Regulation of slow-release performance of high-sugar biomass waste filter mud and sugarcane bagasse by co-hydrothermal carbonization and potential evaluation of hydrochar-based slow-release fertilizers

In this study, we investigated the impact of process parameters, including reaction temperature (180–300 °C), residence time (30–120 min), and mixing ratios (1:0∼5:1), on hydrochar properties of high-sugar biomass waste filter mud and sugarcane bagasse in the co-hydrothermal carbonization. The hydrochar is comprehensively characterized using Proximate analysis, industrial analysis, scanning electron microscopy, multi-point Brunauer-Emmett-Teller, Fourier-transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The urea release patterns from hydrochar-based slow-release fertilizers were assessed across different hydrochar-to-fertilizer ratios, and the reaction path during co-hydrothermal carbonization was analyzed. The findings reveal that hydrochar produced 240°C-60min-5:1 had a notably high specific surface area (45.921 m²/g), abundant functional groups, and exceptional adsorption capabilities, which was suitable for preparing slow-release fertilizers. The hydrochar-based slow-release fertilizer formulated at a hydrochar-to-fertilizer ratio of 5:1 had the optimal slow-release performance, and the cumulative release rate of urea in 7d was 49.65 %, which was more than 40 % lower than that of pure urea. These results underscore the promising agricultural applications of products derived from the co-hydrothermal carbonization of filter mud and sugarcane bagasse.