Enhancing Fuel Properties and Energy Performance with Co-Hydrothermal Carbonization of Coffee Waste and Swine Manure

This study evaluates the fuel properties and energy performance of hydrochar produced through co-hydrothermal carbonization (Co-HTC) of swine manure (SM) and coffee waste (CW). The effects of reaction temperature (160°C, 200°C, 240°C) and mixing ratio (SM:CW = 1:1, 3:1, 5:1) on combustion characteristics, energy densification ratio (EDR), and energy yield (EY) were analyzed. The results indicate that Co-HTC effectively enhances fuel quality by leveraging the synergistic interactions between SM and CW. At 240°C and a 1:1 mixing ratio, the produced hydrochar exhibited a combustion characteristic index (S) of 9.1 × 10⁻⁹ %²/min²·°C³, an EDR of 1.39, and an EY of 57%, demonstrating superior fuel performance. The high lignin content in CW promoted fixed carbon retention, while the elevated nitrogen content in SM contributed to potential agricultural applications. Additionally, Co-HTC effectively reduced O/C and H/C atomic ratios, resulting in enhanced energy density. Despite an increase in ash content with higher SM ratios, EY values remained high across all conditions, with a maximum of 61.8% at a 5:1 ratio, suggesting that energy retention was not significantly hindered. These findings confirm that Co-HTC is a viable approach to converting organic waste into high-energy-density solid fuel, offering a sustainable solution for bioenergy production and waste valorization.