Study On The Transport Of Typical Pollutants In Tanning Sludge In Vadose Zone

With the rapid development of leather industry in China,serious environmental pollution problems were caused.Tannery sludge,as a solid waste produced in the tannery process,was often buried or stocked in the farmland without any contamination prevision measures.Due to the lack of environment supervision,The soluble pollutants in the sludge leach and infiltrate with precipitation,leading to the pollution of the aerated zone and even groundwater.In this paper,a tannery sludge dumping site was studied in Xinji City,Hebei Province.Based on the analysis of the basic properties of tannery sludge and the determination of characteristic pollutants,the pollution characteristics and distribution of chromium and ammonium in typical soil profiles of the study area were studied.At the same time,combined with indoor static and dynamic leaching experiments,the dissolution and release of ammonium in tannery sludge was studied.Secondly,the adsorption mechanism of trivalent chromium and ammonium by different media(silty soil and fine sand)was studied by adsorption experiment and one-dimensional soil column experiment.Moreover,the influence of Cr(III)on ammonium adsorption was analyzed.Finally,the basic parameters of soil column were obtained by tracer experiment.The Hydrus-1D model was used to simulate and predict the migration distance of ammonium in silty soil at different time intervals,and the potential pollution risk of ammonium release from sludge to vadose zone and groundwater was evaluated.1.The high content of ammonia nitrogen and chromium in the sludge has caused serious pollution to the shallow soil in the vadulation zone.The adsorption and precipitation of chromium in soil are obvious,and it is difficult to migrate downward.However,ammonia nitrogen migration is strong and environmental risk is high.2.The decrease of solid-liquid ratio,the increase of leaching time,the increase of temperature and the decrease of pH can all promote the release of ammonia nitrogen in sludge;The leaching experiment shows that the release rate of ammonia nitrogen is fast,an slow d the decline rate tends to be with the advance of time.3.The adsorption of ammonia nitrogen by silt and fine sand is mainly chemical adsorption,and the correlation coefficient between the isothermal adsorption curve of ammonia nitrogen and the Freundich model is high.Silt to Cr(Ⅲ)has strong ability of adsorption,the presence of Cr(Ⅲ)can reduce silt adsorption ability to ammonia nitrogen.4.The transport process of ammonia nitrogen in the vadose zone was affected by obvious adsorption,and the penetration curve showed obvious trailing phenomenon.Cr(Ⅲ)in powder soil column is hardly migration,migration in the Cr(Ⅲ)in fine sand column are greatly influenced by pH,the migration process is relatively slow.5.Without considering nitrification,hydrus-1d was used to simulate the migration process in the 45 m thick vadulation zone of the ammonia nitrogen research area.The results showed that it was difficult for low concentration of ammonia nitrogen to cause groundwater pollution through vadulation zone in a short time,while high concentration of ammonia nitrogen would cause groundwater ammonia nitrogen pollution in a long time.