Study On The Ammonium Transformation And Removal In Vadose Zone Under Different Environmental Conditions

Recently, ammonia has been one of the most popular pollutants in groundwaterin our country, especially in northern city. Ammonia is transformed to nitrite andnitrate by nitrifier. Nitrite and nitrate are uptaken by human and can induce manydiseases. Vadose zone is the necessary way for ammonia to enter the groundwater. Itis the important approach that ammonia pollution is controlled preferentially invadose zone to solve the for security problem of groundwater and soil. Ammonium insoil is not free and is adsorbed by mineral. Based on the different adsorptionmechanism, ammonium adsorbed is divided into different forms. This work proposeda novel method to eliminate the pollution of adsorbed ammonium in vadose zone. Inorder to investigate the factors influencing transformation and removal of differentforms of ammonium, the experimental media was obtained from the landfill inBeijing. The batch experiments of nitrification and denitrification were conducted byindigenous flora without the addition nutrients and acclimatization. The mainconclusions are as follows:(1)In the soil-water system, soluble and exchangeable ammonium could beutilized by ammonia oxidation bacteria, while less release of clay-fixed ammoniumwas observed under our experimental conditions.(2)The oxidation trends of soluble and exchangeable ammonium can be fittedby zero-order kinetics for different initial conditions. And soluble ammonium is moreeasily utilized than exchangeable ammonium in the same initial condition.(3)Under the different initial conditions, the ammonium transformations aremore sensitive to the change of soil moisture and initial concentration. The initialconcentration had a positive relation with the oxidation rate of ammonium. The soilmoisture had a strong effect on the lag period of ammonia oxidation.(4)The results in batch experiment for denitrification showed that it issuccessful to achieve the procedure of autotrophic denitrification and heterotrophicdenitrification by the addition of electron donor glucose and sulfide in theexperimental media. The heterotrophic denitrification rate increased from31.62%to60.53%with the increase of the C/N and also increased from47%to100%with theincrease of S/N ratio. During the heterotrophic denitrification, nitrite accumulated to 14mg/kg, while less accumulation of that was observed during the autotrophicdenitrification.