Novel Integrated Biorefinery for Olive Mill Waste Management : Utilization of Secondary Waste for Water Treatment

Olive mill waste (OMW) management has been a problem in the Mediterranean basin for thousands of years. The solid exiting the extraction process contains polyphenols that are beneficial to humans and phytotoxic to plants. We propose an integrated biorefinery concept for OMW management: supercritical fluid extraction to recover polyphenols, followed by pyrolysis of the solid to produce bio-renewable fuels, and finally activation of the biochar to yield high surface area adsorbents for heavy-metals removal from water. This work details the impact of supercritical fluid extraction on biochars that are subsequently activated with CO2 and KOH. Specific surface areas of the OMW biochars were over 2300 m2/g. Though supercritical fluid extraction increased the surface areas of raw, pyrolyzed, and KOH-activated OMW, the effect was reversed for biochars activated using high-temperature CO2. FTIR analysis showed that the supercritical fluid extraction significantly altered the surface functional groups of raw waste, but that activation conditions dictate surface characteristics of the resulting activated biochar. High-temperature KOH and low-temperature CO2 activation yielded activated biochars with the highest relative amounts of oxygenated functional groups. Activated samples demonstrate adsorption capacities upward of 400 mg of metal (Cd, Co, Cu, and Zn) per gram of sample and follow pseudo-second-order kinetics, with 75% adsorption capacity reached in less than 5 min. This integrated biorefinery concept simultaneously mitigates the environmental impacts of OMW disposal, yields high-value biopharmaceuticals and renewable energy, and provides a sorbent material for water treatment.