Thermodynamic Insight into Polarity Reversal-Mediated Hub-Functional Microbiome Assembly for Accelerated Biocathode Formation in Bioelectrochemical Systems

This study developed a method for constructing hub-functional (HF) microbiomes based on an established polarity-reversal strategy and thermodynamic analysis, with nitrate as the cathodic electron acceptor. XDLVO theory analysis revealed that the slow startup of traditional biocathodes stemmed from strong Lewis acid−base repulsion, which could be greatly diminished by polarity reversal. For instance, at −0.5 V (vs Ag/AgCl; hereafter the same), the repulsion was reduced by 36610.39 KT, promoting microbial adhesion. Electrochemical, microbial, and physicochemical characterizations confirmed that the HF microbiomes established a synergistic metabolic interaction. Hub microorganisms acted as electron transfer bridges, while functional microorganisms realized efficient NO3−-N reduction. The optimal potential for directed formation of HF microbiomes was −0.5 V, achieving a NO3−-N removal efficiency of 91.1% and shortening the biocathode startup period compared to the nonpolarity reversal mode. Microbial community analysis showed that the HF microbiomes were dominated by electroactive hub genera (e.g., Rhodopseudomonas) and denitrifying functional genera (e.g., Paracoccus, norank_f_Chitinophagaceae), which synergistically enhanced electron transfer efficiency. This study provides a novel thermodynamic insight into directed microbiome regulation in BESs and solves the bottleneck of slow traditional biocathode formation, offering a promising approach for nitrate remediation.