Production of bio-oil and biochar from digestate via pyrolysis in a mechanical fluidized bed reactor

The rising pressure to reduce greenhouse gas emissions calls for effective strategies to valorize organic waste streams. This study investigates the potential of slow pyrolysis to convert digestate, a byproduct of anaerobic digestion, into biochar and bio-oil using a mechanically stirred fluidized bed reactor. Experiments were done at 400, 450, 500, and 550 °C, with an additional run at 500 °C which employed a catalyst bed composed of process-derived biochar. As the temperature increased from 400 to 500 °C, the biochar yield decreased from 68 % to 50 %, while the bio-oil yield increased from 21 % to 30 %. The presence of the biochar bed further reduced biochar formation by approximately 5 %, enhancing vapor production. GC-MS analysis revealed that the bio-oil was primarily composed of carbonyl compounds, sterols, alcohols, and phenolic derivatives. These results demonstrate the influence of temperature and a biochar catalyst on product distribution and composition. Overall, the study supports pyrolysis as a viable pathway for digestate valorization and sustainable carbon recovery, contributing to emissions mitigation and improved resource management. • Digestate pyrolyzed in a mechanically fluidized bed reactor • Bio-oil yield rose from 29.8 to 31.7 wt% with biochar bed (+6.4 %) • Biochar bed improved gas recovery and enhanced H 2 (+58 %), reduced CO 2 (–20 %) • STAN analysis showed gas energy recovery rising from 23 % to 41 % • Energy recovery increased from 36.6 % to 47.7 % with catalyst (+30.3 %)