预处理工艺控制膜污染试验及其机理分析

Experiment and Mechanism Analysis of Pretreatment Process Control Membrane Fouling

摘要:

探讨了3种不同预处理技术对延缓超滤膜污染的作用.试验表明，前臭氧+在线混凝+超滤（工艺1）、前臭氧+超滤（工艺2）、前臭氧+预氯化+超滤（工艺3）3种工艺超滤膜过滤的临界通量分别为86.5,59.8,68.1 L?(m2?h)-1.其中工艺1临界通量最大，且其稳定运行的时间最长（约190 h），能够在一定程度上控制膜污染，这主要是因为水中的有机污染物质通过“矾花”被吸附到胶体类颗粒物上，通过膜筛分截留，减缓了有机污染物质与膜表面的接触与相互作用.控制、缓解膜污染方面，工艺3效果最好，其原因是在NaClO作用下有机物分子特征改变，一方面降低膜的通量负荷，改变其亲疏水性，另一方面NaClO使得滤饼层的电负性增大，过滤截留物和溶解性有机物较易在水力冲洗中被冲掉，跨膜压差得到很好恢复.通过扫描电镜发现，超滤膜表面附着一层滤饼层，滤饼层较疏松，而膜孔已被污染物堵塞；红外光谱研究发现，超滤膜经过氧化预处理和化学清洗，膜表面的某些基团被氧化，膜表面特性被改变.

Abstract:

The roles of three kinds of pretreatment technology (ozone+online coagulation+ultrafiltration (process 1), ozone+ultrafiltration (process 2), and ozone+prechlorination+ultrafiltration (process 3)) in delaying the ultrafiltration membrane fouling were explored in this paper. The results show that the critical flux of three processes are 86.5, 59.8 and 68.1 L?(m2?h)-1, respectively. Of the three processes, the critical flux of process 1 is the largest, with the longest stable operation time (about 190 h), and can control membrane fouling to a certain extent. This can be explained by the adsorption that organic pollutants are adsorbed by colloidal particles, which can reduce the contact and interaction between organic pollutants and membrane interface by the membrane sieving intercept. Process 3 is followed with the best performance in controlling and alleviating membrane fouling due to the change of organic molecular characteristics under the effect of NaClO: 1) membrane’s flux declined and hydrophilichydrophobic property changed; 2) the increasing electronegativity of cake layer promotes the waterbackwash to remove the remaining matters and dissolves the organic matter, which results in a good transmembrane pressure recovery. By scanning with the electron microscopy (SEM), it is found that the soft filter cake layer is adhered on the surface of the ultrafiltration membrane and membrane hole is blocked by pollutants. The infrared spectroscopy study finds that the membrane surface properties are changed as some groups on membrane are oxidized by oxidation pretreatment and chemical cleaning.