The　membrane　fouling　triggered　by　biofouling　layer　is　the　critical　factor　limiting　the　application　of　biofiltration-facilitated　gravity-driven　membrane　(GDM)　system　in　decentralized　drinking　water　treatment.　Powdered　acti-vated　carbon　(PAC)　and　alumina　(AA)　were　used　to　mitigate　membrane　fouling　by　pre-deposition.　Pre-deposited　PAC　and　AA　improved　the　stable　flux　of　the　biofiltration-facilitated　GDM　systems,　increasing　by　9.6%　and　17.0%,　respectively.　The　removal　of　dissolved　organic　carbon,　UV254　and　protein-like　material　was　sequentially　enhanced　by　pre-deposition　of　PAC　and　AA,　respectively.　Pre-deposited　AA　performed　better　than　pre-deposition　of　PAC　in　restricting　the　adhesion　of　soluble　microbial　products　to　the　membrane.　After　pre-deposition　of　PAC　and　AA,　the　porosities　of　the　biofouling　layers　increased　by　0.78%　and　2.51%,　and　the　protein/polysaccharide　ratio　in　extracellular　polymeric　substances　(EPS)　decreased　from　111.8%　to　53.4%　and　39.8%,　respectively.　The　protein　in　tightly　bound　EPS　showed　a　significant　positive　(p　＜　0.05)　relationship　with　the　total　membrane　resistance　and　genus　Acidovorax.　Zoogloea　was　the　core　genus　among　the　bacterial　communities　related　to　EPS　production.　Overall,　pre-deposition　of　PAC　and　AA　can　be　a　simple　and　effective　strategy　to　alleviate　membrane　fouling　in　biofiltration-facilitated　GDM.