Nutrient removal and phosphorus recovery performance of an anaerobic side-stream extraction based enhanced biological phosphorus removal subjected to low dissolved oxygen

Abstract

An enhanced biological phosphorus removal (EBPR) system based on anaerobic side-stream phosphorus recovery was operated to investigate the nutrient removal performance of the mainstream system under low dissolved oxygen (DO = 1.0, 0.6, 0.2 mg L−1) and the corresponding phosphorus recovery efficiency with different extracting ratio (m = 0, 1/4, 1/3, 1/2) of anaerobic supernatant within 310 days. The results showed that the nutrient removal efficiency remained stable even though DO was extremely low. Nevertheless, phosphorus removal performance was found to deteriorate as side-stream ratio increased to 1/3 at DO = 0.2 mg L−1, suggesting that extracting a higher ratio of supernatant was not favorable for phosphorus removal in the mainstream process at ultra-low DO. The stoichiometric ratios of Prelease/HAcuptake during anaerobic phase which decreased from 0.125 to 0.020 P-mol/C-mol as DO decreased with increasing side-stream ratio were lower than that of typical PAO metabolism. It was very likely that the metabolic mode of PAOs changed due to long-term deprivation of phosphate. Consequently, the mainstream EBPR system failed to remove phosphorus efficiently. It was also observed that phosphorus recovery efficiency was considerable at DO ≥ 0.6 mg L−1 coupled with high side-stream ratio. Therefore, it was feasible and energy-saving to extract appropriate ratio of anaerobic supernatant for recovering phosphorus and removing nutrient efficiently in an EBPR process under low DO.