用微观作用力解析无机离子对腐殖酸的膜污染行为影响

Analysis on influence of inorganic ions on ultrafiltration membrane fouling behavior of humic acid via interaction forces

基于Na+、Ca2+离子在天然水体中的普遍存在及对超滤膜有机污染行为的影响,本研究主要考察了不同离子条件下腐殖酸(HA)对PVDF超滤膜污染行为的影响机理。使用原子力显微镜结合自制的膜材料及污染物探针定量测定了不同离子条件下PVDF-HA及HA-HA之间的相互作用力,同时进行了相应的膜污染实验及定量研究腐殖酸的去除效果。结果表明,PVDF-HA及HA-HA之间的相互作用力大小与膜污染速率及污染幅度呈正相关关系。一价Na+离子通过电荷屏蔽可降低HA表面的带电量,对HA膜污染行为及PVDF-HA及HA-HA之间作用力的影响并不明显。二价Ca2+离子通过电荷中和作用大幅度降低了HA表面的有效带电量,使得PVDF-HA及HA-HA之间的粘附力增大,加剧了膜污染速率。而过多的Ca2+离子会加剧HA之间的聚合,降低了HA进入膜孔内的机率,虽然会短暂的增加腐殖酸的去除效率但无法从根本减轻膜污染。

Based on the fact that the ubiquity of Na+and Ca2 +in natural water and its effect on ultrafiltration membrane fouling,the fouling behaviour of humic acid(HA) in PVDF ultrafiltration membranes under different ionic conditions were investigated.The interaction forces of membrane-foulant and foulant-foulant were investigated by atomic force microscopy(AFM) in conjunction with self-made PVDF colloidal probe and foulantcoated colloidal probe,respectively.Fouling experiment and HA removal rate under different ionic conditions were carried out.Results show that the interactions of PVDF-HA and HA-HA were in proportion to the membrane fouling rate and fouling extent.The influence of Na+on membrane fouling was insignificant although the net charge of HA molecule was reduced due to the charge screening of Na+.However,the flux decline rate and PVDF-HA and HA-HA interaction forces increased greatly with the increase of Ca2 +concentration,this may due to the charge neutralization of HA by Ca2 +.Moreover,the removal rate of HA increased and membrane fouling was mitigated with excess Ca2 +.