Biofouling is one of the major obstacles to the widespread application of membrane technology in water and wastewater treatment, and use of anti-biofouling membrane materials is an effective approach to suppress biofouling. In this study, anti-biofouling polyvinylidene fluoride (PVDF) membranes were prepared by blending quaternary ammonium compound (QAC). Effects of QAC dosages on the physicochemical properties and anti-biofouling behaviours of the modified membranes were systematically investigated. The results showed that QAC was successfully present on the membrane surfaces, as revealed by X-ray photoelectron spectroscopy, Zeta potential and contact angle analyses. Anti-fouling tests using individual organic model foulants showed that the modified membranes had higher membrane fouling rate against organic matters, which is consistent with the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. In contrast, the modified membranes demonstrated evident anti-bacterial behaviours when individual model bacteria were used, which cannot be evaluated by this theory. Interestingly, the modified membrane showed a clear anti-fouling activity in a membrane bioreactor (the sludge mixture contained both organic foulant and microorganisms), suggesting its concurrent efficiency in controlling fouling induced by both organic matters and bacteria. This might be attributed to the contact-killing effects of QAC and the dual interactions between bacteria and organic foulants in the mixed liquor of membrane bioreactor. The study offers an effective way to enhance membrane anti-biofouling ability through the addition of antibacterial agent QAC. (C) 2016 Elsevier B.V. All rights reserved.