Migration And Transportation Of Ammonia In The Process Of River-bank Filtration In Dagu River Basin

During the process of contaminated river-water recharging groundwater, whether the groundwater will be polluted and the level of pollution depend on river-bank filtration system. As the main nitrogen pollutant in the water, ammonia is very hazardous to human being. Based on field investigation and sampling, the dissertation conducted batch experiments and column experiment to investigate the adsorption and transformation of ammonia using two filtration materials, sand and silt, which were collected from the riverbed of Dagu River. The results of the study could provide theoretical basis and technical support for controlling the potential pollution of groundwater in the process of contaminated river-water recharging aquifer.In the experiment of ammonia adsorption, the effect of temperature, pH and turbulence strength on the adsorption behavior of the two filtration materials was investigated. In the experiment of ammonia transformation, the effect of temperature and pH was investigated. In the simulation experiment, the hydrodynamic parameters and retardation coefficient of the filtration system was calculated and the actual behavior of transportation and transformation of ammonia in the simulated filtration system was investigated.The results of the dynamic adsorption experiment of ammonia indicated that the adsorption process of the two filtration materials could be divided into two stages, fast-adsorption stage and slow-adsorption stage. The adsorption rates of the two materials peaked at neutral pH. The equilibrium adsorption capacity of the two materials decreased with the increase of temperature. The adsorption rate of the silt reached maximum at 25℃, while the rate of the sand decreased with the increase of temperature. The adsorption rates of the two materials increase with the increase of turbulence strength. The results of the thermodynamic adsorption experiment showed that the adsorption isotherms of the two materials were both linear. The adsorption distribution coefficients of the two materials decreased as the temperature increased, but the equilibrium adsorption capacity of the two materials had little difference at low ammonia concentration. The adsorption distribution coefficient of the silt was one order of magnitude higher than that of the sand. The variation trends of the thermodynamic adsorption of the two materials were similar with the change of pH.The results of ammonia transformation experiment indicated that nitrification was the main process. As the temperature increased from 10℃ to 30℃, the nitrification rate also increased. The mathematical relationship between nitrification rate and temperature gained from the experiment was K=0.082×1.170T-2O(d-1). The nitrification rate of ammonia increased as pH increased from 6 to 8.The hydrodynamic parameters of the two materials were obtained by calculating the results of hydrodynamic dispersion experiment. The permeability coefficient, dispersion coefficient, dispersivity and effective porosity of the sand were 29.5 m/d,0.108 m2/d,4.05×10-3 m and 34.7%, respectively. And the above parameters of the silt were 0.471 m/d,7.10×10-3 m2/d,3.06×10-3m and 40.5%, respectively. The retardation coefficient on ammonia of the two materials were 2.47 and 8.36, respectively. The results of the simulation experiment indicated that the adsorption and nitrification of the silt and the adsorption of the sand were the main process during the removal of ammonia by the filtration system. A certain degree of denitrification could occur at low dissolved oxygen concentration. The capability of ammonia removal of the river-bank filtration system was limited.