A coagulation flocculation process combined with a Steel Industry Wastewater rich in ferric chloride (SIWW) and polymer were used to treat fresh leachate from municipal solid waste of the city Mohammedia. A central composite experimental design and response surface methodology were employed to evaluate and optimize the reagents dosage and to achieve a balance between efficiency and operational costs. The influence of pH was also evaluated to determine the most suitable pH condition. The best regression coefficients (R2) were obtained for phenol removal, colour removal and decanted sludge, with values of 0.89, 0.93 and 0.92 respectively. The most significant factors in the analysis of variance (ANOVA) in this study were pH and SIWW dosage. However, flocculant dosage was not most significant factor. Multiple response optimizations fits the optimum values of the factors and the responses as 40 mL.L-1 of coagulant, 12 mL.L-1 of polymer and 91% of phenol removal, 70% of colour removal and 38 mL.L-1 of decanted sludge at pH=6
