Treatment of Polluted River Water Using Biofilm Pretreatment and Sequencing Aerated Vertical Subsurface Flow Constructed Wetland

Polluted river water was the main source of the pollutants which import to the lake of Dianchi in China. A new treatment consisted of a low dissolved oxygen biofilm pretreatment and a sequencing aerated vertical subsurface flow constructed wetland was tested to treat the wastewater. Two other constructed wetland reactors were installed to compare and evaluate the efficiency of different aerated system and nitrification. The average removal rates of SS and COD in pretreatment were 88.7% and 58.6% when the DO in the reactor was between 0.2-1.5 mg/L, and the treatment performance was stably in different season. In the vertical subsurface flow constructed wetlands, loading rates of NH₃-N would reach up to 15 g/m²-d under the air/water ratio of 1:1 in sequencing aerated mode and which was more effective for DO increasing than the continuous aerated mode. TN removal efficiency was related by both nitrification and denitrification and the highest removal rate was 40.6%. The results showed that the use of biofilm pretreatment and sequencing aerated system reduced the risk of clogging and improved the nitrification significantly.