Effect of aluminum speciation on ultrafiltration membrane fouling by low dose aluminum coagulation with bovine serum albumin (BSA)

Abstract

Up to now, many studies have focused on ultrafiltration (UF) membrane fouling when sweep flocculation is the main coagulation mechanism. However, there has been less focus on cases where charge neutralization is the main coagulation mechanism. Herein, UF membrane performance was investigated when bovine serum albumin (BSA) was coagulated with low dose aluminum chloride (AlCl3) or polyaluminum chloride (PACl). For AlCl3 or PACl, a large flux decline occurred at pH 5.5 and membrane fouling was steadily alleviated with increasing pH, resulting in a strong correlation between membrane flux and the corresponding solution pH. As pH rose, the proportions of Alms (monomeric and small polymeric alum species) and Alu species (i.e., solid phase Al(OH)3) gradually increased. A correlation was also observed between membrane flux and the proportions of Alms and Alu. Compared with AlCl3, much more serious membrane fouling was induced when BSA was coagulated with PACl, owing to the lower proportions of Alms and Alu species in the PACl system. For AlCl3, the potential fouling mechanism was pore constriction or blocking when the proportions of Alms and Alu were lower than 62.3±5.1% (pH 6.0), followed by cake layer as the main fouling mechanism. For PACl, however, pore constriction or blocking occurred when the proportions of Alms and Alu were lower than 35.4±3.2% (pH 6.5), and cake layer gradually became the main fouling mechanism.