Study On Coagulation Pretreatment Of Landfill Leachate And Its Mechanism

Landfill leachate is a high intensity organic wastewater containing high concentration humic acid and salt,which has the characteristics of complex components,high content of COD and ammonia nitrogen,large fluctuation of wastwater quality and quantity,and laege pollution potential for the surrounding environment.The object of this research was the waste leachate liquid,the biochemical liquid and the concentrated liquid,which were taken from the landfill leachate treatment plant of Jiang Cun Gou in Xi'an.These three kinds of wastewater were treated by coagulation pretreatment processes,the best condition of coagulant and reaction condition was selected by comparing coagulants effects in different conditions.Finally,the main factors that influencing coagulation reaction were foud out by orthogonal test,and the coagulation mechanism of the main factors were analyzed.The research results would provided technical references for practical engineering.The main results of this study were as follows:?1?The experimental results of adding different coagulants such as aluminum chloride?AC?,ferric chloride?FC?,titanium tetrachloride?TiCl₄?,polyferric sulfate?PFS?and polyaluminum chloride?PAC?the samplet was completed after the reaction.The experimental results:the coagulant of PFS had better effect than other coagulants in landfill leachate,and the coagulant of TiCl₄ on landfill leachate biochemical and concentrated liquid were better effect than other coagulants.?2?When dealing with the waste leachate liquid,the optimal reaction conditions for the coagulant PFS:the dosage of PFS was 6g/L,the initial pH was 6,the temperature was30?,the mixing method:fast speed of 300r/min for 2min and slow speed of 50r/min for10mins,the dosage of PAM?1‰?was 1.5ml/L and sedimentation time was 30min.When dealing with the biochemical liquid,the optimal reaction conditions for the coagulant TiCl₄:the dosage of TiCl₄ was 4g/L,the initial pH was 7,the temperature was 30?,the mixing method:fast speed of 250r/min for 2min and slow speed of 50r/min for 10mins,the dosage of PAM?1‰?was 5ml/L and sedimentation time was 40min.When dealing with the concentrated liquid,the optimal reaction conditions for the coagulant TiCl₄:the dosage of TiCl₄ was 3g/L,the initial pH was 7,the temperature was 30?,the mixing method:fast speed of 300r/min for 2min and slow speed of 50r/min for 10mins,the dosage of PAM?1‰?was2ml/L and sedimentation time was 30min.?3?Within the established range of factors,the influence of various factors on the removal rates of COD,NH₃-N,SS and U_V254 can be seen from the magnitude of extreme differences.In the treatment of landfill leachate stock solution,the results of orthogonal experiments showed that the effect of COD treatment:mixing method>PFS dosage>temperature>initial pH>precipitation time,impact on the effect of NH₃-N treatment:PFS dosage>initial pH>temperature>mixing method>precipitation time,impact on the effect of SS treatment:mixing method>initial pH>temperature>precipitation time>PFS dosage,impact on the effect of UV₂₅₄ treatment:mixing method>temperature>PFS dosage>initial pH>precipitation time.?4?When dealing with the biochemical liquid of landfill leachate,the results of orthogonal experiments showed that the effect of COD treatment:TiCl₄ dosage>mixing method>temperature>initial pH>precipitation time,impact on the effect of NH₃-N treatment:TiCl₄ dosage>initial pH>temperature>precipitation time>mixing method,impact on the effect of SS treatment:mixing method>initial pH>TiCl₄ dosage>temperature>precipitation time,impact on the effect of UV₂₅₄ treatment:mixing method>initial pH>TiCl₄ dosage>precipitation time>temperature.?5?When dealing with the concentrated liquid of landfill leachate,the results of orthogonal experiments showed that the effect of COD treatment:mixing method>TiCl₄dosage>temperature>precipitation time>initial pH,impact on the effect of NH₃-N treatment:TiCl₄ dosage>initial pH>mixing method>temperature>precipitation time,impact on the effect of SS treatment:mixing method>TiCl₄ dosage>initial pH>temperature>precipitation time,impact on the effect of UV₂₅₄ treatment:TiCl₄ dosage>temperature>initial pH>mixing method>precipitation time.