[Intensity of nitrification and denitrification in subsurface-flow constructed wetlands].

To reveal the nitrogen purification mechanism in subsurface-flow constructed wetlands, nitrification and denitrification intensities were studied in reed, canna and unplanted wetlands respectively. The results show that nitrification intensity in subsurface-flow wetlands is remarkably influenced by temperature and closely correlative with total and ammonia nitrogen removal efficiency. It appears in upright direction that nitrification and denitrification intensities in upper layer are higher than that in the lower. For the reed wetland, nitrification intensity is low in both ends but high in the middle of upper layer, while it decreases gradually along distance in lower layer. The change of denitrification intensity along distance is not obvious. Average nitrification intensity is higher in vertical-flow wetland than that in horizontal-flow wetlands, higher in planted wetlands than that in unplanted wetland and higher in reed wetland than that in canna wetland. The secretion from plant roots directly results in the gradual decrease of nitrification intensity in plant rhizosphere. Results also show that intensity of denitrification is obviously higher than that of nitrification. Thereby, subsurface-flow wetland has strong denitrification potential.