Upcycling nutrient-enriched biochar for circular carbon pathways in bioenergy production with thermokinetic and life cycle assessment
Journal
Journal of Environmental Chemical Engineering
Journal Volume
14
Journal Issue
3
Start Page
122402
ISSN
22132929
Date Issued
2026-06
Author(s)
Abstract
This study presents a circular carbon pathway integrating nutrient-enriched biochar amendments and recovered biochar (RB) reuse to optimize the pyrolytic conversion of Pennisetum purpureum in a water-carbon-energy nexus. Biomass cultivated under biochar (BC) treatments exhibited improved fuel characteristics, including fixed carbon (26.56 wt%), aromaticity (O/C 0.942, H/C 0.147), and higher heating value of 17.43 MJ/kg. SEM/EDS confirmed porous BC framework with carbon and oxygen dominated composition. FTIR showed treatment-dependent surface chemistry changes between pristine BC and RB, including strengthened oxygenated/mineral-associated bands in RB, consistent with functional group evolution during the use-recovery cycle. Thermogravimetric evaluation at five heating rates (5, 8, 10, 15, 20 °C/min) confirmed multi-stage decomposition with heating-rate-dependent shifts in the main devolatilization peak, confirming kinetically heterogeneous thermal degradation. Model-free iso-conversional kinetics (FWO, KAS, and nonlinear Vyazovkin) quantified conversion-dependent apparent activation energies, with the most reliable fits in the main devolatilization window (α = 0.2–0.6, R2 ≥ 0.98) and greater uncertainty at high conversion (α≥0.7) due to late-stage kinetic heterogeneity. Peak-based Kissinger analysis yielded stable activation descriptors across treatments (Ea = 73.92–97.88 kJ/mol) and corresponding activation thermodynamics (ΔH = 69.01–92.98 kJ/mol, ΔG = 173.21–175.25 kJ/mol, ΔS = −0.138 to −0.180 kJ/mol.K), interpreted as non-equilibrium activation parameters rather than equilibrium spontaneity. LCA showed RB reuse shifted modelled net climate impact from positive control values (1.0 ×10−2 kg CO2-eq.MJ) to net-negative balance (-2.8 ×10−2 kg CO2-eq.MJ), driven by biogenic CO2 uptake flows. This framework establishes a mechanistic baseline for engineering carbon-negative feedstocks aiming at green energy production and global sustainability mandates.
Subjects
Bioenergy
Carbon sequestration
Life cycle assessment
Pyrolysis
Resource circularity
Publisher
Elsevier Ltd
Type
journal article