This study evaluated the process characteristics of step feed 5-stage pilot plant (55㎥/d) in BNR(biological nutrient removal) process, such as the influent ratio, the effect of dPAOs(de-nitrifying phosphorus accumulating organisms) and temperature. In order to apply the microbial community in the process for operating and management as well as design, were using DAPI and FISH and 16s-rRNA for the pilot plant.
The maximum removal efficiencies of T-N and T-P were 80% and 83% when split ratio of Influent(Pre-ax : An : Ax-2 tank) was 1 : 6 : 3. The concentration of effluent were 8.0 mg/L-N and 0.7 mg/L-PO₄-P. As a result of step feed system operation, HRT was reduced mainly due to high concentration of MLSS, low yield, oxygen saved in oxic tank and high SNR.
In the investigation of temperature effect, nitrification-denitrification rate at 10 ℃was decreased to 1/3 and 1/4 based on the condition at 20 ℃. However phosphorous removal was independent of temperature resulting in 4.7 mgSP/L of removal potential. DPAOs fraction in PAOs was 55~70%(average 60%). Contribution of dPAOs for de-nitrification was 5-26% and for saved oxygen requirement was 0.5~4.3%. In the anoxic-1 tank, COD saving by dPAOs was 41% (2.4gCOD/gNO₃-N) for denitrification. Based on the result from temperature at 20 1C, specific phosphate uptake rate at 11-15 ℃ decreased in the oxic tank and the anoxic-1 tank, 76%, 30.5% respectively. DPAOs showed a greater temperature effect than that of PAOs for phosphate uptake.
From DAPI analysis, both in anoxic-1 and oxic stage, PAOs remained relatively high at 50% and 45%. From the dual staining comparison with FISH and 16s RNA, dominant groups that may be considered to be PAOs were high G+C gram positive bacteria group and Cytophaga-Flavobacterium group, the proportion was calculated from 15.8-18.8 % at minimum.