Comparative study on charcoal production by pyrolysis of fermented sludge with different inoculants

To investigate the effects of anaerobic fermentation with different inoculants on the pyrolysis behavior of biomass，this study used biogas residues from anaerobic digestion of corn straw inoculated with rumen fluid and sludge as examples. The pyrolysis characteristics of the materials before and after anaerobic fermentation were analyzed using thermogravimetric analysis and pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS)，and the resulting biochar was characterized. The results indicated that the apparent activation energy required for the pyrolysis of biogas residues was higher than that of the raw material before fermentation，indicating greater thermal stability. Furthermore，the activation energy required for the pyrolysis of sludge-fermented biogas residues was higher than that for rumen fluid-fermented biogas residues. The volatile products generated during pyrolysis were predominantly phenolic compounds and carbonyl compounds. The biochar yield from biogas residues was significantly higher than that of the raw material，exceeding 60% in both cases. Compared to the raw material，biochar from biogas residue showed increased surface roughness and porosity，resulting in higher specific surface area and porosity. Additionally，the biochar from sludge fermentation had a higher specific surface area and porosity than that from rumen fluid fermentation，though the relative content of pyrrolic-N was higher in the latter. This study provides a reference for the resource utilization of biogas residues.