Attached microalgae-simulated plants enhanced multiple-pollutant removal in a tidal flow constructed wetland: quantified efficiencies, pathways, and biological mechanisms.

Active microalgae have great potential for releasing organic carbon and oxygen, which can be utilized as electron donors/acceptors, to enhance pollutant removal in constructed wetlands (CWs). In this study, we proposed a tidal flow CW with attached microalgae-simulated plants (AMSP) and verified the superiorities and mechanisms of microalgae's contribution to pollutant removal. The CWs with AMSP achieved high removal efficiencies for NH4N (87.6 %), TN (62.7 %), TP (56.4 %), and COD (98.8 %), which were 45.7 %, 16.3 %, and 20.5 % higher for NH4N, TN, and TP compared with those without AMSP. AMSP were found to enhance the abundance of functional microorganisms and genes involved in nitrogen metabolism, and to reduce the pH values in the bed filler to improve phosphate adsorption. Furthermore, the enhancement of NH4N and TP removal by AMSP was far beyond that of plants. Under the stress of 5 mg/L sulfamethazine (SMZ), the AMSP improved their photosynthetic efficiency and biomass accumulation, mitigated the impact of SMZ on the microbial community structure and diversity in the bed filler of CWs, increased the SMZ removal efficiency by 10.4 %, and reduced the release of antibiotics resistance genes into the environment by 49.7-89.6 %. These results demonstrated an effective integration of microalgal cultivation and CWs for treating wastewater containing emerging contaminants.