Coagulation-flocculation is a relatively simple technique that can be used successfully for the treatment of old leachate by poly-aluminum chloride (PAC). The main objectives of this study are to design the experiments, build models and optimize the operating parameters, dosage m and pH, using the central composite design and response surface method. Developed for chemical organic matter (COD) and turbidity responses, the quadratic polynomial model is suitable for prediction within the range of simulated variables as it showed that the optimum conditions were m of 5.55 g/L at pH 7.05, with a determination coefficient R² at 99.33%, 99.92% and adjusted R² at 98.85% and 99.86% for both COD and turbidity. We confirm that the initial pH and PAC dosage have significant effects on COD and turbidity removal. The experimental data and model predictions agreed well and the removal efficiency of COD, turbidity, Fe, Pb and Cu reached respectively 61%, 96.4%, 97.1%, 99% and 100%.

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Electrocoagulation has lately received much interest as an effective method for the treatment of landfill leachate because of its ease of use, low cost, and environmental friendliness. The present study aimed to investigate the reduction of chemical organic demand (COD), biological organic demand (BOD 5 ), and turbidity from leachate by electrocoagulation process using aluminium electrodes. In order to achieve the maximum removal of pollutants, highlight the key effects of the variables and their simultaneous relationships, full central composite design was applied. Moreover, the backward model selection method using Bayesian Information Criterion and Akaike Information Criterion was carried out to determine the most suitable model with relevant effects. The optimum conditions indicated by the estimated quadratic models were initial pH (5.04), current density (407 A m −2 ), reaction time (74.6 min), and stirring speed (150 rpm), adjusted R 2 of 99.82 %, 99.93 %, and 99.95 % for COD, BOD 5 , and turbidity, respectively. Electrocoagulation was also successful in achieving 90 % COD, 92.3 % BOD 5 , and 99.6 % turbidity removal efficiency. The findings indicated a satisfactory agreement between model forecasts and experimental values.

Coagulation/flocculation process was studied using the response surface methodology (RSM) and central composite design (CCD), to design the experiments, develop models, evaluate the relationship between operating factors (FeCl3 dose [m] and pH), and provide an efficient method for the treatment of old leachates. The quadratic polynomial models developed for chemical oxygen demand (COD) and turbidity responses indicated that the optimum conditions were m of 0.82 g/L at pH 5.33 with coefficient of determination R2 of 98.88 and 99.84%, and adjusted R2 of 98.09 and 99.73% for both COD and turbidity. The experimental data and model predictions agreed well. Chemical oxygen demand, turbidity, lead and copper removal efficiency of 76.4, 98.9, 99 and 99%, respectively, were reached.