微絮凝对腐殖酸超滤过程膜污染的减缓特性

以硫酸铝[Al_2(SO_4)_3·18H_2O]为絮凝剂,腐殖酸(humic acid,HA)和高岭土(Kaolin)水溶液为原水,研究微絮凝过程产生的不同絮体形态,对自制聚偏氟乙烯(PVDF)超滤膜过滤过程的影响.主要考察了微絮凝过程中絮体的特性(粒径大小及分布,分形维数)以及不同条件下形成的絮体形态对膜通量的影响,利用扫描电镜(SEM)和原子力显微镜(AFM)对污染膜的表面形貌进行表征,并测定了PVDF膜与有机污染物之间黏附力大小,来解析不同絮体形态对超滤膜的膜污染影响机制.结果表明,Al~(3+)以电性中和作用水解去除有机物,随着絮凝剂投加量的增加,絮体粒径不断增大,絮体的分形维数减小.膜通量衰减速率与絮体的粒径呈负相关,絮体粒径越大,膜通量衰减速率越小,超滤过程中形成的滤饼层越疏松,同时,较小分形维数的絮体引起的膜污染较轻,其膜通量恢复率也较高.PVDF-有机污染物之间的相互作用力大小与运行初期相应污染膜通量衰减速率呈正相关.当Al~(3+)投加量为5 mg·L~(-1),初始pH=7时,HA去除率为96.7%,膜通量衰减最小,通量恢复率达到88%.

Reducing Membrane Fouling from Micro-Flocculation in a Humic Acid Ultrafiltration Process

This study investigated the influence of different floc morphologies produced by micro-flocculation process on filtration of a self-constructed polyvinylidene fluoride (PVDF) ultrafiltration membrane. Aluminum sulfate was used as a flocculant and humic acid (HA) and kaolin as raw water. Both the properties of flocs formed during the micro-flocculation process (floc size and distribution, fractal dimension) and the effects of floc formation on membrane flux under different conditions were investigated. The surface morphology of the contaminated membrane was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and adhesion between the PVDF membrane and organic pollutants was measured to analyze the membrane fouling mechanism. Results showed that the main mechanism during a micro-flocculation process using Al³⁺ as a flocculant is electrical neutralization to remove organic matter. With an increase in flocculant dosage, floc size increased and the fractal dimension of flocs decreased. The attenuation rate of membrane flux was negatively correlated with floc size. The larger the floc, the lower the membrane flux attenuation rate, and the looser the filter cake layer formed during the ultrafiltration process. Comparatively, membrane fouling caused by flocs with smaller fractal dimension was lighter, and the membrane flux recovery rate was also higher. The interaction force between PVDF and organic matter was positively correlated with the corresponding membrane flux attenuation rate during the initial stage of operation. When dosage of Al³⁺ was 5 mg·L^-1 and initial pH was 7, the HA removal rate was 96.7%, the membrane flux attenuation rate was lowest, and the flux recovery rate reached 88%.