Effective treatment and the valorization of solid and liquid toxic discharges from olive oil industries, for sustainable and clean production of bio-coal

Abstract

Abstract Olive oil extraction processes generate significant quantities of wastes, olive mill solid waste, and olive mill wastewater, which are rich in precious compounds but toxic to the environment. In particular, olive mill wastewater is highly toxic. It is often discarded in water bodies without pre-treatment, causing severe problems for the aquatic environments. In this work, a new method was developed (based on high-temperature pyrolysis (500–950 °C)) to characterize and carbonize olive mill wastewater (25% weight of carbon) and olive mill solid waste (50% weight of carbon) with thermal shock (furnace pre-heated) under atmospheric pressure. Scanning electron microscopy, energy dispersive X-ray, Fourier-transform infrared spectroscopy, and X-ray diffraction techniques were used to properly characterize the produced bio-coal. The results proved the effectiveness of this pyrolysis technique. The solid and liquid wastes could be completely transformed into clean bio-coals, without the generation of by-products (pyrolysis oil or tar). The results showed that carbonization at 950 °C led to the production of porous and clean bio-coal (82% atomic of carbon) in 18% yield (compared to the initially treated mass). The optimal filling rate of the pyrolysis cell was approximately 30%. Moreover, the surface mass and the residence time influenced the yield of olive mill solid waste post carbonization. The optimal values were 210 mg/cm2 and 30 s, for a 51% yield of bio-coal relative to the initially treated mass. This carbonization process, according to the newly developed technique and the identified parameters, ensured a profitable, clean, and sustainable conversion and valorization of these wastes, in particular the olive mill wastewater.