Influence of sonication duration pretreatment on thermal degradation behavior and pyrolysis kinetics of raw and pretreated spent mushroom substrate (SMS)

This study reveals that sonication-assisted acid leaching, particularly with a 20-min sonication duration (SMS20), offers a highly effective pretreatment method for Spent Mushroom Substrate (SMS), significantly reducing its ash content and enhancing its suitability as a bioenergy feedstock. While SMS is a promising bioenergy resource, its high alkali and alkaline earth metal (AAEM) content leads to elevated ash levels, causing operational challenges such as slagging, fouling, and reduced pyrolysis efficiency. Previous kinetics studies often overlooked the comprehensive thermal degradation behavior across all major decomposition stages. Therefore, this study investigated the effect of sonication-assisted acid leaching on the thermal degradation behavior and activation energy of SMS across three decomposition sections corresponding to moisture removal, hemicellulose degradation, and cellulose degradation. The ash content was significantly reduced from 19.766 %, in raw SMS to 5.161% in the SMS20 sample, while volatile matter increased to 72.286%, indicating enhanced thermal reactivity. Thermal analysis revealed four distinct degradation regions: moisture removal (30–61 °C), hemicellulose decomposition (140–280 °C), and cellulose decomposition (280–360 °C), Char formation (700-1000 °C). Activation energy analysis showed that the pretreatment reduced the energy required for moisture removal and cellulose degradation. In the hemicellulose region, activation energy varied among the pretreated samples, indicating that the pretreatment altered the thermal stability of this fraction depending on the sonication duration. Notably, SMS20 exhibited the lowest activation energy in both the hemicellulose and cellulose regions, demonstrating the highest thermal reactivity among all samples. These findings confirm that a 20-min sonication-assisted acid leaching pretreatment is the optimum condition for enhancing the pyrolysis performance of SMS for thermochemical conversion by minimizing ash content and improving pyrolysis characteristics. Schematic workflow of the pyrolysis of acid-leached Spent Mushroom Substrate (SMS). the process involves biomass preparation (drying, grinding, and sieving to 250 µm), followed by 1% HNO3 acid leaching assisted by sonication (5–25 min). Thermogravimetric analysis (TGA) was employed to characterize the thermal decomposition stages (moisture, volatiles, fixed carbon, and ash). Kinetic parameters, including activation energy (Ea) and pre-exponential factor (A), were determined using the Coats-Redfern integral method through linear regression of ln[-ln(1-α)/T2] versus 1/T. This schematic diagram was generated using Manus AI.