Nitrate Promotes Phosphorus Removal in the Anoxic–Aerobic Sequencing Batch Reactor with Starch as Sole Carbon Source

Abstract

A novel biological phosphorus removal in anoxic–aerobic sequencing batch reactor (SBR) using starch as carbon source had been found, but the role played by nitrate in this process was not clear yet. To reveal the effect of nitrate, two laboratory-scale SBRs operated in alternating anoxic–aerobic (R1) and alternating anaerobic–aerobic (R2) modes, respectively, were applied in this study. Results showed that phosphorus removal efficiency reached 78% and 77%, respectively, in R1 and R2. During anoxic stage in the R1, the accumulation of lactic acid was 16.66 mg/L, which was higher compared with 2.22 mg/L in the R2. While volatile fatty acid (VFA) was detected in the R2 with 20.44 mg/L, it indicated that there was more than one way for fermentation of starch in the two systems. Moreover, the production and consumption concentration of glycogen (74.29 mg/g volatile suspend solid (VSS) and 72.54 mg/g VSS) of the R1 was lower compared with 92.64 mg/g VSS and 105.75 mg/g VSS in the R2, respectively. It suggested that the internal carbon source of phosphorus absorption mainly derived from the decomposition of glycogen in the R2, and phosphorus uptake efficiency was related to the consumption of glycogen. The different bacterial community structure of the two systems was detected by high-throughput determination. Lactic acid-producing bacteria, such as Saccharibacteria genera incertae sedis and Enterobacter were predominated of the R1, whereas Thiothrix, Thermomonas, and Chryseolinea were dominant in the R2. It demonstrated that nitrate was more conducive to the enrichment of lactic acid-producing bacteria, thus promoting phosphorus uptake. This study improved our understanding of phosphorus removal by fermenting bacteria.