In　this　paper,　a　novel　submerged　ultrafiltration　(UF)　membrane　coagulation　bioreactor　(MCBR)　process　was　evaluated　for　drinking　water　treatment　at　a　hydraulic　retention　time　(HAT)　as　short　as　0.5　h.　The　MCBR　performed　well　not　only　in　the　elimination　of　particulates　and　microorganisms,　but　also　in　almost　complete　nitrification　and　phosphate　removal.　As　compared　to　membrane　bioreactor　(MBA),　MCBR　achieved　much　higher　removal　efficiencies　of　organic　matter　in　terms　of　total　organic　carbon　(TOC),　permanganate　index　(CODMn),　dissolved　organic　carbon　(DOC)　and　UV　absorbance　at　254　nm　(UV254),　as　well　as　corresponding　trihalomethanes　formation　potential　(THMFP)　and　haloacetic　acids　formation　potential　(HAAFP),　due　to　polyaluminium　chloride　(PACT)　coagulation　in　the　bioreactor.　However,　the　reduction　of　biodegradable　dissolved　organic　carbon　(BDOC)　and　assimilable　organic　carbon　(AOC)　by　MCBR　was　only　8.2%　and　10.1%　higher　than　that　by　MBR,　indicating　that:　biodegradable　organic　matter　(BOM)　was　mainly　removed　through　biodegradation.　On　the　other　hand,　the　trans-membrane　pressure　(TMP)　of　MCBR　developed　much　lower　than　that　of　MBR,　which　implies　that　coagulation　in　the　bioreactor　could　mitigate　membrane　fouling.　It　was　also　identified　that　the　removal　of　organic　matter　was　accomplished　through　the　combination　of　three　unit　effects:　rejection　by　UF,　biodegradation　by　microorganism　and　coagulation　by　PACT.　During　filtration　operation,　a　fouling　layer　was　formed　on　the　membranes　surface　of　both　MCBR　and　MBR,　which　functioned　as　a　second　membrane　for　further　separating　organic　matter.　(C)　2008　Elsevier　Ltd.　All　rights　reserved.