Mechanistic insights into methylene blue biodegradation by Tetradesmus obliquus: a multimodal approach using absorption, fluorescence, and square wave voltammetry

Industrial dye wastewater production has surged alongside rapid industrial growth. This study evaluates the biodegradation of methylene blue (MB) by Tetradesmus obliquus, utilizing spectroscopical and electrochemical techniques to monitor effectiveness. Biodegradation model reveals conditions and pathways involved. Tetradesmus obliquus exhibits robust dye degradation, reducing absorbance at 664 nm significantly within days. MB concentrations of 2-4 mg/L were nearly completely degraded by day 6 and fully by day 9, with higher concentrations gradually reduced over 14 days. Square wave voltammetry showed full degradation of 0.2 mg/L MB by day 9. Fluorescence spectral analysis highlighted red-shifted emissions and decreased intensity due to MB presence. Growth patterns indicate Tetradesmus obliquus thrives post-MB adsorption, producing extracellular superoxide and hydrogen peroxide that convert MB to CO₂, NO₂, and H₂O. Spectroscopic and electrochemical data confirm MB breakdown while boosting algal growth. This study demonstrates Tetradesmus obliquus's efficacy in biodegrading MB from industrial textile wastewater, removing residual dye-bath additives and promoting environmental sustainability.