Integrated Bioelectrochemical Conversion of <i>Bacillus subtilis</i>-Pretreated Sugar Cane Bagasse: Metabolic Profile Optimization for Enhanced Microbial Fuel Cell Efficiency and Sustainable Biorefinery Applications

Lignocellulose recalcitrance remains a significant economic challenge in modern biomass conversion processes. Microbial strategies offer considerable promise for ecofriendly bioenergy generation. This study presents an advanced integrated approach that combines bacterial treatment with a bioelectrochemical system (BES) to enhance the conversion efficiency of lignocellulosic biomass. Unlike integrated or sequential approaches, a comparative evaluation of two distinct pretreatment strategies, alkaline delignification and biological treatment, was conducted independently to assess their individual effectiveness in sugar cane bagasse (SCB) degradation and their performance in a microbial fuel cell (MFC). Biological treatment with <i>B. subtilis</i> alone yielded superior outcomes in terms of saccharification efficiency, microbial growth, and bioelectricity generation, as evidenced by higher open-circuit potentials in MFC half-cell studies in comparison with alkali delignified SCB. Notably, <i>B. subtilis</i> treatment increased cellulose content by 72% and reduced hemicellulose and lignin by approximately 0.84-fold, indicating effective enzymatic action. Metabolomic profiling identified 2846 metabolites that significantly diverged between the experimental groups. Notably, lignin-derived compounds such as ferulic acid, syringic acid, and p-coumaric acid were detected at elevated levels, confirming enhanced ligninase activity in pretreated SCB. Additionally, the presence of organic acids (e.g., acetic acid), amino acids, and their derivatives, resulting from the breakdown of cellulose, hemicellulose, and lignin, provided essential bioenergy substrates for exoelectrogenic organisms in BESs. This integration led to a maximum power density of 353 ± 5 mW/m² and a current density of 200 ± 3 mA/m², demonstrating significant enhancement in performance of MFC. Furthermore, the biotransformation of SCB facilitated the channeling of metabolites into value-added products, increasing the overall efficiency of the biomass valorization. Thus, the rational utilization of SCB underscores its potential for scalable biorefinery applications and its broader implications for sustainable bioenergy production.