A　bench-scale　biological　nitrogen　and　phosphorus　removal　membrane　bioreactor　(UCT-MBR)　process　was　operated　to　treat　carbon-limited　municipal　wastewater　regarding　on　the　influences　of　ferric　chloride　(FeCl3·6H2O)　addition　on　the　process　performance　and　membrane　fouling.　FT-IR　(Fourier　translation　infrared　spectroscopy,　FT-IR)　and　EDX　(energy　dispersive　X-Ray,　EDX)　were　used　to　analyze　membrane　surface　foulants.　The　results　show　that　the　phosphorus　removal　is　strengthened　with　the　addition　of　ferric　chloride.　The　highest　removal　efficiency　of　TP　(total　phosphorus,　TP)　can　be　obtained　in　UCT-MBR　process　under　the　condition　of　the　optimal-phosphorus-removal　dosing　(dosage　of　1.8　mmol/L)　combined　with　the　biological　phosphorus　removal　process.　Membrane　fouling　is　alleviated　with　the　addition　of　ferric　chloride　mainly　through　increasing　the　sludge　particle　size　and　reducing　the　SMP　(soluble　microbial　products,　SMP)　fraction　concentration　with　relative　molecular　mass　above　105.　The　lowest　membrane　fouling　rate　in　the　UCT-MBR　process　can　be　obtained　under　the　condition　of　the　optimal-sludge-filterability　dosing　(dosage　of　2.6　mmol/L),　while　the　optimal-sludge-filterability　dosing　exhibits　a　strong　influence　on　sludge　bioactivities　and　reduces　the　sludge　capabilities　of　nitrification　and　phosphorus　release/uptake,　which　limits　the　performance　of　nitrogen　and　phosphorus　removal.　The　ferric　chloride　addition　has　no　effects　on　their　compositions.　Moreover,　the　influence　of　inorganic　fouling　on　membrane　fouling　rate　is　found　to　be　smaller　than　that　of　organic　fouling.　Besides,　lag　effects　are　found　for　inorganic　elements　combined　with　biopolymers　to　form　a　dense　cake　layer.　©　2016,　Central　South　University　of　Technology.　All　right　reserved.