Application of response surface method for coagulation process in leachate treatment as pretreatment for Fenton process: Biodegradability improvement

Landfill leachate is a complex mixture containing toxic and recalcitrant substances with considerably low BOD5/COD indicating the necessity and difficulty of its treatment. Amongst treatment processes, integrated separating-destructive processes are promising ones. In this way, suspended and colloidal particles get separated in a separating process while the soluble fraction undergoes a destructive process; probably an advanced oxidation process. In the present study, coagulation process using ferric chloride was employed as a pre-treatment process for landfill leachate. Design of experiment, modeling and data analysis were conducted using response surface method (RSM) considering COD, color and TSS removals as responses. In optimum conditions (pH = 7 and 1500 mg/L FeCl3) the average COD, color and TSS removals were approximately 65%, 79% and 95%, respectively. Afterwards, Fenton process was applied for degradation of the leachate. Average oxidation state (AOS) and BOD5/COD values increased from −0.51 and 0.11 to +1.7 and 0.4 respectively. Phyto-toxicity test was also conducted based on the germination index which was dramatically increased after coagulation and Fenton processes.