Thermochemical conversion of water hyacinth biomass into biochar and value-added products: mechanical design and experimental validation

Abstract The uncontrolled proliferation of water hyacinth in freshwater ecosystems represents a persistent environmental and energy-related challenge. While numerous biomass utilization strategies have been reported, the development of validated thermochemical conversion systems capable of transforming this invasive resource into stable value-added products remains limited. This study introduces mechanical design, numerical validation, and experimental assessment of a thermochemical conversion system for transforming water hyacinth into biochar and bioactive liquid fractions. An additional lab-scale pyrolysis experiment was performed to evaluate the functionality of value-added products (biochar and pyroligneous acid) generated through the thermochemical conversion process. The proposed system consists of a compact horizontal pyrolysis reactor equipped with an internal auger mechanism, external heating system, thermal insulation, and vapor condensation unit. Critical structural and thermal components were numerically validated using finite element analysis (FEA) to ensure mechanical integrity and safe operation under elevated temperature conditions. Results of FEA confirmed the adequate structural integrity, thermal stability, and operational safety under pyrolysis conditions. FEA analysis further confirmed the remaining of bending and thermal stress below the yield strength of stainless steel 304. The proposed thermal insulation exhibited high efficiency toward minimizing heat losses, maintaining safe external temperatures, and keeping thermal stress within material capacity. Engineered biochar produced at 400, 500, and 600°C was comprehensively characterized using spectroscopic (SEM, AFM, EDS, XRD, DSC, and FTIR), physical (specific surface area, pore volume, pore radius, and zeta potential), and chemical (ICP, pH, and EC) analyses. Characterization results confirmed the high functionality of biochar, including porous structure, high surface area, and abundance of active functional groups. Results also showed that increasing pyrolysis temperature was associated with enhancement of porosity, aromatization, and crystallinity. GC–MS and ICP analysis of pyroligneous acid showed also abundance of several compounds previously associated with antimicrobial, antioxidant, and plant-defense-related activities, alongside with considerable macro and micronutrients. Findings from this study, therefore, provide a validated engineering and experimental framework for invasive biomass valorization, contributing to circular bioenergy strategies and sustainable agriculture management.