MWCNTs预涂覆及预吸附处理缓解低压膜腐殖酸污染的机制研究

以腐殖酸(Humic Acid,HA)为研究对象,采用多壁碳纳米管(Multiwalled Carbon Nanotubes,MWCNTs)对聚偏氟乙烯(Polyvinylidene Fluoride,PVDF)平板超滤膜进行预涂覆改性处理,并与等量MWCNTs分散状态时吸附处理HA对膜污染的缓解效果进行了对比,考察了MWCNTs在处理HA过程中缓解膜污染的机制.同时,分析了MWCNTs投量和溶液离子变化对MWCNTs吸附及截留作用缓解膜污染的影响.结果表明,MWCNTs预涂覆与吸附相比,能够更有效地缓解膜污染,其中,分散剂为乙醇的MWCNTs预涂覆层对膜污染的缓解效果最好.增加MWCNTs投量不能无限地提高其对HA的吸附及截留效果;添加Na~+会造成MWCNTs对HA的吸附及截留效果变差;添加Ca~(2+)能够提高MWCNTs对HA的吸附及截留效果.膜表面污染照片及膜电镜观测结果表明,乙醇分散MWCNTs在超滤膜(UF)表面形成的预涂覆层呈均匀的层状结构,HA被拦截在MWCNTs层的多孔结构内,不易进入PVDF膜膜孔,反洗时易脱附,可逆性高;纯水分散MWCNTs在超滤膜表面形成的预涂覆层易于团聚,HA容易透过MWCNTs涂覆层进而堵塞PVDF膜膜孔,可逆性低;MWCNTs预吸附处理后形成MWCNTs和HA的包裹体,不经微滤膜滤除,会在PVDF膜表面产生复合污染.

Study on the mechanism of MWCNTs pre-deposition and pre-adsorption to reduce the LPM fouling of humic acid

Polyvinylidene fluoride (PVDF) flat ultrafiltration membranes was modified with multi-walled carbon nanotube (MWCNTs) to remove humic acid (HA). To understand the mechanism of MWCNTs on membrane fouling control in the removal of HA, the adsorption and the interception performances of the pre-deposited MWCNTs (MWCNTs layer) were systematically compared. Besides, the effects of MWCNTs dosage and solution ions were further analyzed. The results reveal that MWCNTs deposition was benefit for fouling control. The MWCNTs layer formed by using ethanol as dispersant had the optimal efficiency on fouling alleviation. Increasing the MWCNTs dosage can''t increase the adsorption and retention of HA indefinitely. The addition of Na⁺ will reduce, but Ca²⁺ can improve the adsorption and retention of HA by MWCNTs. The fouling membrane surface was observed with optical and scanning electron microscope. The results demonstrate that the pre-deposited MWCNTs dispersed with ethanol had a uniform layer structure. HA was retained in the porous structure of the MWCNTs layer and was difficult to enter the PVDF membrane pores. HA was easily desorbed easy desorption of HA during backwash improves the membrane''s reversibility. However, MWCNTs despersed with water were prone to aggregate. HA was tend to adhere on the PVDF membrane surface or enter into the pores of PVDF membrane, which reduced membrane reversibility. After pre-adsorption of HA by MWCNTs, complex pollution of MWCNTs/HA would form on the surface of PVDF membrane, if not removed by microfiltration.