Denitrifying phosphorus accumulating organisms enrichment and their characteristics in a denitrifying enhanced biological phosphorus removal system

Denitrifying phosphorus accumulating organisms (DPAOs) play an important role in simultane-ous removal denitrifying nitrogen (N) and phosphorus (P). Their enrichment and characteristics were investigated. A denitrifying EBPR reactor, performing continuous anaerobic/anoxic conditions, was used to enrich DPAOs in this study. Through 60 days operation, DPAOs was successfully cultivated in the denitrifying EBPR system and P concentration in the effluent was stable and low with less than 0.5 mg/dm³. Energy dispersive spectroscopy (EDS) analysis showed that P content in anoxic end sludge gradually increased with enrichment operation, which accounted for 2.9, 4.7, 6.2, and 7.9 wt. % in sludge samples at day 0 (i.e., seed sludge), and days 20, 40 and 60, respectively. Based on the batch test, a significant positive correlation was found between COD consumption and P release in anaerobic conditions and between nitrogen removal and phosphorus uptake in anoxic conditions. Furthermore, in anaerobic conditions, the P release rate was 4.2 mg P/(g MLSSh) being higher than the P uptake rate (2.8 mg P/(g MLSS h)) in anoxic conditions. Despite this, total anaerobic P release (8.5 mg P/(g MLSS)) was lower than anoxic P uptake total amount (11.2 mg P/(g MLSS)), implying an excess P uptake in anoxic environment. One whole cycle displayed the obviously denitrifying simultaneous nitrogen and phosphorus removal with more than 95% removal efficiencies in the denitrifying EBPR system.