Experimental Design Optimization of Dairy Wastewater Ozonation Treatment

Abstract

In this work, an advanced oxidation process using ozonation combined with hydrogen peroxide (H2O2) and catalyzed by manganese (Mn2+) in alkaline conditions was investigated to degrade the organic matter present in a synthetic dairy wastewater (SDW) with a chemical oxygen demand (COD) of 2.3 g L−1. The effect of independent factors such as pH (7–13), H2O2/O3 ratio (0–1), and Mn2+ concentration (0–1.71 g L−1) has been evaluated and the process optimized using a factorial design and a central composite design (CCD) in sequence. The experiment has been made in batch trials using 2 L of SDW in which ozone was bubbled during 2 h and samples collected for COD analyses, used as response variable. In the factorial experiment, the effect of H2O2 was not significant for all the ratios tested (p value > 0.10), and the effects of the pH and Mn2+ were positive and significant (p value ≤ 0.05). In the CCD, the linear (positive) and quadratic (negative) effects of pH and Mn2+ were significant (p values ≤ 0.05 and ≤ 0.10, respectively). According to the response optimizer, the optimal condition for the ozonation catalyzed by manganese at alkaline medium (COD removal of 69.4%) can be obtained in pH 10.2 and Mn2+ concentration of 1.71 g L−1. Moreover, COD removals above 60% can be obtained for pH values of 9.5 to 11 and Mn2+ concentrations of 0.6 g L−1.