| Lake eutrophication caused by low-pollution water flowing into lakes has been one of the most important water environmental problems in the world.In view of the merits and demerits of low-pollution water treatment technologies,it is of great significance to reduce the eutrophication of lakes economically and effectively.In this paper,the low-polluted water of the river entering the north bank of Fuxian Lake was simulated to construct a composite constructed wetland,and the denitrification performance of the wetland was explored in combination with high-throughput sequencing.The optimized design was carried out based on the current situation of Xiaobaixiang wetland.The main conclusions are as follows:（1）Substrate selection.The results of isothermal adsorption and kinetic adsorption experiments show that Langmuir model fits well with the isothermal adsorption process of zeolite,ceramsite and volcanic rock.And the fitting effect of NH4+-N is better than that of TN.Ceramsite has the largest theoretical saturated adsorption capacity for NH4+-N and TN,and zeolite has the strongest adsorption capacity.Zeolite has the largest adsorption capacity for NH4+-N and TN.Considering the comprehensive results,zeolite and ceramsite were selected as the matrix of the system.（2）Screening of submerged plants.The nitrogen removal capacity of three submerged plants and their combinations were screened by static hydroponic experiments in laboratory.The results showed that the Ceratophyllum demersum L.had the best removal effect on NH4+-N.The combination of Myriophyllum spicatum L.and Hydrilla verticillata has the strongest ability to absorb NO3--N,TN and COD in water.The better purification effect of NO2--N was found in Hydrilla verticillata.In order to achieve the best treatment effect,different submerged plant ponds were constructed by selecting the combination of Myriophyllum spicatum L.,Hydrilla verticillate and Ceratophyllum demersum L..（3）Two different composite constructed wetland systems were constructed:（A）surface flow-horizontal subsurface flow-Ceratophyllum demersum L.,and（B）vertical-horizontal subsurface flow-Myriophyllum spicatum L.and Hydrilla verticillate.The denitrification effect of system A is better than that of system B under hydraulic load of 0.12 m~3/（m~2·d）.Under hydraulic loads of 0.16 and 0.24 m~3/（m~2·d）,system B is better than system A.During the test,the average removal rates of TN by A and B were 71.99%and 75.71%,respectively.And the stability of the B system was better.The removal of pollutants by different wetland units is different.NH4+-N is mainly removed in the first-level unit of the system while NO3--N is removed in the second-level unit of the system.NO2--N is accumulated in the first-level unit of the system A and removed in the third-level unit of the system B,NO2--N is accumulated in the first-level unit of the system B and removed in the second-level unit of the system.（4）The results of high-fluence sequencing showed that there were 13 main denitrification bacteria in the system,including Nitrospira,Saccharimonadales,Hyphomicrobium,Pseudomonas,Acinetobacter,etc.The dominant bacteria genera of different units are different.The microbial richness and diversity of submerged plants are better than that of substrates,and they have special denitrification function bacteria.（5）Optimization design of Xiaobaixiang wetland.In rainy season,back in operation,increasing the substrate and the submerged plant can improve COD removal rate（8.86%）,NH4+-N（12.35%）,TN（19.43%）,the effluent watwe quality close to the classⅢof surface water.In dry season the reflux operation,increasing the substrate and the submerged plant can improve COD removal rate（8.86%）,NH4+-N（12.35%）,TN（19.43%）,and the effluent quality close can reach the classⅢof surface water standard. |
