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 (AICI(3)) or polyaluminum chloride (PACI). For AlCI3 or PACI, 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 Al-ms (monomeric and small polymeric alum species) and Al-u species (i.e., solid phase Al(OH)(3)) gradually increased. A correlation was also observed between membrane flux and the proportions of Al-ms and Al-u Compared with AlCI3, much more serious membrane fouling was induced when BSA was coagulated with PACI, owing to the lower proportions of Al-ms and Al-u species in the PACI system. For AICI(3), the potential fouling mechanism was pore constriction or blocking when the proportions of Al-ms and Al-u were lower than 62.3 +/- 5.1% (pH 6.0), followed by cake layer as the main fouling mechanism. For PACI, however, pore constriction or blocking occurred when the proportions of Al-ms and Al-u were lower than 35.4 +/- 3.2% (pH 6.5), and cake layer gradually became the main fouling mechanism. (C) 2015 Elsevier B.V. All rights reserved