Alternative approach for safe disposal of dry olive pomace: pyrolysis with/without physical preprocessing

Abstract

The aim of this study is to present an alternative approach for disposal by using pyrolysis for dry olive pomace (which is the leftover portion of raw olive pomace), which constitutes a problem in olive oil production facilities. In this context, dry olive pomace was pyrolyzed at 600 °C and two different pyrolysis durations: 5 °C/min heating rate without retention (total pyrolysis duration is 80 min) and 1 °C/min heating rate with 30-min retention after reaching target pyrolysis temperature (total pyrolysis duration is 550 min). Afterward, the effects of the dry olive pomace mixed with the olive mill wastewater and the pomace particle size during the pyrolysis process were evaluated in terms of pyrolysis product yields, inorganic contents of chars and organic fractions of bio-oil. While mixing of pomace within the wastewater resulted in an increase in the pyrolysis liquid, the effects of pomace particle size on pyrolysis product yields changed based on the pyrolysis conditions. A decrease in the particle size from 2 to 0.85 mm resulted in an increase in gas by 37.3% and a decrease in liquid by 37% at the pyrolysis process of 80 min. Furthermore, the decrease in the pomace size in grinding preprocess enhanced pyrolysis liquid quality in terms of a decrease in oxygenated compounds by 5–13% and an increase in aliphatic compounds by 7–20% at both pyrolysis durations. Consequently, dry olive pomace pyrolysis can be stated as one of the effective alternatives for safe disposal by converting waste into useful end products.