Bioenergy production from olive oil mill solid wastes and their blends with lignite: thermal characterization, kinetics, thermodynamic analysis, and several scenarios for sustainable practices

Olive oil production is accompanied by the generation of large amount of solid wastes. In order to achieve a sustainable practice for olive mill solid wastes, the combustion of extracted olive pomace, olive stone, and their blends with lignite at different proportions was studied via several methods. Energy content, proximate, ultimate, and thermogravimetric/derivative thermogravimetric analysis (TG/DTG) were performed. Empirical chemical formulas and emission factors were calculated. Reaction kinetic parameters, such as activation energy (E), and pre-exponential factor (A) and thermodynamics parameters, such as Gibbs free energy change (ΔG α ), entropy change (ΔS α ), enthalpy change (ΔH α ), were calculated. Olive oil wastes reveal low ash (< 7%), high gross calorific value (GCV) (~ 21 MJ/kg), and lower activation energy (48.57 and 64.18 kJ/mol respectively) than lignite (70.79 kJ/mol). Maximum potential emissions were also lower. Furthermore, nine case studies with three different scenarios (%wastes into the blends) in three regions (Greece, Europe, and Worldwide) for the estimation of potential energy cover from olive oil solid wastes were developed. Quality characteristics of olive mill solid wastes seem to be appropriate to bioenergy for a sustainable practice. Even in the worst-case scenarios, olive mill solid wastes seem to be promising for waste-to-energy practices via combustion and co-combustion with lignite for small-scale applications. Graphical abstract