Abstract: Renewable energy is ever ever-increasing demand for the recycling of biomass wastes. This study aimed to explore the kinetics and potential energy of the agricultural and forestry waste, as well as their fermentation products during pyrolysis. Three types of the biomass wastes—corncob, leaves, and Auricularia dregs—were selected as the raw materials. Their fermented counterparts were prepared for the comparative analysis. Thermogravimetric analysis (TGA) and kinetic studies were conducted to investigate the pyrolysis behavior for the key thermodynamic parameters, including activation energy (E) and pre-exponential factor (A). Additionally, X-ray diffraction (XRD) was employed to analyze the crystal structure and phase composition of the samples. TGA results revealed that there was the a similar pyrolysis of the three materials and their fermentation products. Four weight-loss stages were divided in the pyrolysis. The first stage (30–120 °C) was corresponded to the evaporation of moisture, while the second stage (120–250 °C) was attributed to the decomposition of hemicellulose. The third stage (250–520 °C), the primary weight-loss phase, was associated with the pyrolysis of the cellulose and lignin. The final stage (520–800 °C) was involved the further decomposition of the residual char. Among the samples, the fermented leaves exhibited the lowest activation energy (2.66 kJ/mol), indicating a lower energy barrier for the pyrolysis reaction and higher potential for energy conversion. In contrast, there were the more complex pyrolysis products of the fermented corncob and Auricularia dregs. XRD analysis demonstrated that all samples shared a crystalline structure, with the SiO₂ was identified as the predominant phase. The fermented leaves and Auricularia dregs showed the similar peak positions, indicating the comparable crystal structures. While the fermented corncob exhibited the distinct diffraction patterns. The variations in crystal structure were attributed to the microbial degradation of cellulose, hemicellulose, and lignin during fermentation, which was altered the crystallinity and phase composition of the biomass. Therefore, the fermented leaves were highlighted to serve as a promising feedstock for biomass energy and chemical industries, due to their low activation energy and high conversion efficiency. In contrast, the more complex products were yielded in the pyrolysis of the fermented corncob and Auricularia dregs. A theoretical foundation was provided to understand the pyrolysis kinetics of the biomass waste. The practical guidance was offered for its efficient utilization. The agricultural and forestry waste was transformed into the valuable energy resources. This research was greatly contributed to the sustainable development of economic and ecological fields. In conclusion, the biomass waste can be expected to serve as a renewable energy source. The thermogravimetric analysis, kinetic modeling, and XRD characterization can be integrated to evaluate the pyrolysis behavior and crystal structure of the biomass materials. The fermented leaves can also serve as a high-efficiency feedstock. While the need can also be identified for the further exploration of biomass types. Additionally, the pyrolysis conditions can be optimized to maximize the energy yield for the minimum environmental impact, in order to significantly enhance the scalability of the biomass-based energy systems. Future studies should also focus on the economic feasibility and lifecycle assessment of the biomass-to-energy process for their sustainability and competitiveness in the global energy market. This research can pave the way for the innovative strategies in biomass waste management, in order to promote a circular economy for with the less reliance on fossil fuels.

Garden wastes have posed significant challenges to waste management and environmental sustainability. One type of thermochemical conversion, the pyrolysis, can transform biomass into biochar, bio-oil, and syngas. This study aimed to explore the high-value utilization of garden wastes using pyrolysis. Three typical garden plant leaves—coniferous leaves (Pinus sylvestris Linn. var. mongolica Litv.), broad leaves (Amygdalus triloba (Lindl.) Ricker), and herbaceous plants (Setaria viridis (L.) P. Beauv.)—were systematically investigated using thermogravimetric analysis (TGA). A kinetic model was established to determine the effects of leaf type, particle size (0.053-0.250 mm), and heating rate (10–20 °C/min) on the pyrolysis process. The TGA experiments were conducted under a nitrogen atmosphere for an inert environment, with the temperature ranging from room temperature to 800 °C. The heating rates were varied at 10, 15, and 20°C/min. The particle sizes of the samples were classified into three ranges (0.053-0.15, 0.15-0.25, and 0.053-0.25 mm). Their influence on the pyrolysis efficiency and residual amounts was examined after experiments. The results show that the pyrolysis processes of the three types of leaves all exhibited four-stage characteristics, namely the dehydration, slight weight loss, rapid pyrolysis, and carbonization stages. The optimal pyrolysis conditions were determined for the coniferous leaves, broad-leaved leaves, and herbaceous plants. In coniferous leaves, the optimal particle size and heating rate were 0.053-0.15 mm and 10 °C/min, respectively. In broad-leaved leaves, the optimal conditions were 0.15-0.25 mm and 10 °C/min. In herbaceous plants, the optimal conditions were 0.15-0.25 mm and 15 °C/min. The final residues were ranked in descending order of the coniferous leaves, herbaceous plants, and broad-leaved leaves under these optimal conditions. The three-element analyses showed that there were some differences in the contents of cellulose, hemicellulose, and lignin in the leaves. Woody plants with a higher lignin content shared the higher thermal stability and thus a higher residue amount. In contrast, the herbaceous plants with a lower lignin content and a higher cellulose content were more easily decomposed, indicating the lower residue amount. The pyrolysis kinetic analysis was conducted using the Coats - Redfern integral method. The reaction activation energies of the coniferous, broad-leaved, and herbaceous leaves were 15 837.41, 12 271.75, and 8 676.48 kJ·mol^-1, respectively. The pyrolysis difficulty levels were ranked in descending order of the coniferous leaves, broad-leaved leaves, and herbaceous leaves, which was consistent with the thermogravimetric analysis curves. This finding can provide the key process parameters for the directional pyrolysis conversion of garden wastes. It is also significant to optimize the biomass char preparation and the resource utilization of garden wastes.