Study of olive mill wastewater adsorption onto biochar as a pretreatment option within a fully integrated process

Abstract

The aim of the present study is to investigate the adsorption of dissolved organic matter in olive mill wastewater (OMW) onto biochar as a pretreatment step within an eco-friendly OMW management process. Firstly, the adsorption kinetics and adsorption isotherm were studied. Then, an experimental design was used in a sequential approach in order to evaluate the effects of factors that potentially influence the adsorption efficiency. Results showed that the OMW adsorption kinetics were governed by a pseudo-first-order model, while Freundlich and Redlich–Peterson models described the isotherm data well. It was also demonstrated that linear fitting is a limited method when applied to kinetics and isotherm modeling. Alternatively, nonlinear fitting is recommended for the appropriate modeling of adsorption data. Experimental design results showed that the organic matter removal percentage and biochar uptake capacity were oppositely sensitive to OMW concentration and biochar mass. Organic matter removal reached a maximum value of 28% for the highest biochar mass and the lowest OMW concentration, while biochar adsorption capacity attained an optimal value of 140 mg g−1 for the lowest biochar mass and the highest OMW concentration. These results show that adsorption is an effective pretreatment for OMW, albeit with quite limited efficiency. Adsorption can be performed in continuous mode using a cascade of adsorption columns or batches to further improve the removal efficiency.