Biological nutrient removal with limited organic matter using a novel anaerobic–anoxic/oxic multi-phased activated sludge process

An anaerobic–anoxic/oxic (A2/O) multi-phased biological process called ‘‘phased isolation tank step feed technology (PITSF)’’ was developed to force the oscillation of organic and nutrient concentrations in process reactors. PITSF can be operated safely with a limited carbon source in terms of low carbon requirements and aeration costs whereas NAR was achieved over 95% in the last aerobic zone through a combination of short HRT and low DO levels. PCR assay was used for XAB quantification to correlate XAB numbers with nutrient removal. PCR assays showed, high NAR was achieved at XAB population 5.2 · 108 cells/g MLVSS in response to complete and partial nitrification process. It was exhibited that low DO with short HRT promoted XAB growth. Abbreviations: PITSF, phased isolation tank step feed; A2/O, anaerobic–anoxic/oxic; SBR, sequence batch reactor; NAR, nitrite accumulation rate; SND, simultaneous nitrification and denitrification; MLVSS, mixed liquor volatile suspended solid; XAB, ammoniaoxidizing bacteria; XNOB, nitrite oxidize bacteria; XPAOs, phosphate accumulating organisms; XDPAOs, denitrifying phosphorus organisms; XH, heterotrophic organisms; PCR, poly chain reaction; PLC, programmable logic control; FISH, fluorescence in situ hybridization; SRT, sludge retention time; HRT, hydraulic retention time; COD, chemical oxygen demand; TP, total phosphorus; VFA, volatile fatty acids; TN, total nitrogen; NH4^+ -N, ammonia nitrogen; NO3^- - N, nitrate nitrogen; NO2^- - N, nitrite nitrogen; PHA, poly-hydroxylalkonates; DO, dissolved oxygen; OUR, oxygen uptake rate.