Frequency-modulated alternating current-driven bioelectrodes for enhanced mineralization of Alizarin Yellow R

The alternating current (AC)-driven bioelectrochemical process, in-situ coupling cathodic reduction and anodic oxidation in a single electrode, offers a promising way for the mineralization of refractory aromatic pollutants (RAPs). Frequency modulation is vital for aligning reduction and oxidation phases in AC-driven bioelectrodes, potentially enhancing their capability to mineralize RAPs. Herein, a frequency-modulated AC-driven bioelectrode was developed to enhance RAP mineralization, exemplified by the degradation of Alizarin Yellow R (AYR). Optimal performance was achieved at a frequency of 1.67 mHz, resulting in the highest efficiency for AYR decolorization and subsequent mineralization of intermediates. Performance declined at both higher (3.33 and 8.30 mHz) and lower (0.83 mHz) frequencies. The bioelectrode exhibited superior electron utilization, bidirectional electron transfer, and redox bifunctionality, effectively aligning reduction and oxidation processes to enhance AYR mineralization. The 1.67 mHz frequency facilitated the assembly of a collaborative microbiome dedicated to AYR bio-mineralization, characterized by an increased abundance of functional consortia proficient in azo dye reduction (e.g., Stenotrophomonas and Shinella), aromatic intermediates oxidation (e.g., Sphingopyxis and Sphingomonas), and electron transfer (e.g., Geobacter and Pseudomonas). This study reveals the role of frequency modulation in AC-driven bioelectrodes for enhanced RAP mineralization, offering a novel and sustainable approach for treating RAP-bearing wastewater.