Analysis of thermal characteristics of seaweeds, Spatoglossum asperum and Ulva rigida for utilisation as a feedstock for biochar production

Abstract

Biochar is a carbon-rich, porous material produced from biomass through thermochemical processes, with properties largely determined by the feedstock. This study evaluates the thermal characteristics of two locally abundant seaweeds, Spatoglossum asperum and Ulva rigida, sourced from the Kollam coast of Kerala, to assess their suitability as sustainable feedstocks for biochar production. Proximate and ultimate analyses indicated that S. asperum is a superior biochar feedstock, owing to its higher carbon content and lower ash and sulfur contents compared with U. rigida. Thermogravimetric analysis revealed three different zones for both cases. Kinetic modelling using the Coats–Redfern method yielded activation energies of 15–16 kJ/mol, indicating similar first-order degradation mechanisms. Biochar yield decreased as thermochemical reaction temperature increased, while ash content increased. Biochars produced at 300 °C showed the highest yield, with S. asperum exhibiting more favourable properties for biochar applications than U. rigida. FTIR analysis confirmed the transformation of biochar produced at 300 °C into a more aromatic carbon structure, while SEM demonstrated improved surface morphology. Compared with Ulva rigida, Spatoglossum asperum exhibited lower sulfur content, lower O/C ratios at higher temperatures, and more favourable elemental characteristics, highlighting its greater potential as a sustainable feedstock for high-quality biochar production.