Study On Landfill Leachate Treatment By Coagulation-MAP

High-concentration landfill leachate would be produced by the accumulation before the incineration of the domestic refuse.It has the characteristics of high COD and high ammonia nitrogen concentration,which makes it difficult to be treated by general biological treatment.For that reason,effective treatment for landfill leachate is a difficult problem,which has been widely studied at home and abroad.In this paper,coagulation+MAP precipitation has been used to deal with the landfill leachate produced in Weihai waste incineration plant.while the conventional coagulation and MAP precipitation have been optimized through the methods like composite coagulants,two-time coagulation and replacing agent with concentrated seawater.In addition,the effects that coagulant type,pH,coagulant dosage,dosage of composite coagulants and the dosage of coagulant in two-time coagulants would have on congulation,as well as the effects that the ratio of magnesium salt and phosphate,pH,reaction time,precipitation time,dosage of concentrated seawater,and impurity ions in seawater would have on the MAP precipitation have also been studied.The experiment result shows that two-time coagulation could be the best choice for the removal of turbidity and COD,when adding 4 g/L composite coagulant?PAC:PFS=2:1?at pH=9 with the stirring conditions of 300 r/min for 30 s,120 r/min for 60 s,40 r/min for 10 min,and then settling static for 10 min in the first coagulation and adding the coagulant of 0.5 g/L to the supernatant from the first coagulation,and the same stirring condition as that of the first coagulation in the second coagulation,after which the turbidity of the supernatant of the effluent would be 6.85 NTU.The highest removal rate of COD could reach to 54.29%when the dosage of coagulant changing to 8 g/L for the first time and 1 g/L for the second time.When concentrated seawater has been used as the source of Mg²⁺to remove ammonia nitrogen in landfill leachate,the optimum reaction parameters would be Mg²⁺:NH₄⁺:PO₄^3-=1.5:1:1.5,at room temperature,pH=9.1,stirring speed of 200 r/min,reaction for 15 minutes and precipitation for 10 minutes,after which the removal rate of ammonia nitrogen would be 67.61%and the residual concentration of PO₄^3-would be7.5 mg/L.Compared with the traditional MAP precipitation,the removal rate of ammonia nitrogen has been decreased by 1.28%.However,using seawater in coagulation could save economic cost and generate economic value.Though the method of two-time coagulation and MAP precipitation with concentrated seawater,the turbidity of the landfill leachate has been reduced from 1718 NTU to 3.5 NTU,the removal rate of COD has reached to 54.29%,and the removal rate of ammonia nitrogen has reached to 87.01%,which clearly shows the remarkable effect.