Research on the sewage purification effect of Multi-level composite constructed wetlands under low temperature in winter in Northern China- taking the Heituwa wetland of Guanting Reservoir as an Example

To address the challenges of overwinter operation for large artificial wetlands in Northern China,this study examines the Heituwa constructed wetlands of Guanting Reservoir using a “stable pond+ constructed wetland” combination process,investigating the water quality purification effects under low-temperature conditions from 2008 to 2020,while incorporating continuous inflow,operation under ice cover,and the maintenance of wetland macrophytes． Results indicate that water from the Yongding River meets Class III surface water standards after treatment by the Heituwa constructed wetlands． The removal rates for TN,NH₄⁺-N,BOD₅,TP,and orthophosphate are 30.84 %,60.14 %,36.84 %,39.47%,and 48.92%,respectively． The stabilization pond effectively degrades nitrogen and phosphorus nutrients,while the constructed wetland performs well in removing \mathrmNH_4^+ -N、COD_Mn and BOD₅.Different types of constructed wetlands have their own advantages,the purification effect of water quality in constructed wetlands as follows:subsurface flow wetland zone I> subsurface flow wetland zone IV > surface flow wetland.the removal rates for TN、\mathrmNO_3^- -N、TP in surface flow wetlands exceed those of subsurface flow wetlands by 5.64%,8.90%and 11.57%,respectively,while the removal rates in subsurface flow wetlands outperform surface flow wetlands for \mathrmNH_4^+ -N、COD_Mn and BOD₅ by 4.56%,13.67% and 12.27%． The removal efficiency of nitrogen elements in Zone I and Zone IV of subsurface flow wetlands tends to be consistent． The removal efficiency of COD_Mn and BOD₅ in zone IV are higher than zone I by 2.2% and 6.78%,respectively,while the removal efficiency of TP and orth-P in zone Iare higher than zone IV by 19.29% and 30.85%,respectively． The combination process of “stable pond+ constructed wetland” exhibits significantly high pollutant removal efficiency under low temperature in winter, providing a reference for the construction and operation management of wetlands in Northern China．