| The reuse of reclaimed water is an important measure to alleviate the shortage of water resources,ensure sustainable utilization of water resources,and promote the process of circulation society. But due to the limitations in economy and technique, reclaimed water contamination by nitrogen cannot be removed effectively. Unreasonable recharge or infiltration is likely to cause the pollution of groundwater and threat the security of water supply. The research on the effect of the transformation and biodegradation of nitrogen on groundwater during the reclaimed water infiltrating through the vadose zone media has a great significance for the reasonable utilization of renewable water resources and reduction of the contamination by nitrogen.Based on the project of using water resources from Wenyu River in Shunyi New City,and the column experiments indoors, this dissertation is dedicated to do column tests for simulation of the transformation and biodegradation of nitrogen during the infiltration of reclaimed water through the vadose zone media. Through making an analysis to the lithology characteristics of drilling sample taken from the allocation,the correlativity between the soil's physical and chemical indexes were discussed and the unsaturated zone's typical medium(sand-gravel, sand and silty clay) were identified.Then, this article used the typical mediums and the reclaimed water taken from the allocation as the column experiment materials and experimental water to conduct the simulative column experimental research of single medium and integrated medium. The analysis of the ammonia-nitrite-nitrates'consistency at different depth of experiment column shows the changing trends and gets the TN's variable rate constant and the NO3-N's denitrificaton rate constant, offering reliable parameters for the establishment of water modeling of diverting water resource from Wenyu river to Chaobai river. The results show that: (1) the four indicators of soil cation exchange capacity (CEC),total organic carbon(TOC),clay minerals content and clay content have no direct relationship with depth, but are closely related to the characteristics of the media themselves. Each correlation coefficient of two indicators is greater than 0.8 in significant level ofα= 0.01 .(2) The background values of TN in the sand-gravel and sand are all small, but silty clay's is relatively larger. The three media's background values of TN are 1.33,2.05,6.36 mg/100g; The three media's background values of nitrate-nitrogen are 1.46,1.82,10.15 mg/100g.The dissolution of TN in the three column experiments all meet the stability before 10-20 days.(3) Through the single medium column experiment, the variable rate constant of TN is: Kgravel = 1.667(m-1); Ksand = 1.682(m-1); Kclay =2.990(m-1). The denitrificaton rate constants of nitrate-nitrogen is Kgravel = 2.694 (m-1); Ksand = 3.738 (m-1); Kclay = 6.557 (m-1). And this shows that the efficiency of silty clay to remove nitrogen pollution is significantly higher than that of sand-gravel and sand.(4) Temperature plays an important role in the transformation and biodegradation of nitrogen. But when sand-gravel and sand are all but non-functional at a lower temperature, silty clay can still have some removal effect on the contaminants of nitrogen and have the same conclusion in the single medium column experiment. This makes out that silty clay also contributes greatly to reducing the nitrogen contaminants, and further deduces that the mechanism of removing nitrogen pollutants is not only based on adsorption and biological procession, but conceivably on other factors as well. |
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