Selected residual biomass valorization into pellets as a circular economy-supported end-of-waste

Abstract

Among prospective directions to convert residual biomass into valuable products is pelleting, which can be followed by low-temperature pyrolysis, serving as an economically justified method for reducing the final waste stream. In this study, fresh and biochar pellets were obtained from selected residual biomass – waste derived from widespread industries such as energy production, food processing, and forestry and chemical processing in a mixture with peat processing residues used as a binder. Obtained pellets consisted of woody biomass ashes (ASP3 and ASP5) or coffee grounds (CSP3 and CSP5) at equal proportions mixed with spruce needles biomass (48.5 % or 47.5 %) by adding 3 % or 5 % of peat processing residues as a binder, respectively, as indicated. Biochar pellets were obtained by pyrolyzing fresh pellets at 500 °C with a heating rate of 5 °C/min. Chemical-physical properties (e.g., moisture content, ash content, chemical composition, porosity, density) of pellets were studied. The most promising for further use were assessed CSP3. In turn, ASP5 were characterized by relatively higher carbon framework density, surface area (6.889  m²/g), and water absorption (97.83 %), indicating their use as a sorbent applicable, e.g., for wastewater treatment, while others can be used in soil quality improvement and sustainable agriculture support. The conversion of residual biomass into fresh and biochar pellets serves as an efficient approach in end-of-waste following the targets of circular economy towards zero-waste production.