Synergistic Microbial and Abiotic Mechanisms of Mineral-Driven Humic Acid Evolution for Soil Remediation

This study investigated how manganese mineral addition enhanced the extracellular electron transfer (EET) capacity of humic acids (HAs) in soil bioelectrochemical systems. Through electrochemical analysis, EEM-PARAFAC, hetero-2DCoS, and structural equation modeling, two complementary transformation pathways of HA components were identified. The first was a microbial-driven aromatic condensation that converted intermediate Component 2 into aromatic-rich, electron-accepting Component 3. The second was an abiotic Mn4+-mediated oxidative fragmentation that produced low-molecular-weight, electron-donating Component 1. These dual processes increased the redox heterogeneity of the HA matrix and supported bidirectional electron shuttling, facilitating continuous redox cycling for pollutant degradation, which enhanced system performance, resulting in a 23% higher phenanthrene removal efficiency and nearly 2-fold greater power density. The findings established a mechanistic basis for the synergistic microbial and abiotic regulation of humic substances, offering new insights for sustainable soil remediation.