Effects of COD/N ratio and SRT on the nitrifiers and PAOs

Abstract

This study focused on the relationship between reactor performance of BNR process, especially SBR, and microorganisms in the reactor. Because of their importance on wastewater treatment, nitrogen and phosphorus were concerned and the microorganisms on which treat these elements (nitrifiers and PAOs) were focused. On the other hand, COD/N ratio and SRT are very important parameters in wastewater treatment. Because COD/N ratio directly reflects the composition of wastewater and SRT is strongly related with sludge concentration. In this work, hence, SBRs with various COD/N ratios (5, 7.5, and 10) and SRTs (5, 30, and 60 days) were operated. Through all the experimental sets, better nitrification was achieved at longer SRTs and this trend showed good agreement with band profile of nitrifiers from DGGE. In FISH test, the same tendency was found out. Numbers of nitrifiers reacted to special probes that designed for the detection of nitrifiers were also more at higher SRTs. However, in case of COD/N ratio, nitrification was better than higher at lower COD/N ratio. Many kinds of and much amount of nitrifiers were also detected at this condition through DGGE and FISH respectively. Phosphorus removal efficiency was also high at longer SRTs. FISH results showed more PAOs at this condition as well. Moreover DGGE band had exactly same pattern to the reactor performance However, the effect of COD/N ratio on phosphorus removal was different. At low COD/N ratio, phosphorus removal efficiency was high in shorter SRTs but when it came to high, longer SRT reactors showed better removal efficiency. So to examine COD effect on phosphorus removal, one of batch tests was accomplished together with continuous experiment. The result indicated that COD has significant effect on phosphorus release especially at high sludge concentration. Finally one more batch test was conducted to find out the quantity of DNPAOs. From the slope of anoxic phosphorus uptake curve, it was revealed that DNP...