Multi-response optimisation of the solar photo-Fenton process for landfill leachate post-treatment

In this study, central composite design (CCD) and response surface methodology (RSM) were applied to assess and optimise the solar photo-Fenton process (Fe2+/H2O2 /solar UV) used as a post-treatment for a leachate from a landfill stabilisation lagoon system in Joao Pessoa, Brazil. Three variables were investigated: hydrogen peroxide (H2O2) factor, reagents ratio [H2O2]/[FeSO4] and initial pH of the reaction. The objectives were to maximise the removal of chemical oxygen demand (COD), turbidity and colour, and to minimise sludge generation in terms of settleable and total solids. According to the analysis of variance (ANOVA), all the response models using the selected variables were statistically significant, with determination coefficient (R-2) varying between 0.756 and 0.976. The optimal operational ranges were determined by overlaying contour plots: 0.83-1.50 (H2O2 factor), 3.70-5.40 (reagents ratio), and 2.72-3.15 (pH). The contour plots defined by the models showed strong interactions between the variables, whose values must meet the optimal ranges established in the study and follow these interactions to achieve COD removal > 75%, turbidity removal > 90%, colour removal > 97%, generation of settleable solids < 60 mL.L-1 and generation of total solids < 50 mg.L-1. The validation tests proved an excellent fit of the model to the experimental data. Finally, it was demonstrated that the solar photo-Fenton process was effective as a post-treatment for a mature landfill leachate, and its optimisation improved the quality of the final effluent.