Study On Nitrogen Wipped Off From Polluted River Water By Gravel Riverbed

This paper associated with Demonstration project on techniques about water quality purification of plain river network and water body ecological restoration, which is supported by the National High Technology Research and Development Program of China (863 Program). This paper regards gravel contact oxidation method as the hardening purification technique for polluted river water bodies. The mechanism of wipping off nitrogen by gravel riverbed constructed by gravel contact oxidation method is studied. Wipping off nitrogen effects of gravel riverbed and nomal soil riverbed are compared, and the influence to wipping off nitrogen caused by hydraulic condition changes is also studied in this paper.The result of research shows that: (l)Be absorbed by gravel was the most important channel for the nitrogen be removed from water. The absorbtive amount took proportion 76.80% and 78.90% to the all removal amount in the initial phase, and these number changed to 50.51% and 52.11% at the end of experiment. Only 2.87—5.88% nitrogen was removed by ammonia volatilization. Denitrification effect of microorganism took proportion 19.20% and 18.05% to the all removal amount in the initial phase, and these number changed to 46.61% and 42.60% at last;(2)The nitrogen removal effect in gravel riverbed was evidently higher than which in normal soil riverbed at high velocity condition. At low velocity condition, the nitrogen removal effect in gravel riverbed was higher than which in normal soil riverbed at first 3-4 days, and then equal to or lower than which in normal soil riverbed. The appearance showed that the effect of adsorbing and entrapping nitrogen in gravel riverbed were better than which in normal soil riverbed. (3) Nitrogen removal effects were influenced evidently by the changes of hydraulic condition. TN removal effect were best at "high velocity and low depth" hydraulic condition. Nitrogen was wiped off more quickly at the higher velocity if the depths were same and the removal rate were higher at the lower depth if the velocities were same.