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Experiment on pretreatment of high strength landfill leachate with coagulation-flocculation

XING Hong 1,2, HU Xiao-min1, LIU Mei-ying1(1 School of Resource and Civil Engineering, Northeastern University, Shenyang 110004, China; 2 Department of Biological and Chemical Engineering, Liaoning Institute of Science and Technology, Benxi 117022, Liaoning, China)  
This paper aims to introduce the author's experiment with an optimum type coagulant and reactive conditions during the period of pre-treating high strength landfill leachate (COD_ Cr= 19 200~ 22 500 mg·L -1). The experimental leachate samples were collected at a landfill site near Shenyang. First we added lime dosages(5% calcium hydroxide) in the samples as a method to adjust pH. Next, we fed coagulant into the samples by stirring the sample at the same time for 5.0min. Then we put some PAM into the above samples. And, finally, calculate the COD_ Cr removing efficiency after sediment of the sample in 20min while watching the COD_ Cr of the upper water of the sample. In the process of adding the different coagulants into the same COD_ Cr samples in changing pH, the data of the removal COD_ Cr efficiency shows that the polyferric chloride coagulant which is made in our laboratory is the optimum coagulant to remove COD_ Cr under the condition of about pH 10.5. The experiment results show that the removing COD_ Cr efficiency has reached 64% under the optimum conditions: the adding coagulant rate 1 000∶3, pH being about 10.5, slowly stirring time being about 5.0 min, and the sedimentation time being 20 min. Landfill leachate, although small in volume, is extremely high in pollution capacity. The effect of leachate on groundwater can be severe. In addition, the coagulation-flocculation method can be used as a preliminary process in the treatment of landfill leachate. During coagulation the chemical reactions that take place in rapid mixing form precipitates. Flocculation is a contacting process which may bring the precipitates into contact with one another so that they can agglomerate and form larger particles. Thus, it can be concluded that the pretreatment of high strength COD_ Cr landfill leachate with the polyferric chloride proves to be favorable for heightening the COD_ Cr removing efficiency and preventing excessive loads on the next biological-treatment process.
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