Hydrochars from agricultural and forestry waste designed to achieve multipurpose matrices: Modeling and optimization of process parameters

• Hydrothermal carbonization of vine shoots and spruce bark biomass • Optimization of hydrochar features in relation to the aimed application • SEM-EDX and WEKA- segmentation-based porosity analyses were performed • Mass Yield and Conversion Degree of VS and SB were considered HTC responses • Optimal HTC parameters improve the overall performance of hydrochar production Agricultural and forestry waste biomass constitutes sustainable feedstock for the production of value-added products. Hydrothermal carbonization (HTC) of vine shoots (VS) and spruce bark (SB) biomass was employed to produce hydrochars with tailored properties for various applications, including pollutant adsorption, carbon sequestration, microbial immobilization, soil conditioning, wastewater treatment, catalysts, and bio-composites. This paper reports a modeling and optimization approach applied to screen and enhance the features of hydrochars converted from VS and SB. For this purpose, an experimental design was built considering three independent variables: temperature ranged from 230 and 290°C, residence time, 30 up to 90 minutes, and solid-to-liquid ratio 1:5 to 1:10 g/mL. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), and WEKA-segmentation-based porosity analysis were used to characterize the optimal features of hydrochars. HTC processing at 260°C, 30 min, and a 1:10 w/v ratio significantly modified these structures, producing VS hydrochar (VS-HC) with a honeycomb-like porous matrix and SB hydrochar (SB-HC) with denser, finer pores. Quantitative analysis using the Trainable Weka segmentation plugin in ImageJ confirmed 73 pores per 2500 μm² (50 μm × 50 μm) with an average size of 0.9 μm² for VS-HC, and 133 pores per 2500 μm² with 0.6 μm² for SB-HC, correlating with their porosities and biomass compositions. Though a temperature of 260°C, 30 min of residence time and a w/v ratio of 0.1 proved to be effective parameters in achieving desirable outcomes, constrained optimization approaches may further enhance energy efficiency and reach the aimed biomass conversion. This provides a pathway for refining HTC parameters to improve the overall sustainability and performance of hydrochar production.