Effect of adding carbon source extracts on nitrogen removal in constructed wetland
补充碳源提取液对人工湿地脱氮作用的影响

To enhance the nitrogen removal efficiency in constructed wetland, Canna indica Typha latifolia and straw were hydrolyzed by dilute sulphuric acid under different conditions to get relevant carbon source extracts. Orthogonal test indicated that the increase of dilute acid concentration and time of the hydrolysis led to the increase of COD concentration. Straw hydrolyzed in 5% dilute sulphuric acid over 30 minutes had the highest COD concentration. The removal rate of nitrogen was high in the initial two days of the experiment. The removals of NH4+-N and TN obviously increased as the C/N ratio increased, while NH4+-N was controlled by DO and its removal was limited. Carbon source further restrained nitrification by competition for DO. Adding carbon source significantly enhanced the removal of TN and NO3--N, with the removal of TN increased from 54% to 95% and the removal of NO3--N increased from 48% to 96%.The accumulation of intermediate product, NO2--N, was dependent on the removal rate of NO3--N. When the removal of NO3--N was relatively high, no accumulation of NO2--N was found. Furthermore, denitrification in matrix showed an increasing tendency as the C/N ratio increased and denitrification in the fine sand layer was relatively higher than that in the rubble layer.