Removal of COD, phenol, and colour from olive mill wastewater by iron-activated persulphate process: multivariate optimisation approach

Abstract

In this study, the treatability of olive mill wastewater by iron-activated persulphate (PS) oxidation was investigated. Central Composite Design (CCD) was applied to optimise the process parameters and establish a mathematical model for total phenol, chemical oxygen demand (COD), and colour removal from olive mill wastewater. The effect of process variables (PS dose, Fe2+ dose, initial pH, and reaction time) on pollutant removal efficiency was evaluated. The correlation coefficients of the quadratic polynomial equations were high for COD, total phenol, and colour removal by PS oxidation, and the model was found to be applicable. Optimum conditions determined by the developed model for maximum COD removal were pH 5, PS dose 206.7 mM, Fe2+ dose 70 mM, and reaction time 95 min. The COD, total phenol, and colour removal efficiencies estimated by the applied model were 46.74%, 94.62%, and 96.04%, respectively. The removal efficiencies obtained under optimum conditions as a result of the validation experiments were 45.5%, 93.8%, and 95.5% for COD, total phenol, and colour removal, respectively. The results of the study showed that PS oxidation in which Fe2+ is used as an activator is a suitable alternative for olive mill wastewater treatment.