Improvement of Inflow Water Quality of Dian Lake Treated by Constructed Wetlands

Abstract

A surface-flow wetland and a subsurface-flow wetland respectively were constructed at the entrance of Dian Lake in Yunnan Province. Six plants such as Canna indica L., Scirpus tabernaemontanl Gmel., Eichornia crassipes (Mart.) Solms., Oenanthe ja vania (Bl.) DC., Acorus calamus L., Phragmitas communis Trin. were planted in the two constructed wetlands in separated sections on condition that hydraulic loading was 12 cm/d, hydraulic retention time (HRT) was 3 d. The results show that the removal efficiencies of subsurface constructed wetlands on TP and TN with canna indica L. or Scirpus tabernaemontanl Geml. are stable. Removal efficiencies of the former on TN and TP are 70.60% and 88.27%, respectively. Removal efficiencies of the later on TN and TP are 73.33% and 83.87%, respectively. Removal efficiencies of the constructed wetlands with Acorus calamus L. and Phragmitas communis Trin., the removal efficiencies of TN are 71.73% and 74.33%, respectively, and removal efficiencies of TP are unstable. The subsurface wetland of Eichornia ciassipes (Mart.) Solms. and Phragmitas communis Trin. on removal of TP and TN in summer or fall are more efficient. The two types of constructed wetlands have good effect on the removal of COD, which are above 78%, and the effluent concentration of CODcr is less than 57 mg/L .