膜蒸馏脱盐中膜污染与膜润湿的研究进展

Research progress of membrane fouling and wetting in membrane distillation process for desalination

膜蒸馏作为一种脱盐的新兴技术受到广泛关注。然而,因为实际水质组分复杂,可能含有如表面活性剂、油类物质、易结垢盐和有机溶剂等污染物,导致一般疏水膜在长时间运行情况下极易发生膜污染或者膜润湿,最终造成膜通量或截留性能降低。本文首先简述了不同种类的膜污染和膜润湿的特点及形成原因,并分析了膜污染和膜润湿之间的区别和联系。对膜蒸馏过程中膜污染和膜润湿的监测和预测手段进行了简要介绍,最后针对膜蒸馏脱盐过程,重点介绍了近几年国内外预防膜污染和膜润湿的研究进展。研究者一般从污染物与疏水膜的相互作用力着手对疏水膜进行表面改性制备全疏膜和Janus复合膜,避免污染物在膜面的吸附以及抑制表面或孔道润湿。越来越多的研究人员采用致密亲水膜的渗透汽化脱盐来从根本上避免疏水膜带来的润湿。除此之外,对进料液进行预处理也能显著延迟膜的污染和润湿,如混凝/沉淀、膜过滤、煮沸、pH调控等,还可通过改变进料方式、辅助外加磁场等措施控制膜表面局部区域的流体力学状态,减少污染物的附着。适当的膜后处理措施也能恢复膜性能。最后,文章指出了解决膜蒸馏中膜污染和膜润湿的研究方向。

Membrane distillation(MD)is a newly developing desalination technology.However,actual water contains complex composition such as surfactants,oils,easy scaling salts and organic solvents.Therefore,the traditional hydrophobic membrane is easily fouled or wetted during a long-term operation,which results in membrane flux or salt rejection rate decrease.The characteristics and types of membrane fouling and wetting were introduced in this paper.The differences and relations between fouling and wetting were also analyzed.The monitoring and predicting methods were briefly described during membrane fouling and wetting process.Finally,the research progress in preventing fouling and wetting was mainly introduced.By considering the interaction between pollutants and hydrophobic membrane,the researchers usually modified the surface of hydrophobic membrane to develop omniphobic and Janus composite membranes.Those novel membrane surfaces could avoid the adsorption of pollutants and inhibit wetting.In recent years,pervaporation was also studied in desalination to control membrane fouling and wetting,in which dense hydrophilic membrane was adapted.In addition,feed pretreatment could significantly delay fouling and wetting,such as coagulation/precipitation,boiling,membrane filtration,pH control,etc.Various feeding modes,external magnetic field and microwave radiation were investigated to control the local hydrodynamics boundary condition near the membrane surface and to reduce the adhesion of pollutants.The membrane performance could be recovered after proper post-treatment.Finally,the research direction on membrane fouling and wetting in MD process were pointed out.