Enhanced biodegradation of reactive blue 221 by Arthrobacter and micrococcus in sludge wastewater: Comparative analysis and electrochemical insights

This study investigated the decolorization potential of two bacterial species, Arthrobacter and Micrococcus , for the textile dye Reactive Blue 221 (RB221). Decolorization and bacterial growth were monitored spectrophotometrically at 615 nm and 600 nm, respectively, over 24, 48, 72, and 96 hours. Decolorization was evaluated under five culture conditions: nutrient broth, mineral salt medium (MSM), MSM supplemented with glucose, MSM supplemented with yeast extract, and MSM supplemented with both yeast and glucose extract. The dye color progressively faded over time, with a noticeable decrease in absorbance at each time interval with increasing growth of Arthrobacter spp. Among the bacterial isolates, Arthrobacter sp. achieved the highest decolorization (98.75%) after 96 h in MSM supplemented with yeast extract, while activated sludge (SWW, an indigenous sewage sludge community) showed the highest overall decolorization (99.13%) in NB. Arthrobacter outperformed Micrococcus in decolorization capability, indicating its potential for further optimization in textile wastewater treatment. Electrochemical analysis revealed that RB221 undergoes electroreduction at approximately -0.2 V vs. SCE. Subsequent electrolysis at around -0.3 V for 45 minutes led to significant dye degradation, as confirmed by UV-Vis spectroscopic results. The results of the cyclic voltammetry experiment show that the reduction of 1 mM RB 221 on a platinum disc electrode starts around -0.2 V in 0.1 M aqueous KCl at room temperature. Successive scans indicate dye adsorption during electroreduction, with a 40% drop in current in the second scan and negligible change thereafter. Higher initial RB 221 concentration leads to a slight shift towards a less negative potential, likely due to easier reduction facilitated by dye molecules already present on the surface. These findings suggest that integrating bacterial and electrochemical methods could enhance dye degradation efficiency and rate, offering a promising approach for improving textile wastewater treatment processes.