An　experiment　was　conducted　in　a　membrane　bioreactor　(MBR)　to　investigate　the　start-up,　optimization,　and　membrane　fouling　behavior　of　a　simultaneous　nitritation,　anammox,　and　denitrification　(SNAD)　process　for　the　treatment　of　nitrogen-containing　organic　wastewater.　The　start-up　process　of　SNAD　included　three　periods:　first,　anammox　flocs　were　incubated　in　the　bioreactor　and　enriched　using　a　short　hydraulic　retention　time　(HRT)　from　24　h　to　4.0　h,　this　treatment　enhanced　the　anammox　start-up　process,　and　a　nitrogen　removal　efficiency　(NRE)　of　82.5%　and　nitrogen　removal　rate　(NRR)　of　0.49　kg/(m(3)d)　were　achieved.　Second,　a　completely　autotrophic　nitrogen　removal　over　nitrite　(CANON)　process　that　incorporated　aerobic　ammonium　oxidizing　bacteria　(AerAOB)　and　anaerobic　ammonium-oxidizing　bacteria　(AnAOB)　was　started　up　through　the　optimization　of　intermittent　aeration　(non-aeration　time　to　aeration　time　of　4.0:10　min),　in　this　process,　the　dissolved　oxygen　(DO)　remained　in　the　range　of　0.6-0.8　mg/L.　Third,　the　SNAD　process　was　started　up　by　introducing　organic　carbon　(sodium　acetate),　ammonium　removal　efficiency　(ARE)　of　91.2%,　NRE　of　77.9%,　and　chemical　oxygen　demand　(COD)　removal　efficiency　(CRE)　of　82.4%　were　achieved　at　a　C/N　ratio　of　0.5.　The　SNAD　process　was　further　optimized　by　regulating　the　C/N　ratio.　The　optimum　synergy　of　the　AnAOB,　AnAOB,　and　denitrifying　bacteria　(DNB)　was　achieved　at　a　C/N　ratio　of　1.0,　and　the　ARE,　NRE,　and　CRE　were　91.7%,　86.4%,　and　85%,　respectively.　A　SNAD　mass　balance　model　was　established　and　indicated　that　the　anammox　process　played　a　dominant　role　in　nitrogen　removal,　the　contribution　of　the　anammox　pathway　to　nitrogen　removal　was　64.7%.　The　membrane　fouling　rate　was　reduced　due　to　an　increase　in　the　particle　size　resulting　from　the　increase　in　the　extracellular　polymeric　substances　(EPS)　content　and　the　ratio　of　the　protein　to　carbohydrate　concentrations　in　the　EPS　(EPSp/EPSc).　Fourier　transform　infrared　spectroscopy　(FT-IR)　analysis　showed　that　protein　and　carbohydrates　were　the　main　components　of　the　membrane　foulants.　Moreover,　the　composition　of　the　membrane　foulants　exhibited　little　change　during　the　operation.