Intermittent electric field stimulated reduction-oxidation coupled process for enhanced azo dye biodegradation

The electro-stimulated microbial process offers promise in overcoming the intrinsic drawbacks of the conventional reduction-oxidation process for azo dyes removal. However, the lack of available electron donors, continuous external power supply, and weak anodic oxidation are the major challenges for this process to achieve efficient azo dye biodegradation. Herein, an intermittent electric field stimulated reduction-oxidation coupled process was developed to enhance Alizarin Yellow R (AYR) biodegradation. Introducing a weak inter-mittent electrostimulation considerably boosted the anaerobic cathodic reduction and micro-oxygen-assisted anodic oxidation process, as evidenced by the higher AYR decolorization, p-phenylenediamine, and 5-aminosa-licylic acid bio-mineralization efficiency than that in the bio-processes with continuous and without electro-stimulation, respectively. The endogenous organics generated during AYR degradation could serve as an effective electron source for anodic microorganisms to drive the biocathode decolorization. Compared to continuous electrostimulation, intermittent electrostimulation exhibited better electron transfer capability and created a more favorable oxidation-reduction potential (ORP) for reductive decolorization of AYR and bio-mineralization of its intermediate products. Microbial community analysis revealed that more functional consortia capable of electroactivity (e.g. Geobacter and Pseudomonas) and AYR metabolism (e.g. Bosea, Sphingopyxis, and Achromo-bacter) were enriched by intermittent electrostimulation than continuous electrostimulation. The molecular ecological network analysis indicated that synthetic metabolisms between electroactive and AYR metabolizing bacteria might play major roles in electro-microbial-mediated AYR removal. This study reveals the potential and mechanism of intermittent electric field stimulated reduction-oxidation coupled process for enhanced azo dye biodegradation, which opens an appealing avenue for enhanced azo dye removal from wastewater.