Biochar from pruned Ficus benjamina branches: Carbonization temperature effects on properties and applicability as solid biofuel and soil amendment applications

Abstract

The pruned branches of Ficus benjamina represent an underutilized lignocellulosic biomass with high thermochemical conversion potential. This study investigated the effect of the carbonization temperature (400, 500, and 600 °C, residence time of 2 h) on the physicochemical, energetic and structural properties of the biochar produced and determined its potential as a solid biofuel and soil amendment. Proximate and elemental analysis, BET surface area, carbon stability assessment, higher heating value (HHV) determination, and polycyclic aromatic hydrocarbons (PAHs) quantification using UHPLC-FLD were performed. Increasing the carbonization temperature resulted in a significant reduction in energy yield, volatile content, and hydrogen content. However, the ash content (10.49 to 13.41 wt.%), carbon (66.71 to 68.93 wt.%), electrical conductivity (1.48 to 3.21 dS m-1), and BET area (3.49 to 26.04 m2 g-1) increased. PAHs concentrations remained within safe limits (23.40 to 160.17 μg kg-1). The HHV ranged from 24.23 to 26.07 MJ kg-1, comparable to sub-bituminous coal and charcoal. Increasing the temperature significantly improved the stability of the biochar. The mean residence times ranged from 1627 to 1734 years, indicating a high carbon sequestration potential. The biochars produced meet international standards (IBI and EBC). Biochar produced to 500 °C showed an optimal balance between energetic, structural, and chemical stability properties. The results show that carbonization of the pruned branches of Ficus benjamina is presented as a viable technology for the production of value-added biochar, as a solid biofuel, and as a soil amendment with carbon sequestration capacity.