Optimized hydraulic retention time for phosphorus and COD removal from synthetic domestic sewage with granules in a continuous-flow reactor

Abstract

In continuous-flow reactor (CFR), suboptimal hydraulic retention time (HRT) can affect the substrate loading, anaerobic time and aerobic time and further affect the performance and characteristics of granules, thus different HRTs (7.5, 6.0, 4.5 and 5.2h) were tested to improve the phosphorus (P) and carbon (COD) removal of the continuous-flow system with granules in this study. When HRT was below 6.0h, the COD removal efficiency in anaerobic zone and the P removal efficiency in aerobic zone reduced obviously, and the settling ability of EBPR granules deteriorated. The residual COD in anaerobic zone resulted in the proliferation of filamentous bacteria on the granules surface. Pyrosequencing analysis revealed that Proteobacteria was the dominant phylum in this system. The dominant class transformed from Betaproteobacteria to Gammaproteobacteria when HRT was reduced from 6.0h to 4.5h.