From food waste and its digestate to nitrogen self-doped char and methane-rich syngas: Evolution of pyrolysis products during autogenic pressure carbonization

Thermal conversion of solid digestate following anaerobic digestion (AD) can be a solution for producing value-added products and closing the material loop. The products of the novel autogenic pressure carbonization (APC) of food waste and two digestates were characterized to evaluate the temperature effect, product distribution and physicochemical composition. As the temperature increased from 300 to 700 ℃, char yields slightly decreased from 60.0% to 53.3% for the solid digestate from high-solid AD (SDH) while those of the solid digestate from low-solid AD (SDL) varied from 78.7% to 73.2%. X-ray photoelectron spectroscopy (XPS) results indicated that pyridinic N accounts for 40.0% of total N in char of SDL at 700 ℃ that can be upgraded to functional N-doped carbon materials. Maximum yield (39.8%) of syngas was obtained at 700 ℃ with SDH as a feedstock. After APC at 700 ℃, syngas, mainly consisted of CH4 and CO2, had heating values ranging from 22.4 to 24.6MJm－3, which can be jointly utilized with biogas from AD as fuel. Overall, results from this study demonstrate that APC could be used as a potential thermal conversion process for producing value-added products (N-doped biochar) and biofuel (syngas).