It　is　a　critical　challenge　for　drinking　water　production　when　treating　algae-contaminated　surface　water.　In　this　study,　the　impact　of　in　situ　coagulation　(C),　activated　alumina　filtration　(AA)　and　their　combination　(CAA)　on　the　performance　of　gravity-driven　membrane　(GDM)　was　systematically　assessed　during　105-day　operation.　The　results　indicated　that　pretreatments　in　particular　CAA　could　effectively　enhance　GDM　flux,　and　the　stable　fluxes　were　increased　to　3.1,　4.9　and　8.3　L/(m(2).h)　(LMH)　for　CGDM,　AA/GDM　and　CAA/GDM,　respectively　when　compared　to　the　control　GDM　(2.0　LMH).　Coagulation　was　beneficial　to　formation　of　thick　but　loose　biofouling　layer,　while　AA　filtration　was　effective　to　retain　foulants　including　extracellular　polymeric　substances　(EPS),　organics,　total　nitrogen　and　total　phosphorus.　The　CAA/GDM　could　mostly　remove　these　foulants,　and　facilitate　the　proliferation　of　bacterial　genera　that　could　consume　EPS,　further　alleviating　membrane　fouling.　The　dif-ference　in　loosely　bound　EPS　and　tightly　bound　EPS　of　biofouling　layer　attributed　to　the　difference　of　reversible　fouling　and　irreversible　fouling,　respectively.　Morphological　observations,　variation　in　functional　groups　or　el-ements　further　confirmed　the　difference　in　biological　layers　in　different　GDM　systems.　The　occurrence　of　specific　bacterial　genera　involving　the　potential　to　degrade　protein,　chitin　and　other　high　molecular　weight　organics　was　responsible　for　contaminant　removals.