Pilot-Scale Valorization of Food Waste using Eucalyptus grandis-Derived Biochar: Functional Roles in pH Modulation, Volatile Fatty Acid Dynamics, Microbial Network Transitions, and Preliminary Technoeconomic Assessment

Abstract Biochar is increasingly recognized in biorefineries for its unique physicochemical properties that enhance microbial performance and process stability. However, limited research has examined its biocatalytic functions in food waste valorization, particularly in the Global South regions. This study investigates the functional roles of Eucalyptus grandis -derived biochar in a pilot-scale anaerobic system, emphasizing pH modulation, volatile fatty acids (VFAs) dynamics, microbial network transitions, and technoeconomic studies. Comprehensive biochar characterization using FTIR, BET, SEM, TGA, XRD, and CHNS analyses revealed favorable surface functionality, porosity, and nutrient content conducive to microbial colonization. Biochar addition maintained a stable pH range of 7.03–5.0, contrasting with the sharper decline observed in the control (7.03–4.30). Acetic acid was the dominant VFA, with a markedly higher relative proportion in the biochar-amended reactor (53.23%) than in the control (15.23%). Nutrient recovery in the resulting biofertilizer was also enhanced, attaining 92.12 ± 0.13, 682.08 ± 0.21, and 4238.06 ± 0.05 mg/L for nitrogen, phosphorus, and potassium (NPK), respectively. Enhanced VFA depletion indicated stimulated syntrophic activity, corroborated by microbial community analysis, which showed enrichment of Pseudomonadota and Campylobacterota , taxa pivotal to syntrophic metabolism and carbon flux regulation. Preliminary techno-economic studies also confirmed the cost-effectiveness of biochar in food waste biorefineries. These findings demonstrate that Eucalyptus grandis biochar functions as a sustainable, low-cost bioadditive that enhances biocatalytic efficiency and nutrient recovery in food waste valorization. This work establishes a scalable biorefinery model for a biochar-mediated bioprocess that advances circular bioeconomy principles and promotes environmental and socioeconomic resilience in developing regions.