For　weak　municipal　wastewater　(COD　＜=　200　mg　L-1,　NH4+-N　＜=　40　mg　L-1)　with　low　influent　C/N,　a　pilot　modified　four　step-feed　process　was　applied　for　simultaneous　biological　nitrogen　(N)　and　phosphorus　(P)　removal　under　different　inflow　distribution　ratios.　It　was　designed　with　a　short　hydraulic　retention　time　of　8.7　h　to　raise　influent　load,　and　the　optimal　effluent　performance　of　COD,　NH4+-N,　total　nitrogen　(TN)　and　total　phosphorus　(TP)　were　33.05,　0.58,　9.26　and　0.46　mg　L-1,　respectively　with　inflow　distribution　ratio　of　20:35:35:10%.　More　than　74%　of　carbon　sources　were　utilized　effectively　for　phosphorus　release　and　denitrification.　About　16.7%　of　TN　was　removed　through　simultaneous　nitrification　and　denitrification　in　oxic　zones.　Moreover,　the　commendable　sludge　settling　with　a　sludge　loading　of　0.04-0.1　kg　COD/kg　MLSS　d,　attributed　to　the　higher　mixed　liquor　suspended　solids　(MLSS)　and　the　alternating　anoxic/oxic　operational　mode.　In　addition,　the　pre-anoxic　zone　designed　was　beneficial　for　both　nitrate　reduction　and　anaerobic　phosphorus　release.　(C)　2012　Elsevier　Ltd.　All　rights　reserved.