Pirólise lenta do aguapé (Eichhornia crassipes) para obtenção de biocarvão visando ao sequestro de carbono

Abstract

Water hyacinth (Eichhornia crassipes), an invasive aquatic macrophyte characterized by rapid growth and commonly associated with eutrophication processes, represents an abundant and underexploited source of renewable carbon. This study aimed to evaluate the yield, physicochemical properties, and carbon sequestration potential of biochar produced via slow pyrolysis of water hyacinth biomass. In particular, the effects of final pyrolysis temperature (400, 500, and 600 °C) and residence time (30 and 60 min) on the specific greenhouse gas (GHG) emissions avoided per ton of dry biomass were investigated. Proximate analysis revealed moderate contents of fixed carbon (13.07%) and ash (27.41%), associated with significant concentrations of K (676.9 mgK/gash), Ca (65 mgCa/gash), and P (27.3 mgP/gash). These results highlight the suitability of water hyacinth as a feedstock for biochar production with potential agronomic applications and contributions to nutrient cycling. Elemental analysis indicated proportions of C (30.61%), O (35.53%), H (3.78%), N (2.35%), and S (0.32%), values consistent with those typically reported for biomass feedstocks used in slow pyrolysis processes. However, the low bulk density of the biomass (145.33 kg/m⁻³) imposes logistical constraints, requiring additional preprocessing steps in practical applications, such as briquetting or pelletization. Biochar yield decreased from 0.48 tbiochar/tbiomass (400 °C; 30 min) to 0.34 tbiochar/tbiomass (600 °C; 60 min), reflecting the increased intensity of devolatilization and thermal cracking reactions at higher temperatures and longer residence times. The elemental carbon fraction ranged from 0.36 to 0.18, while the molar H/C ratio decreased from 0.71 to 0.48, indicating increased aromaticity and recalcitrance of the carbon matrix. The stable carbon fraction (Fperm) ranged from 0.51 to 0.66, with higher values observed at elevated temperatures and longer residence times. Specific avoided GHG emissions ranged from 0.32 to 0.15 tCO₂eq/ t of dry biomass, suggesting that milder temperature conditions combined with longer residence times may enhance the overall carbon sequestration potential. From an economic– environmental feasibility perspective, water hyacinth-derived biochar shows the potential to generate carbon credits ranging from US$ 22.89 to US$ 50.37 per ton. Overall, the findings indicate that biochar produced from water hyacinth exhibits physicochemical characteristics compatible with applications in carbon sequestration and soil quality improvement. Moreover, its production represents a promising strategy for the sustainable management of invasive aquatic plants within the framework of a low-carbon bioeconomy.