Comparison of membrane fouling induced by protein, polysaccharide and humic acid under sodium and calcium ionic conditions

To further compare the effect of sodium and calcium on the membrane fouling mechanism of typical organic matters, the adsorption behavior of sodium alginate, humic acid and bovine serum albumin on PVDF membranes were explored by quartz crystal microbalance and dissipation (QCM-D), while the adhesion force between foulants and between the foulants and membrane were examined by using atomic force microscopy (AFM) detection with foulant-coated probes. Results demonstrated that the adhesion force between organic and membrane had significant impact on the adsorption rate at the initial fouling stage, whereas the interaction force among the organic was connected with the degree of irreversible fouling and the structure of the fouling layer. Ca2+ made organic fouling more severe and irreversible due to the complexation effect under the same ionic strength conditions, which is consistent with the XDLVO theory. Compared to the other two organics, BSA demonstrated deposition more in mass, higher in adsorption rate and irreversibility under both Ca2+ and Na+ conditions, which attributed to stronger interaction forces among BSA molecules and the thus formed denser fouling layer. During the adsorption process the pseudo-second-order agreed well with fouling behavior of SA and BSA, while HA conformed to the pseudo-first order kinetic model.