Engineering the physicochemical and energetic properties of biochar via conventional and microwave-assisted pyrolysis of softwood sawdust

A comparative study was conducted to assess the effect of pyrolysis temperature (300–600 °C) and heating variant (conventional and microwave-assisted) on the physicochemical and energy parameters of carbonaceous materials derived from softwood sawdust. Biochars were characterized in terms of basic technological parameters, such as moisture and ash content, elemental composition, type and amount of surface functional groups, pH value of the water extract, and thermal stability. Finally, the adsorption efficiency (including iodine number) and fuel-related properties (including higher heating value, HHV) were analyzed in relation to the applied pyrolysis pathway. It has been demonstrated that the pyrolysis method has a strong influence on the functional properties of materials derived from softwood sawdust pellets. Materials obtained via microwave-assisted conversion at 500–600 °C showed a 2–3 times higher iodine adsorption capacity compared to analogous biochars produced by conventional heating, which indicates an increased potential for removing low-molecular pollutants from the liquid phase. In contrast, biochars produced via conventional pyrolysis exhibited higher heating values (HHV) of 20–31 MJ/kg, indicating their suitability as solid renewable fuels. These findings demonstrate that the selection of pyrolysis conditions enables the targeted design of biochar materials with properties tailored to environmental remediation or energy applications.