Optimization of Coagulation-Flocculation Process for Mature Landfill Leachate Treatment Using Response Surface Methodology (RSM).

Coagulation-flocculation is a relatively simple physical-chemical technique in treatment of old and stabilized leachate which has been practiced using a variety of conventional coagulants. Polymeric forms of metal coagulants which are increasingly applied in water treatment are not well documented in landfill leachate treatment. In this research, capability of poly-aluminum chloride (PACl) in the treatment of stabilized leachate from Qazvin Landfill Site, Iran was studied. The removal efficiencies for chemical oxygen demand (COD), turbidity, color and total suspended solid (TSS) obtained using PACl were compared with those obtained using alum as a conventional coagulant. Central composite design (CCD) and response surface method (RSM) were applied to optimize the operating variables including coagulant dosage and pH. Quadratic models were developed for the four responses (COD, turbidity, color and TSS). The results of this study indicated that the optimum conditions were PACl dosage of 2 g/L at pH 7.5 and alum dosage of 9.5 g/L at pH 7. The experimental data and model predictions agreed well. COD, turbidity, color and TSS removal efficiencies of 39.95, 90, 87.9, and 87.3% for PACl, and 62, 78.8, 82.4, and 85.1% for alum were demonstrated. Results from this study showed that alum and PACl can be used as pretreatment of leachate for COD removal. Removal efficiency of PACl for turbidity, color and TSS is more than alum and alum usage is 5 times greater than PACl therefore it is concluded that PACl is better coagulant for enhancement of leachate characteristics than alum.