[Experimental study of adhesion properties between membrane surface and humic acid during microfiltration]

To further unravel the humic acid (HA) fouling mechanism during microfiltration under different conditions, such as pH, ionic strength, the concentration of calcium ions, atomic force microscopy (AFM) combined with self-made PVDF colloidal probe was applied to determine the relationship between the adhesion forces of membrane-HA or HA-HA and the flux decline of membrane. The results indicate adhesion forces were the main reason of membrane fouling. With the decrease of pH or increase of the ionic strength, due to the electrical neutralization caused by pH and electrical shielding effect of ionic strength, the adhesion forces of membrane-HA and HA-HA increased. Because of the comprehensive effect of "salt bridge" and electrical neutralization, there was a transition from increase to decrease for the adhesion forces of membrane-HA and HA-HA as the doses of calcium ions increased. In all cases, both of membrane-HA and HA-HA adhesion forces had the same variation tendency, which displayed a good correlation with the flux decline trends during fouling experiments, respectively, and provided certain theoretical support to further understand the formation mechanism of membrane fouling.