[Fouling behavior of sodium alginate during microfiltration at various ionic compositions: XDLVO approach]

The extended Derjaguin-Laudau-Verwey-Overbeek (XDLVO) theory was utilized to quantitatively evaluate short-range interfacial interactions involved in microfiltration (MF) membrane fouling by sodium alginate (SA) at various ionic compositions. Results showed that for hydrophilic membrane surfaces, van der Waals interactions facilitated fouling, whereas acid-base interactions alleviated fouling; for hydrophobic membrane surfaces, however, van der Waals interactions mitigated fouling and acid-base interactions turned out to be favorable for fouling. Electrostatic double layer interactions contributed minimally to fouling when SA molecules came into contact with MF membrane surface. Ionic strength and Ca2+ affected SA fouling of MF membranes mainly through alteration of acid-base interactions between membrane and SA or among SA themselves. Higher ionic strength could make acid-base interaction less repulsive or more attractive, thus aggravating SA fouling of MF membrane. Although Ca2+ accelerated flux decline significantly, Ca2+ could enhance physical cleaning efficiencies. Under all tested ionic compositions, fouling potentials (K) of initial and subsequent stages correlated well with membrane-SA interfacial free energy of adhesion and SA-SA interfacial free energy of cohesion, respectively. This implies that the XDLVO theory is applicable for description of MF membrane fouling by SA at various ionic compositions.