Landfill leachate pretreatment by coagulation-flocculation process using iron-based coagulants: Optimization by response surface methodology

Humic acids (HAs) are characterized as recalcitrant compounds in landfill leachate. In the present study, considering the HA removal as well as some traditional indexes such as chemical oxygen demand (CODCr), color and turbidity removals from landfill leachate, the performance of coagulation-flocculation (CF) process using iron-based coagulants was optimized by response surface methodology (RSM). The results achieved using polyferric sulfate (PFS) were compared with those using conventional coagulants such as ferric chloride 6-hydrate (FeCl3 center dot 6H(2)O), ferric sulfate 7-hydrate (Fe-2(SO4)(3)center dot 7H(2)O). The quadratic models developed for responses indicated the optimum conditions were PFS dose of 8 g/L at pH 6.0. FeCl3 center dot 6H(2)O dose of 10 g/L at pH 8.0 and Fe-2(SO4)(3)center dot 7H(2)O dose of 12 g/L at pH 7.5. Compromising to simultaneously optimize, the optimum conditions resulted in the CODCr, color, turbidity and HA removal of 56.38%, 63.38%, 89.79%, 70.41% for PFS whereas 68.65%, 93.31%, 98.85%, 80.18% for FeCl3 center dot 6H(2)O and 55.87%, 74.65%, 94.13%, 53.64% for Fe-2(SO4)(3)center dot 7H(2)O, respectively. The results of confirmatory experiments agreed well with the model predictions, which demonstrated that RSM can achieve good predictions with the least number of required experiments. Meanwhile, the relatively appreciable removals of HA and CODCr indicated that CF process as a pretreatment could remove recalcitrant compounds in leachate effectively. (C) 2012 Elsevier B.V. All rights reserved.