Study On Denitrification Performance Of Enhanced Surface Flow Constructed Wetland With Plant Carbon Source

Plant Carbon Source was added to the surface flow constructed wetland（SFW）to enhance the denitrification nitrogen removal of the low C/N ratio agricultural runoff.Five pilot-scale SFWs were designed for experiment as follows: 0# the blank SFW（without plant carbon source）,1# SFW（areal proportion of Phragmites Australis pieces to enhanced denitrification wetland was 1/2）,2# SFW（areal proportion of Phragmites Australis pieces to enhanced denitrification wetland was 1/4）,3# SFW（areal proportion of Arundo donax pieces to enhanced denitrification wetland was 1/2）,4# SFW（areal proportion of Arundo donax pieces to enhanced denitrification wetland was 1/4）.A 243-day study was conducted to optimize the plant carbon source species Phragmites Australis and Arundo donax,plant carbon source dosing and operating depth.The main conclusions are as follows:（1）During the start-up period（1-40d）,plant carbon source（Phragmites Australis or Arundo donax）could shorten the start-up period and improve the removal rates of NO₃^--N and TN in the pilot-scale wetlands,and the wetlands which the areal proportion is 1/2 of plant carbon source was better than the wetlands which the areal proportion is 1/4.Phragmites Australis carbon source was better than Phragmites Australis in the early stage（1-18d）,but Arundo donax carbon source was better than Arundo donax in the latter stage（19-40d）.（2）The removal efficiency of NO₃^--N and TN in the pilot-scale SFWs was increased by adding the plant carbon source when the operating depth was 40 cm and the HRT was 3d in the pre-stage（61-91d）,the more plant carbon source was added and the better removal efficiency was.The removal rate of NO₃^--N and TN was reduced by adding Phragmites Australis carbon source in the post-stage（91-127d）,and the SFW which the areal proportion of Phragmites Australis carbon source is 1/2 was worse.The removal rate of NO₃^--N and TN was increased in 4# SFW which the areal proportion of Arundo donax carbon source is 1/4,but not in 3# SFW.The removal rate of NO₃^--N and TN in the blank SFW was 71.1%±0.5% and 71.0%±0.5%,respectively.The removal rate was the highest in 4# SFW which the areal proportion of Arundo donax carbon source is 1/4,it was 82.6%±1.0% and 78.6%±1.0%,and increased by 11.5%±1.0% and 7.6%±1.0%,respectively.The removal rate was the lowest in 1# SFW which the areal proportion of Phragmites Australis carbon source is 1/2,it was 65.9%±0.5% and 65.7%±0.5%,and decreased by 5.2%±0.5% and 5.3%±0.5%,respectively.The more plant carbon source was added and the better removal efficiency was in the pre-stage（61-91d）.The less plant carbon source was added and the better removal efficiency was in the post-stage（91-127d）,and Arundo donax carbon source was better than Phragmites Australis.（3）The removal efficiency of NO₃^--N and TN was reduced by adding the Phragmites Australis carbon source in the SFW which the areal proportion is 1/2 when the operating depth was 50 cm and the HRT was 3d in the stage（133-181d）.The removal efficiency of NO₃^--N and TN was increased in the stage（133-160d）in the SFW which the areal proportion of Arundo donax carbon source is 1/2,but it was reduced in the stage（160-181d）.The removal rate of NO₃^--N and TN in the blank SFW was 92.5%±1.0% and 90.9%±1.0%,respectively.The removal efficiency of NO₃^--N and TN was increased prominently in the SFW which the areal proportion of Phragmites Australis and Arundo donax carbon source is 1/4,and Arundo donax carbon source was better,the removal rate was 98.2% and 95.8%,and increased by 5.7%±1.0% and 4.9%±1.0%,respectively.The less plant carbon source was added and the better removal efficiency was in the stage（133-181d）,and Arundo donax carbon source was better than Phragmites Australis.（4）The removal efficiency of NO₃^--N and TN was reduced by adding the Phragmites Australis carbon source in the SFW which the areal proportion is 1/2 when the operating depth was 30 cm and the HRT was 3d in the stage（184-243d）.The removal efficiency of NO₃^--N and TN was increased slightly in the stage（209-243d）in the SFW which the areal proportion of Arundo donax carbon source is 1/2.The removal rate of NO₃^--N and TN in the blank SFW was 71.0%±0.5% and 63.3%±0.5%,respectively.The removal efficiency of NO₃^--N and TN was increased prominently in the SFWs which the areal proportion of Phragmites Australis or Arundo donax carbon source is 1/4 in the stage（209-243d）,and Arundo donax carbon source was better,the removal rate was 81.7%±0.5% and 77.2%±0.5%,and increased by 11.7%±0.5% and 13.9%±0.5%,respectively.The less plant carbon source was added and the better removal efficiency was,and Arundo donax carbon source was better than Phragmites Australis.（5）When the depth of SFWs was 50 cm and the areal proportion of Arundo donax carbon source was 1/4,the removal rate of NO₃^--N and TN was the best,and the removal rate was 98.2%±1.0% and 95.8%±1.0%,respectively.