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

[Display omitted] •Olive mill solid wastes were transformed into low-cost biochar by slow pyrolysis.•Biochar was used for the removal of polyphenols via batch adsorption.•Hydroxytyrosol appeared to have high adsorption affinity for the biochar.•Central composite design was applied to model polyphenols removal.•The adsorption percentage of hydroxytyrosol on biochar was greater than 92.5%. 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