有机物对聚酰胺复合纳滤膜硫酸钙结垢的影响

为揭示不同有机物形成的污染层对硫酸钙在纳滤膜面结垢行为的影响,选用牛血清蛋白(BSA)、腐殖酸(HA)、海藻酸(SA)作为典型有机污染物对聚酰胺复合纳滤膜进行污染,之后进行硫酸钙结垢实验.利用扫描电镜(SEM)观察不同污染条件下的硫酸钙形态,采用原子力显微镜(AFM)结合自制的硫酸钙探针测定不同污染条件下膜-硫酸钙及硫酸钙-硫酸钙之间的作用力.结果表明:与新膜结垢相比,有机物吸附在纳滤膜上改变了膜面性质,影响硫酸钙晶体成核机理.3种有机污染条件下硫酸钙结垢污染程度为SAHABSA.这是因为SA与Ca~(2+)的相互作用可缩短硫酸钙晶体成核时间,增大晶体尺寸,导致纳滤膜通量迅速下降;HA与Ca~(2+)络合增大了结垢层的厚度和密实度,导致纳滤膜通量衰减较大;而BSA与Ca~(2+)的结合能力较弱,加上其特殊的心形分子结构,导致该情况下硫酸钙结垢程度弱于其他两种有机物条件.

Effects of organic matters on the gypsum scaling of composite polyamide nanofiltration membrane

In order to reveal the influences of fouling layers formed by different organic matters on gypsum scaling behaviors on the surface of nanofiltration membranes, bovine serum albumin (BSA), humic acid (HA) and alginate (SA) were chosen as typical organic foulants to contaminate the composite polyamide nanofiltration membrane, respectively. After that, the gypsum scaling experiment was conducted. The gypsum crystal morphologies of different fouling conditions were observed by scanning electron microscopy (SEM). The interaction forces of membrane-gypsum and gypsum-gypsum in different membrane fouling conditions were investigated by atomic force microscope (AFM) combined with self-made gypsum probe. The results indicated that, compared with the virgin membrane condition, the adsorption of organic foulants on nanofiltration membrane had changed the membrane surface properties and influenced gypsum crystal nucleation mechanism. The degree of gypsum scaling in three organic fouling conditions decreased in the order of SA>HA>BSA. These phenomena were likely due to the interactions between SA and Ca²⁺ which could shorten the nucleation time of gypsum crystals, enlarge the crystals size and result in the fastest membrane flux decrease. The complexation between HA and Ca²⁺ increased the thickness and compaction of scaling layer, leading to a relatively serious membrane flux decline. Besides, the weak Ca²⁺ combination ability and particular heart-shape molecular structure of BSA led to a less degree of gypsum scaling compared to the other two kinds of organic conditions.