Biofouling　is　a　major　challenge　limiting　the　practical　application　of　biofiltration-facilitated　gravity-driven　membrane　(GDM)　systems　in　drinking　water　treatment.　In　this　study,　ultraviolet　irradiation,　including　ultraviolet　(UV)　and　vacuum　ultraviolet　(VUV)　irradiation,　was　used　for　in-situ　purification　of　membrane　tanks　to　control　membrane　biofouling.　After　using　UV　and　VUV,　the　permeate　flux　increased　significantly　by　26.1%　and　78.3%,　respectively,　which　was　mainly　due　to　the　decreased　cake　layer　resistance　(Rc).　The　permeability　of　the　biofouling　layer　improved　after　UV　and　VUV　application,　as　evidenced　by　the　increased　surface　porosity　and　decreased　thickness.　The　contents　of　loosely　bound　extracellular　proteins　(LB-PN)　and　tightly　bound　extracellular　proteins　(TB-PN)　in　the　biofouling　layer　were　reduced　after　UV　and　VUV　irradiation.　The　decreased　LB-PN　and　TB-PN　improved　the　interfacial　free　energy　between　the　fouling　itself　and　between　the　fouling　and　the　membrane,　which　contributed　to　the　reduction　of　interfacial　cohesion　and　adhesion,　resulting　in　a　looser　and　thinner　biofouling　layer　and　a　cleaner　membrane.　The　concentration　of　protein-like　material　in　the　membrane　tank　decreased　after　UV　and　VUV　irradiation,　significantly　altering　the　bacterial　community　structure　on　the　membrane　surface　(Mantel＇s　r　＞　0.7,　p　＜　0.05).　The　changes　in　the　metabolic　state　were　responsible　for　the　differences　in　the　LB-PN　and　TB-PN　contents.　The　inhibition　of　＂Alanine,　aspartate　and　glutamate　metabolism＂　and　＂Glycine,　serine　and　threonine　metabolism＂　reduced　amino　acid　biosynthesis,　which　restricted　the　secretion　of　LB-PN　and　TB-PN.　Critical　genera　in　the　Proteobacteria　phylum,　such　as　Hirschia,　Rhodobacter,　Nordella,　Candidatus_Berkiella,　and　Limnohabitans,　were　involved　in　metabolite　transformation.　Overall,　the　in-situ　application　of　UV　and　VUV　can　be　an　effective　alternative　strategy　to　mitigate　membrane　biofouling,　which　would　facilitate　the　practical　application　of　biofiltration-facilitated　GDM　systems　in　drinking　water　treatment.