Graphene oxide bioaugmentation of E. coli enables nutrient-free, light-independent methylene blue removal via spontaneous bio–nano flocculation

The contamination of water bodies with dye pollutants, particularly methylene blue (MB), represents a significant environmental challenge due to the widespread use in industries such as textiles, pharmaceuticals, and cosmetics. Effective removal of MB from wastewater is essential to prevent ecological damage and safeguard human health. Various techniques have been explored globally for dye segregation, including adsorption methods utilizing light activated nanomaterials such as graphene oxide combined with catalytic metal atoms and bioremediation employing bacteria. Enzymes are also widely studied but are prone to biocatalyst deactivation due to denaturation. Also, some bacteria, such as E.coli, are sensitive to MB and this represents a limiting step for highly concentrated MB solutions. Among these methods a light independent self-sustained strategy has not been developed. Indeed, even if carbon materials such as graphene oxide are efficient, their efficacy in the absence of light exposure is limited. In this paper, we demonstrate a novel spontaneous flocculation method combining graphene oxide and Escherichia coli bacteria for the efficient removal of MB from aqueous solutions. Spectroscopic analysis confirms significant dye removal efficacy through the formation of flocs, highlighting a synergistic interaction between graphene oxide and bacterial cells. E. coli is considered a non-decolorizer bacterium but in presence of graphene oxide cells is trapped and water decolorization is fostered on the surface of the nanomaterial. We also demonstrate that infrared light (805 nm) can be used to inactivate bacteria thanks to an enhanced NIR adsorption of MB deposited on graphene oxide flakes. The detoxification method of wastewater containing methylene blue, based exclusively on the use of graphene oxide and without the addition of iron- or copper-based metallic particles, prevents the introduction of additional inorganic contaminants into the environment. Our findings not only validate the effectiveness of this combined approach but also suggest its potential for scalable applications in wastewater treatment, providing an innovative and eco-friendly solution to address global water pollution challenges.