Phenolic compounds adsorption from olive oil industry effluent using experimental design methodology: Screening and central composite design optimization

The experimental design methodology was investigated to model and optimize the adsorption process for removing phenolic compounds (PC) from olive mill wastewater (OMW) using magnesium-aluminum layered double hydroxide (LDH). The LDH powders were synthesized by the co-precipitation method. The structural, textural and morphological characterizations were performed. To evaluate quickly and effectively the effects of five parameters (initial PC content, contact time, solid/liquid (S/L) ratio, initial pH, and temperature) on the adsorption efficiency, a Hadamard matrix was employed for screening. Subsequently, a central composite design (CCD) was utilized to optimize the adsorption process based on four key parameters. The correlation coefficient for the polynomial model was found to be 94%. Predicted values generated from the response function matched the experimental data closely, indicating a good agreement. Under the selected optimal conditions, a maximum PC removal efficiency of 80.85 % was achieved. The reusability of the regenerated LDH by calcination at 500 °C in the adsorption process was assessed over four consecutive runs under the selected optimal conditions. The removal percentages of PC and chemical oxygen demand (COD) indicated that calcined LDH could be a viable alternative for treating OMW.