Study On The Adsorption Mechanism And Removal Of Ammonium In Vadose Zone

With the development of society and the sharp increase of population, the pollution problem of ammonium in underground water is becoming more and more serious. Considering the harm of ammonium to groundwater and soil environments and human health, and the fact that there are no economic and effective remediation ways,this paper proposed a novel method to eliminate the potential menace of pollutant to groundwater by solving ammonium pollutant in vadose zone. Vadose zone media were taken from the refuse landfill in Beitiantang as the object of study in the experiments. And the research was carried on by the way of simulation pollution. By the changes of ammonium's characteristics in the tested media,internal and external factors affecting the adsorption of ammonium were discussed. Quantitative research of dynamics on ammonium's adsorption and liberation in the media were conducted as well. On this account, the effect of ammonium on the groundwater and soil environments was evaluated. With the experimental study of nitrification and denitrificaiton,each factor's conversion and ammonium removal was discussed, and therefore the possibility of ammonium in-situ remediation in vadose zone were subsequently discussed. The main conclusions are as follows:1) The deposit states of ammonium in the media have differences. Using the chemical form"Sequential Extraction Procedure"and combined spectral analysis and other methods, different forms of ammonium was depicted and characterized. The test results show that soluble ammonium adsorbs onto the surface of the media in the form of molecule and hydration ammonium. And desorption can occur under the effect of deionized water. Exchangeable ammonium results from exchange adsorption of ammonium ion and counterion Ca,Mg in the media. It can be completely desorbed by 1mol/LKCl. Fixed ammonium is the representation of ammonium ion fixed in expansible layers of minerals and it can only be released under the effect of 1mol/LHCl-5mol/LHF.2) The study of ammonium can be effectively used to conduct the quantitative analysis of ammonium's thermal dynamic process in the media. The test results show that each factor's influence on ammonium's adsorption in the media is expressed by the changes in the proportion of different forms of ammonium. Ammonium's adsorption dynamics in the media are controlled by ion exchange rate. The forms of the released ammonium on the media are mainly water soluble state and exchange state.3) Batch tests on nitrification show that the oxygen content is the most important condition for achieving nitrification. Oxygen content of less than 4% in the system will not completely inhibit the activity of nitrite-oxidizing bacteria. When the moisture content is over 13%, the ammonium of water soluble state and exchange state will be fully released and transformed. In solid phase,high concentration of ammonium has a certain restrain to the existence of nitrite-oxidizing bacteria. However , with the increase of nitrite-oxidizing bacteria's adaptability,the ammonium of water soluble state and exchange state will be fully released and transformed. Moreover,a large number of carbonate minerals in the media have an important influence on the accumulation of nitrite nitrogen in the system.4) The experimental study on denitrification shows that the media in the test can achieve the procedure of autotrophic denitrification and heterotrophic denitrification by the addition of electron donor glucose and sulfur element. Different types of electron donor lead to different degrees of nitrite nitrogen's deoxidation. In the tested media,S: N is higher than 30:1 and simultaneously can attain the 100% denitrification rate.