采用膜污染指数评估天然有机物在低压超滤膜中的污染行为

针对超滤膜的过滤特性,采用膜污染指数（FI）来研究天然有机物（NOM）的膜污染行为.实验中,腐殖酸（HA）、牛血清蛋白（BSA）以及海藻酸钠（NaAlg）被用作模型有机物进行超滤膜污染研究.结果表明,NOM-膜滤先后经过快反应和慢反应污染阶段,其中快反应膜污染指数（TFIF）远大于慢反应膜污染指数（TFIS）.说明短时间内NOM容易在低压膜上积累,造成通量迅速下降,引起较为严重的污染.因此,反应最初阶段,低压膜与有机物的作用决定了整个膜污染的趋势.经过水力清洗,通量有一定恢复,膜阻力降低,能够去除部分污染物,但仍有少量有机物附着在膜丝,从而造成不可逆污染.3种有机物造成的不可逆污染比例依次为BSA〉HA〉NaAlg,而通过化学清洗后,其不可逆污染比例依次为：NaAlg〉BSA〉HA,腐殖酸和蛋白容易造成不可逆污染,但碱洗易于除去,多糖造成的不可逆污染相对较轻,但碱洗难以去除.污染物与膜之间的相互作用可能是造成污染的主要原因.总的说来,FI计算方法简单,能够综合描述膜污染情况,具有一定的应用价值.

A Novel Approach of Using Fouling Index to Evaluate NOM Fouling Behavior During Low Pressure Ultrafiltration Process

In this study, fouling index (FI) was introduced as a novel approach to investigate NOM fouling behavior during low pressure membrane ultrafiltration process. Three kinds of typical NOMs, humic acid (HA), bovine serum albumin (BSA) and sodium alginate (NaAlg), were used in the experiments. The results indicated that the fouling caused by NOM can be considered as two steps with different FI values. One is the fast fouling phase, and the other is the slow phase. Apparently, the total fouling index of the fast phase (TFI_F) was much greater than that of the slow phase (TFI_S), which means the initial interaction between NOM and membrane would play a significant role in the whole fouling process. A higher TFI_F could lead to a faster fouling and the flux would decline more rapidly. After hydraulic washing, the flux was recovered and the resistance was reduced, indicating that physical cleaning could remove a part of foulants. Additionally, the results also represented that the sequences of NOM causing irreversible fouling and chemical clean irreversible fouling were BSA>HA>NaAlg and NaAlg>BSA>HA, respectively. Humic acid and protein tended to cause irreversible fouling and were easily removed by alkaline cleaning, while irreversible fouling caused by polysaccharide was difficult to remove by alkaline. The main cause of membrane fouling may be the interaction between foulants and membrane, which needs further research. Generally speaking, FI with a simple expression would play a significant role to describe the membrane fouling.