A2/O, anaerobic­anoxic/oxic; Biological nutrient removal; COD, chemical oxygen demand; DO, dissolved oxygen; FISH, fluorescence in situ hybridization; HRT, hydraulic retention time; MLVSS, mixed liquor volatile suspended solid; Microorganisms; NAR, nitrite accumulation rate; Nitrite accumulation rate (NAR); OUR, oxygen uptake rate; PCR assay; PCR, poly chain reaction; PHA, poly-hydroxyl-alkonates; PITSF; PITSF, phased isolation tank step feed; PLC, programmable logic control; SBR, sequence batch reactor; SND; SND, simultaneous nitrification and denitrification; SRT, sludge retention time; TN, total nitrogen; TP, total phosphorus; VFA, volatile fatty acids; XAB, ammonia-oxidizing bacteria; XDPAOs, denitrifying phosphorus organisms; XH, heterotrophic organisms; XNOB, nitrite oxidize bacteria; XPAOs, phosphate accumulating organisms; [Formula: see text], ammonia nitrogen; [Formula: see text], nitrate nitrogen; [Formula: see text], nitrite nitrogen