Application of response surface method for COD and TOC removal in leachate treatment through hybrid process (coagulation–flocculation/photo-Fenton/extended aeration)

In this study, the coagulation and flocculation (CF) process and photo-Fenton (PF) method have been used by examining the TOC and COD parameters in landfill leachate in Mallard, Iran. To optimize the studied parameters, the experimental design was performed in the design-expert software with the response surface method (RSM). At first, experiments related to the CF process were designed using the miscellaneous module, and then, the central composite module was used to experimental design in the PF process. The removal percentage of COD and TOC in the CF process using FeCl3 coagulant was obtained to be 30% and 63% at pH 11 and 100gL-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$100\mathrm{ g }{\mathrm{L}}^{-1}$$\end{document} of FeCl3 coagulant, respectively. Afterward, the output was used in the photo-Fenton process. The removal percentage of TOC and COD in the photo-Fenton phase (obtained at pH 7, 5 mgL-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{mg }{\mathrm{L}}^{-1}$$\end{document} of FeSO4.7H2O, 3.13 mgL-1\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathrm{mg }{\mathrm{L}}^{-1}$$\end{document} of H2O2, the reaction time of 62.5 min, and voltage of 14 V) was reported to be 34% and 68%, respectively. The correlation coefficients (R2) for fitted models in the CF process were equal to 0.9909 and 0.9261, respectively. In the PF process, the results were 0.9901 and 0.9883 proving the validity of the models presented. Finally extended aeration (EA) was also investigated to evaluate the effect of CF/PF processes which resulted in the 85% removal efficiency of the COD using the combination of CF/PF/EA processes. According to the obtained results, hybrid processes can be considered as an effective option in treating landfill waste leachate.