Advancing Renewable Energy Solutions through the Co-HTC of Cattle Manure and Hemp Stalk Residues

The increasing demand for environmental sustainability practices has highlighted the need for efficient recovery, valorization, and utilization of waste residues, including those in the agricultural sector. This study focuses on the co-hydrothermal carbonization (co-HTC) of organic system cattle manure (OSCM) and hemp stalk residue to enhance the combustion performance of the hydrochar and evaluate the quality of process water for bio-hydrogen production. The influence of HTC reaction temperature (180, 220, 260 °C) as well as the synergistic effect of the mass mixing ratios of the two biomasses (1:0, 3:1, 1:1, 1:3, 0:1) was investigated. The physicochemical characteristics of the samples were determined through proximate, ultimate, and compositional analysis, while thermogravimetric analysis (TGA) was used for determining the combustion behavior and performance. Moreover, a hybrid Analytic Hierarchy Process (AHP) – Entropy – TOPSIS multicriterial analysis was performed for ranking hydrochar samples. Key findings indicate the positive synergistic effect of the mixing ratio on hydrochar characteristics, significantly improving carbon content and heating value, thereby enhancing its combustion performance and organic content in process water. The results indicate that the HY0.7:0.3 at 260 °C achieved the highest rank, demonstrating superior performance across the evaluated criteria. In contrast, HY1:0 (hydrochar hemp) at 220 °C was ranked lowest, particularly due to lower combustion performances. This integrated approach not only addresses the challenges of utilizing cattle manure and hemp stalk as energy sources but also contributes to sustainable waste management practices. The findings provide a pathway for future studies aimed at optimizing biomass conversion technologies and promoting circular economy principles in the agricultural sector.