A comparative study on thermochemical conversion behavior in biochar production through isothermal pyrolysis of cattle manure and sawdust.

Cattle manure is an ash-rich, compositionally heterogeneous organic-inorganic feedstock, whereas sawdust is a low-ash lignocellulosic material. Because these contrasting matrices may respond differently to pyrolysis, this study compares their thermochemical conversion behavior for biochar production under identical conditions (300-450 °C, 15-45 min). Organic conversion was evaluated by ash-normalized mass loss, and the resulting solid products, referred to as biochars, were characterized by proximate, elemental analyses, FT-IR, Py-GC/MS, and XPS. Cattle manure exhibited a slower and less extensive conversion of its organic fraction than sawdust. Gas evolution from cattle manure occurred over a broader temperature range, whereas sawdust underwent most devolatilization within a relatively narrow temperature window. These differences were consistently reflected in the properties of the resulting chars. Cattle manure showed smaller changes in proximate and elemental composition, shorter Van Krevelen trajectories, and greater retention of O- and N-containing functionalities in the solid phase. In contrast, sawdust chars exhibited more pronounced deoxygenation and carbon enrichment under the same conditions. Therefore, these observations suggest that the ash-rich organic-inorganic matrix and retained nitrogen-containing structures in cattle manure were associated with less extensive deoxygenation and carbonization under the isothermal temperature-time conditions, exhibiting the distinct pyrolysis behavior compared to sawdust.