Evaluation of biochar and hydrocar energy potential derived from olive mills waste: The case of Montenegro

Three different waste streams from olive oil production from Montenegro are utilized energetically by hydrothermal carbonization (HTC - hydrochar) and pyrolysis (biochar). Pyrolysis experiments of three-phase olive mill solid waste (3POMSW) were conducted for different pyrolysis temperatures of 450, 550, and 700 degrees C and a residence of 60 min for each experiment. HTC experiments for two-phase olive mill waste (2POMW) and a mixture of olive mill wastewater (3POMWW) and 3POMSW were carried out at 180, 200, and 220 degrees C, autogenous pressure of (1, 1.6, and 2.3 MPa) for 60 min. Increasing reaction temperature led throughout all experiments to a lower carbon recovery. Furthermore, all hydrochar and biochar samples had energy densification of more than one, indicating a higher mass-energy density than the initial feedstock. The highest energy yields were achieved for the 3POMW, with 46.48 % in hydrochar treated at 180 degrees C and 44.09 % in biochar treated at 450 degrees C. Concerning the hydrochar from 2POMW, the highest energy and mass yields of 62.53 % and 49.65 %, respectively obtained at 180 degrees C. Summarizing, the energy potential of Montenegro's olive mill waste (OMW) was estimated at 43.69 PJ, which roughly could cover the whole energy demand of the olive oil industry in Montenegro.