Modelling and Optimization of Coagulation–Flocculation Process of Landfill Leachate by Response Surface Methodology

Nowadays, due to the conventional methods of landfilling, the environmental concerns about generated leachate are becoming a global problem. Physical-chemical process is considered a potential and cost-effective solution for the treatment of municipal landfill leachate. Since jar-test are time-consuming experiments for obtaining the appropriate concentration of coagulants, the aim of this research was the treatment of landfill leachate using response surface methodology as a substitute for conventional methods in coagulation–flocculation process.

Experiments were performed in a six-cell jar-test with effective volume of 500 mL. The ability of Ferric chloride hexahydrate to response to four parameters including COD, TSS, alkalinity and turbidity was investigated. To evaluate the model and optimization of coagulant concentration and pH, central composite design and response surface methodology were used due to the highest removal efficiency. Physical and chemical analyses were performed based on standard methods for the examination of water and wastewater.

The results showed that the quadratic model was achived for the three responses (COD, TSS and alkalinity) and the Reduced Quadratic model was obtained for Turbidity under the optimum conditions for the concentration of 10.23g/L at pH 8.85. Verification experiments, under optimum conditions in removal of COD, TSS, turbidity and alkalinity resulted 66.79%, 88.61%, 97.53% and 67.89%, respectively. Statistical studies (ANOVA table, the amounts of R2 and P-value) showed that the models were suitable for providing experimental data and in all models, the R2 value was greater than 0.99. P-value values also showed that the effects of quadratic model and reduced quadratic model were significant in ferric choloride dosage and coagulation pH. These experimental results were consistent with those predicted by the model.

According to the obtained results by response surface methodology, coagulation–flocculation process can be used as the effective process to remove leachate inhibitors.