FeCl3 coagulation and dissolved air flotation (DAF) were combined to assess the success of these techniques for the treatment of semiaerobic landfill leachate. Treatment parameters (i.e.; flow rate, coagulant dosage, pH and injection time) were optimized via response surface methodology (RSM) using central composite design (CCD) to yield the maximum removal of turbidity, chemical oxygen demand (COD), color and ammonia nitrogen (NH3-N). Model-determined optimum conditions were tested to confirm the predicted results. Initial concentrations of turbidity (259 FAU), COD (2010 mg/L), color (4000 PtCo) and NH3-N (1975 mg/L) were reduced by 50%, 75%, 93% and 41%, respectively. These experimental results were consistent with those predicted by the model. The optimum operating conditions for coagulation and DAF were 599.22 mg/L of FeCl3 at pH 4.76 followed with saturator pressure of 600 kPa, flow rate 6 L/min and injection time of 101 s. (C) 2011 Elsevier B.V. All rights reserved.