Mechanistic insights into simultaneous acid red GR removal and electricity generation in a static magnetic field-assisted pilot-scale red soil microbial fuel cell.

The simultaneous removal of refractory azo dyes and recovery of bioelectricity remains a major challenge for microbial electrochemical technologies because of the limited efficiency of extracellular electron transfer (EET). In this study, three red soil microbial fuel cells (RSMFCs) were constructed, including a static magnetic field-assisted sodium acetate co-substrate system (MFSAR), a sodium acetate co-substrate system without magnetic field (SAR), and a single-substrate system fed with Acid Red GR (AR), to evaluate the effects of magnetic field stimulation and single substrate Acid Red GR on pollutant removal and bioelectricity generation. MFSAR exhibited improved electrochemical performance, including higher output voltage, exchange current, and total charge capacity, accompanied by enhanced decolorization and organic pollutant removal efficiencies. Interestingly, Acid Red GR serving as the sole substrate, could sustain a certain level of electron transfer activity. GC-MS analysis suggested that Acid Red GR underwent azo bond cleavage, ring opening, and subsequent mineralization in MFSAR. Metagenomic analyses revealed that the magnetic field selectively enriched electroactive bacteria (e.g., Geothrix, Anaeromyxobacter, Thiobacillus) and viral (e.g., Waedenswilvirus, Nanhaivirus, Triduovirus), while suppressing the excessive proliferation of some fungal (e.g., Hortaea, Cladosporium, Metarhizium). Functional metagenomic analysis further demonstrated the enrichment of pathways related to carbon oxidation, respiratory electron transport, and energy conservation in MFSAR, including glycolysis, tricarboxylic acid cycle, quinone-dependent electron transport, cytochrome oxidases, and ATPases. These findings demonstrate that magnetic fields can establish an efficient bioelectrochemical network, thereby providing a promising strategy for the treatment of dye wastewater and simultaneous bioenergy recovery.