摘要
Calcium-humic acid (Ca-HA) complexes, known as non-rigid colloids in contrast to rigid SiO 2 ones, have been widely chosen as the target material to study the fouling behavior in filtration process. Although the influence of individual factors such as calcium concentration, pH, operation pressure, and ionic strength have been extensively investigated, only a few studies were dedicated to exploring their interplay consequences, particularly the size effect on the performance of nanofiltration. In this study, the size of Ca-HA complexes was finely adjusted by controlling the pH and calcium concentration and its consequence on the performance of nanofiltration was investigated. It was noted that there existed a critical size of Ca-HA complexes around 400–500 nm, where the degree of flux decline in a system containing larger Ca-HA complexes would rebound to a level similar to that of smaller complexes. This phenomenon was accompanied with the transition from cake formation to intermediate blocking, while the charge in Ca-HA complexes and membrane surface presents pronounce influences. Our results further suggested that in addition to the size effect, intermolecular interactions play an of particularly important role in nanofiltration, presumably through changing the local size of Ca-HA complexes by the relatively mobile Ca ions in the fouling layer.