Co-pyrolysis of plastics and agricultural waste: A strategy for designing biochars with fuel and adsorption potential

Biomass and plastic waste pose severe environmental challenges, contributing to soil, water, and air pollution. A promising circular economy approach involves converting these waste materials into reusable, carbon-rich products. In this study, biochars were produced via the pyrolysis of agricultural wastes from corn, tobacco, and tomato-biomass sources that are rarely employed for this purpose. To investigate improvements in physicochemical properties, co-pyrolysis was performed with high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), and their mixture (PsMix) at 10% and 50% weight ratios. The novelty of this work lies in the combined treatment of underexplored agricultural residues with mixed plastic waste streams, reflecting real industrial conditions where pre-sorting is uncommon. The methodology included systematic evaluation of carbon content and calorific values, alongside morphological characterization by SEM. The specific surface area and pore size distribution were assessed through the Brunauer-Emmett-Teller method. Results demonstrated that co-pyrolysis increased the carbon content up to ~70%. Some selected combinations, such as corn with 10% PsMix (32.7 MJ/kg) and tobacco with 10% HDPE (27.4 MJ/kg), reached levels comparable to coke. Moreover, co-pyrolysis significantly improved the specific surface area, with values up to 204.2 m²/g (tobacco + 10% PP) and 197.2 m²/g (tomato + 50% PS), suggesting suitability for medium- to high-performance adsorption applications. The results of these investigations showed that co-pyrolysis of agricultural and plastic waste produces biochar with fuel characteristics, but also with adsorption properties. In addition, the degradation of accumulated quantities of these types of waste contributes to sustainable solutions in the circular economy.