Biochar from olive mill solid waste as an eco-friendly adsorbent for the removal of polyphenols from olive mill wastewater

Abstract

In Tunisia, olive mill waste water (OMW) is discharged into evaporation ponds where they turn into solid waste (OMSW) and become a serious threat to the environment. This paper addresses for the first time how to valorize OMSW into a biochar (BC) that can be used as an adsorbent aiming at either the recovery or the removal of polyphenols from the OMW. In this work, BC was produced through the pyrolysis of OMSW. Response Surface Methodology (RSM) approach was used for optimization of the process parameters. Analysis of variance revealed that all four parameters (pH, adsorbent dosage, pyrolysis temperature and polyphenols loading) had a significant effect on the adsorption (p<0.05). pH proved to be the most highly significant variable. The nonlinear Freundlich isotherm model was found to better describe the experimental adsorption process (R2=0.9911), while maximum polyphenol adsorption at 30°C was 140.47mg/g. Indeed, OMW is known as a source of natural antioxidant such as Hydroxytyrosol. In this work, hydrxytyrosol proved to have a high adsorption affinity for the BC. Therefore, adsorption using BC is an appropriate technique that maximizes the recuperation of hydroxytyrosol. After detoxification, OMW is invested for a variety of applications.