Multiobjective Optimization of an Electroxidation Process of Biologically Pre-Treated Landifill Leachate by Response Surface Methodology and Desirability Function Approach

The optimization of the electrochemical step in a combined (biological and electro-oxidative) landfill leachate treatment was performed using a two stages approach, response surface methodology coupled with the desirability function. Four constraints were imposed, namely the discharge limit for COD (i.e. 160 mg / L), the maximization of color removal, the minimization of both residual chlorine and specific energy consumption. Each variable was modeled employing a second-order regression model. Analysis of variance (ANOVA) showed coefficient of determination (R2) values greater than 0.96, ensuring satisfactory fitting of the model output with the experimental data. After optimization at current density of 133 mA/cm2, stirring speed of 566 rpm and reaction time 46.2 min, the constrained COD removal percentage of 78.2% (corresponding to the aforementioned discharge limit) and a color removal maximization of 99.3% were observed. In addition, the minimization of residual chlorine and specific energy consumption reached the values of 1213 mg/L and 42.4 kWh/m3, respectively. The proposed methodology proved to be effective for saving time and experimental effort guaranteeing the achievement of optimal combination factors to reach specific target response. It is also noticeably that the overall operating treatment cost was lower than that presently found for sanitary landfill leachates. However, the high residual chlorine production leading to final effluent AOX concentration up to 35 mgCl-/L, represents an intrinsic treatment drawback. Keywords: Landfill leachate, electrooxidation, response surface methodology, desirability optimization methodology, COD removal, colour removal