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Abstract
Despite the fact that, in practice, enhanced biological phosphorus removal (EBPR) is often combined with biological nitrogen removal (BNR), the feasibility of nitrite (an intermediate in BNR) utilization, by denitrifying poly-P accumulating organisms (DPAO) is still unclear. In this study, the effect of nitrite on the EBPR was evaluated by investigating the dynamic response of DPAO to the gradual change of electron acceptor from nitrate to nitrite in an anaerobic/anoxic sequencing batch reactor (SBR). Under the nitrate condition, excellent EBPR was achieved, characterized by the DPAO biomass dominating in the sludge (51%–72% of VSS). Of the DPAO, 34% was the DPAOnitrate that could only use nitrate as electron acceptor, and 66% was the DPAOnitrite that could use nitrate/nitrite as electron acceptor. Nitrite in excess of 12 mg N/L had inhibition effect on the anoxic phosphorus uptake. As the electron acceptor changed, EBPR degraded slowly due to the gradual exclusion of the DPAOnitrate out of the reactor. The DPAOnitrite, therefore, became the single type of DPAO under the nitrite condition, and finally occupied only 33%–49% of the total sludge of VSS. Simultaneously, glycogen accumulating organisms (GAO), the competitor to the DPAO for substrate in the anaerobic phase, was significantly enhanced and grew to dominance in the reactor (46–62% of VSS). Also, the periodical exposure of sludge to the increased nitrite concentration elevated the inhibition level of nitrite for the anoxic phosphorus uptake (80 mg N/L). More attention should be paid to nitrite accumulation at full-scale wastewater treatment plants from the perspective of the stability of EBPR performance.
