| Despite the success of water environment improvement and ecosystem restoration in recent years,the environmental degradation of surface water in China has been reduced,but solving the water pollution problem is still a daunting task.The high nutrient content in the tailwater of urban wastewater treatment plants has become a prominent problem facing the improvement of the surface water environment.Constructed wetlands can have a positive impact on ecosystems,promoting deep water purification and the restoration of aquatic ecosystems.When constructed wetlands are combined with wastewater treatment plants to achieve functional integration based on municipal wastewater treatment technologies,the construction of new wastewater treatment systems in constructed wetlands will further contribute to environmental protection and the sustainable development of aquatic ecosystems surface water.Constructed wetlands,as a deep treatment technology for wastewater treatment plant tailwater,currently face problems such as large footprint,low operating efficiency in low temperature environment,less than ideal denitrification effect and poor stability.Therefore,we need to improve and optimize it in order to better adapt to the actual operating environment and improve the treatment effect.This study optimizes wetland operation parameters by analyzing the pollutant removal effect of horizontal submerged wetlands and surface flow wetlands,the influence of hydraulic conditions and influent pollutant loads on them.At the same time the water quality of the wetland discharge is an important factor affecting the water quality of the recharged lake.The water quality and eutrophication of the lake were analyzed and the MIKE21 model was used to optimize the lake recharge scheme.The main conclusions obtained from this study are as follows:（1）The water quality target for the discharge water from the constructed wetland is Class IV standard for surface water environment.From March 2022 to February 2023,the attainment rates of COD,NH3-N and TP for the discharge water quality of submerged wetland were 100%,100%and 83.3%respectively The attainment rates of COD,NH3-N and TP for the discharge water quality of surface flow wetland were 100%,100%and91.7%respectively,and the monthly tailwater influent concentration has a certain influence on the water quality of the constructed wetland effluent.（2）The submerged wetland has a better COD removal rate than the surface flow wetland,and the opposite for NH3-N and TP.The mean values of COD,NH3-N and TP removal rate constants in the submerged wetland were all greater than those in the surface flow wetland.By controlling the water intake of each wetland,reducing the hydraulic load of the incoming water and extending the hydraulic residence time,the pollutant removal effectiveness of the wetland system is promoted to play out normally.Therefore,according to the specification and actual operation,the constructed wetland parameters were optimized as follows:horizontal submerged wetland hydraulic retention time of 1.0d,hydraulic load of 0.35 m3/（m2·d）and influent flow rate of 7000 m3/d.The surface flow wetland hydraulic retention time of 4.0 d,calculated hydraulic load of 0.1 m3/（m2·d）and influent flow rate of 3200 m3/d.（3）The water quality of the lake was analyzed for temporal and spatial variation characteristics from March 2022 to February 2023,and it was found that there were some differences in the water quality conditions of each indicator.The water quality target for the discharge of this constructed lake is the surface water environment class IV standard,and the compliance rate of DO,COD,NH3-N,TN and TP were 100%,91.6%,91.6%,0%and 83.3%respectively.In the nutrient-rich,sunny and slow-flowing environment,the lake waters were eutrophic throughout the year,except for November.（4）The MIKE21 model was used to construct a two-dimensional hydrodynamic-water quality model of the lake to study the effects of different recharge options on lake water quality.Compared with the existing recharge points,the option of adding recharge points 4 and 5 was most beneficial to improving lake water quality,and option 4 had the best effect on improving lake water quality,recharge points 1-5 had water volumes of0.13,0,0.23,0.1 and 0.23 m3/s respectively. |
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