Using central composite experimental design to optimize the degradation of black liquor by Fenton reagent

We investigated the advanced oxidation of the black liquor effluent from the pulp and paper industry using the dark Fenton reaction in a lab-scale experiment based on central composite experimental statistical design. The independent variables considered for the optimization of the oxidative process were temperature, H2O2 and Fe(II) concentrations, for a black liquor with a chemical oxygen demand (COD) of 628 mg·L−1 O2 at pH = 3. The response functions were the decrease in COD, aromatic content (UV254) and lignin content (UV280). The methodology lets us identify and statistically evaluate the effects and interactions of the study variables and their roles in the efficiency of the treatment process. In the optimization, the correlation coefficients for the model (R2) were 0.954 for COD, 0.936 for UV254 and 0.945 for UV280. Optimum reaction conditions at pH = 3 and temperature = 298 K were [H2O2] = 44.1 mM and [Fe(II)] = 4.655 mM. At these optimal conditions, the molar ratio H2O2/Fe(II) was 9.5. Under these conditions, 90 min of treatment resulted in a 94.8% decrease in COD, an 80.9% decrease in UV254 and an 85.6% decrease in UV280.

Research Highlights
► The oxidation of black liquor obtained from the pulping of wheat straw.
► Black liquor with high organic content: COD = 628 mg·L−1 O2.
► The central composite design was used to identify optimum Fenton reaction conditions.
► The optimum reaction conditions were: [H2O2] = 44.1 mM and Fe(II) = 4.655 mM.
► A 94.8% decrease in COD, 80.9% in UV254 and 85.6% in UV280 were obtained.