Pretreatment Of Landfill Leachate In Lanzhou By Precipitation-oxidation Process

The change of modern city working style and the improvement of residents'living standard make the composition of household waste complicated and the output huge.At present,as a common waste treatment and disposal method,sanitary landfill inevitably produces leachate,which is characterized by high concentration,complex composition,unstable water quality and large water fluctuation,and random discharge will cause secondary pollution.As the leachate of lanzhou municipal solid waste landfill has high COD and ammonia nitrogen,pretreatment is required to provide conditions for subsequent treatment.Therefore,the combined treatment of chemical precipitation and Fenton oxidation is selected to reduce COD and ammonia nitrogen of the leachate.In this study,the precipitation-oxidation method combined with pretreatment of landfill leachate was studied in three stages.First,the single factor experiment of magnesium ammonium phosphate precipitation method and Fenton oxidation method was set respectively to determine the influence of the selected factors on the reaction.The factors and level selection were determined for the orthogonal experiment,and the optimal reaction conditions were finally obtained.The best reaction conditions and the removal rate of COD and ammonia nitrogen were explored by using the known results.?1?Experimental results show that in the stage of magnesium ammonium phosphate precipitation,the reaction should be carried out under basic conditions,and the appropriate pH=8-10.The removal rates of ammonia nitrogen and COD increased with the addition of magnesium ions and phosphate ions,and the reaction gradually reached equilibrium at[Mg²⁺]/[NH₄⁺]>0.8:1 or[PO₄^3-]/[NH₄⁺]>1.0:1.According to the orthogonal test,the influences of initial pH,magnesium and phosphate ion dosage on the reaction decrease successively,and the influences of initial pH on the reaction are huge.When pH=10,[Mg²⁺]/[NH₄⁺]=1.2:1,[PO₄^3-]/[NH₄⁺]=1.2:1,the removal rate of this reaction is the best.The optimal reaction conditions obtained by orthogonal experiment were used to obtain that the removal rate of ammonia nitrogen and COD increased with the increase of stirring time,and the removal rate increased slowly when the stirring time was 20 min.The removal rate of ammonia nitrogen and COD was 78.10%and 35.67%respectively at the optimal value of all conditions in this stage and the stirring time was 25 min.?2?In the Fenton oxidation process,the COD removal rate increases with the increase of hydrogen peroxide dosage,and it can be obtained that the dosage of hydrogen peroxide should be 6-10 ml/L,and the dosage of ferrous ion should be 4-8 g/L.Sufficient H⁺is required for the reaction,and the appropriate pH condition is 2-4.Orthogonal test results show that the effects of hydrogen peroxide dosage,ferrous chloride dosage and initial pH on the reaction decrease successively.When hydrogen peroxide is 10 ml/L,ferrous chloride is 6g/L,and pH=4,the reaction effect can reach the best.The best static time should be 120-180min;when the static time is 150 min,the removal rate of COD and ammonia nitrogen is64.9%and 13.48%respectively.The COD removal rate can be improved by adding hydrogen peroxide in 2-3 times.?3?For combined pretreatment,the reaction should be determined at pH=8-10.The removal rate of ammonia nitrogen and COD increased with the addition of magnesium ion and phosphate ion,and the removal rate increased slowly when[Mg²⁺]/[NH₄⁺]>0.8:1 or[PO₄^3-]/[NH₄⁺]>1.0:1.The effects of initial pH,magnesium ion dosage and phosphate ion dosage on the reaction were reduced successively by orthogonal test.When pH=10,[Mg²⁺]/[NH₄⁺]=1.2:1,[PO₄^3-]/[NH₄⁺]=1.2:1,the removal rate of this reaction can reach the optimal level.Under the optimal reaction conditions,the removal rate of ammonia nitrogen and COD increased with the increase of agitation time,which was 20 min.At this time,the removal rate of ammonia nitrogen was 78.9%,and that of COD was 77.8%.The experimental results of pretreatment of landfill leachate show that the combined sedimentation-oxidation treatment method has a good removal effect on COD and ammonia nitrogen in waste water and can provide conditions for subsequent treatment.