Synergistic simultaneous nitrification-endogenous denitrification and EBPR for advanced nitrogen and phosphorus removal in constructed wetlands

Abstract This study assessed the feasibility of achieving phosphorus removal through enhanced biological phosphorus removal (EBPR) in an intermittent aeration constructed wetland (CW). The results showed that within just 3 weeks, a polyphosphate-accumulating organisms (PAOs)-enriched biofilm was successfully established in the CW by integrating a pre-anaerobic stage, intermittent aeration and periodic PO3-4-P release strategies. This strategy enabled a high PO3-4-P removal efficiency of 92.68% using normal gravel as a substrate. Moreover, simultaneous nitrification-endogenous denitrification (SNED) was found to be the main nitrogen removal pathway in the EBPR-CW without specific control. SNED significantly reduces the demand for oxygen and organic carbon compared with classical nitrification-denitrification, and allowed the system to reach 96.21% total nitrogen (TN) removal even under carbon limiting conditions. With control experiment, EBPR combined with SNED in CWs improved the phosphorus and nitrogen removal by about 73% and 48%, respectively, compared with normal nitrification-denitrification and media storage-based nitrogen and phosphorus removal processes. Based on stoichiometric analysis, 71.25% of PO3-4-P was removed by aerobic PAOs (APAOs), with 27.50% removed by DPAONi (denitrifying PAOs using nitrite as electron acceptor) and 1.25% removed by DPAONa (denitrifying PAOs using nitrate as electron acceptor). DGAOs were the main organisms providing nitrite to DPAOs. Overall, our results demonstrate a novel approach to combine SNED with EBPR for advanced nitrogen and phosphorus removal in CWs.