Treatment of olive mill wastewater by coagulation-flocculation and electro-Fenton processes: application of the experimental design methodology

The aim of this work was to evaluate the effect of combined coagulation-flocculation and electro-Fenton processes for the treatment of olive mill wastewater. Initially, pre-treatment by coagulation-flocculation was carried out using a full factorial design. The performance of coagulation-flocculation under conditions of [Aluminum Sulfate] = 3.33 g L(-)1, [cactus] = 11.3 g L(-)1, and pH = 5.0 resulted in 49.5 and 31.8% abatement of total polyphenols (TP) and chemical oxygen demand (COD), respectively. The pre-treated wastewater was then treated by the electro-Fenton process using a boron-doped diamond (BDD) anode in the presence of pyrite. A Box-Behnken design was successfully applied to determine the optimum treatment conditions: current = 0.3 A, pyrite = 0.3 g, pH = 3.5, and time = 60 min. Under these conditions, the abatement rates achieved for TP and COD were 54.9 and 72.8%, respectively. The energy consumption during the electro-Fenton process was relatively low, and a variance analysis (ANOVA) confirmed the statistical significance of the results. The combination of coagulation-flocculation and electro-Fenton processes significantly reduced the pollution load of organic compounds in olive mill wastewater, demonstrating the potential for an effective and energy-efficient treatment method.