磁絮凝膜过滤工艺中附加磁场强化清洗

基于磁强化絮凝膜过滤(MEFMF)工艺中磁絮体和含磁滤饼层的特性,设计了在线(on-line)和离线(off-line)磁强化清洗(MEC)工艺.在磁场和曝气剪切的协同作用下,含磁滤饼层脱离膜纤维表面,膜通量恢复率较常规物理清洗(RC)明显提高.在离线磁强化清洗时,设计反洗装置中心的磁感应强度为6 mT,曝气强度为500 L·m^-2·min^-1,控制清洗时间为5 min,维持反洗压力0.04 MPa,可达到最佳的膜清洗效果,通量恢复率达97%以上.在外加磁场强化清洗过程中,滤饼层中的磁种发生磁化作用,滤饼层表现出微弱的宏观磁性,在磁场的作用下向磁极运动,使得膜通量恢复率明显提高.此外,在MEFMF工艺中采用间歇磁强化清洗,可以更加有效地去除引起不可逆膜污染的胶体和有机物,降低膜污染速率,减缓膜污染.

Enhanced magnetic cleaning in magnetic enhanced flocculation membrane filtration process

On the basis of the characteristics of magnetic flocs and cake layer in the magnetic enhanced flocculation membrane filtration (MEFMF) process, processes of on-line and off-line magnetic enhanced cleaning (MEC) were designed. Magnetic cake layer was separated from fiber surface under the synergistic effect of magnetic field force and aeration shear force, in which way the goal of optimization of membrane cleaning was achieved. The magnetic enhanced cleaning process was added to magnetic enhanced flocculation membrane filtration for off-line cleaning of fouled membrane module in MEFMF process. In the magnetic cleaning process with device's magnetic induction 6 mT, aeration intensity 500 L·m^-2·min^-1, washing time to 5 min, backwash pressure 0.04 MPa, optimum cleaning effect could be achieved for flux recovery rate over 97%. In the enhanced cleaning process with magnetic field the magnetic seeding in the cake layer was magnetized, rendering the cake layer weak macro magnetism. Under the effect of the attached magnetic field the magnetized cake layer moved to the pole, therefore, membrane flux recovery rate was increased significantly. Furthermore, on-line intermittent magnetic cleaning could be more effective in removing colloidal and organic pollutants on membrane surface in the MEFMF process. The colloidal and organic pollutants were the major pollutants blocking membrane pores and causing irreversible fouling. As a result, membrane fouling was mitigated during the entire process.