSA在PVDF膜面的吸附行为及吸附层结构随pH值的变化特征,并采用原子力显微镜定量测定了相应pH值条件下PVDF-BSA及BSA-BSA之间作用力,结合膜污染试验,解析pH值对有机物污染膜行为的影响机理.结果发现,在BSA的等电点,PVDF-BSA及BSA-BSA之间的静电排斥力最小,导致BSA迅速吸附累积于膜面,形成密实的BSA污染层,引起超滤膜通量大幅度衰减.当pH值偏离BSA等电点后,BSA间静电排斥力的增强有效削弱了BSA在膜面的吸附量,相应BSA污染层松散度增大,膜污染减弱.在实际的水处理中,通过适当的pH值调节,针对性将超滤膜及污染物调整至带有相同电性、并增大二者所带净电荷量,是减缓超滤膜污染的有效手段.

Effect of pH on UF membrane fouling of organic foulant (BSA)

Bovine serum albumin (BSA) was selected to represent the organic foulant, and the adsorption behavior of BSA on PVDF membrane surface and the features of the changes of the structure of the adsorption layers change at different pH was investigated by the quartz crystal microbalance with dissipation monitoring (QCM-D), and the quantitative determination of the interaction forces between BSA-BSA and PVDF-BSA at relevant pH values were measured by atomic force microscope (AFM), and the mechanism of the influences of pH on the membrane fouling behaviors of organic foulant were analyzed combined with the membrane fouling experiment. According to the results, at the isoelectric point of BSA, there was the minimal value of the electrostatic repulsive forces between BSA-BSA and between PVDF-BSA, a higher deposition rate of BSA was resulted on the membrane surface, and a denser BSA layer was formed, so the flux was declined most severely. As pH deviated from the isoelectric point, the membrane fouling and the deposition rate of BSA onto the membrane surface were mitigated, which was mainly due to the increase of electrostatic repulsion forces, accompanied by a “loose” BSA layer was formed. Therefore, it is important to adjust pH to control the net charges of foulants and membranes positively or negatively to the same level together with the increase of the net charges of the both, because it is one of the effective strategies for mitigation of membrane fouling.