Study On The Pretreatment Of Landfill Leachate From Municiple Refuse

Sanitary landfill is the main process of the municipal refuse treatment, and it will produce landfill leachate that is very harmful for the environment. The landfill leachate is a complex wastewater with considerable variations in composition, and high concentration of COD,heavy metal ion and ammonia-nitrogen. Pollutant concentration of the landfill leachate used to change largely. If the landfill leachate is discharged into the environment, the soil and groundwater environment will be polluted severely. Currently, all of the processing craft in domestic and foreign are divided into three segments; the biological treatment is taken as the main body craft, the physical-chemical treatment and land method are taken as the pretreatment craft and the post-processing craft, respectively.The experiment mainly collected the refuse from residential areas, selected and filled, and then landfill leachate was be produced. Analyzed and contrasted the characteristic of the simulant leachate,based on the results of pre-experiment,deep research the pretreatment of COD and ammonia-nitrogen in landfill leachate with methods of Coagulation-chemical precipitation.By analyzed the water quality of the simulant leachate, the characteristic of variations in composition,high concentration of COD and ammonia- nitrogen was found from the simulant leachate, so we thought that this leachate would replace the practical leachate. And through the whole process of physical-chemical pretreatment, we found that the particle diameters of main contaminants were less than 1nm in this leachate.The paper studied two kinds of pretreatment methods, which were coagulation, chemical precipitation method. The experiment results showed that the optimum conditions of the coagulation were coagulant PFS, the pH value 7.0, doses 600mg/L, stirring rate 100rpm,the PAM doses 4mL/L, mixing time 20min, sedimentation time 45min.Under the optimum conditions, the removal rate of COD_cr was about 18%, the removal rate of ammonia-nitrogen was about 5%, respectively. But odors and ammonia- nitrogen of the leachate were not nearly removed.Using the function of magnesium ammonium phosphate to remove the ammonia- nitrogen from landfill leachate.The combination reagent was MgSO₄·7H₂O and Na₂HPO₄,the optimum pH was controlled about 9.5, the ratio of NH₄⁺:Mg²⁺:PO₄^3- was about 1.0:1.3:1.3, the reaction time was controlled 15min. The experiment results showed that the removal rate of ammonia-nitrogen reached 97.77%, but the COD_cr was not nearly removed. According to the results of the treatments, analyzed the technicality and economy of all of two pretreatments. Coagulation-chemical precipitation method (magnesium ammonium phosphate) was feasible as the pretreatment technology. And first, the coagulation should be used, then chemical precipitation method. The final result of the pretreatment showed that: the removal rate of COD_cr was 18.4%, the removal rates ammonia- nitrogen reached 93.7%. According to the results, we thought it reached the expectable purpose.