Multiresponse Optimization of Hydrothermal Carbonization of Yard Waste Using Box-Behnken Design and Desirability Function Analysis

The present study investigates the hydrothermal carbonization of yard waste using box-Behnken design (BBD) to optimize key process parameters for enhanced fuel properties. The influence of temperature (180°C–240°C), residence time (240–480 min), and solids concentration (5%–15%) on the quality and yield of hydrochar was evaluated. Response surface methodology was employed to model and analyze the responses: mass yield, carbon content, higher heating value (HHV), and energy yield. Desirability function analysis was integrated to simultaneously maximize the HHV and carbon content while ensuring efficient conversion through optimal yield. The optimal conditions predicted were 220°C, 240 min, and 15% solids, yielding a desirability of 0.964 and energy yield of 62.98%. The analysis underscores the effectiveness of BBD in understanding parameter interactions with fewer experiments, enabling reliable and sustainable valorization of yard waste. By integrating desirability analysis with BBD and focusing on a heterogeneous urban biomass such as yard waste, the study offers a comprehensive process optimization framework that extends beyond conventional agricultural feedstocks and single-response approaches. The outcomes support an efficient and scalable pathway for converting lignocellulose yard residues into value-added hydrochar, aligning with sustainable waste-to-energy and circular bioeconomy strategies.