Notice of Retraction: Microbial degradation of chromium azo dye

A bacterium, Pseudomonas fluorescens, capable to degrade a model chromium azo dye, Acid Yellow 99 (AY99), at the highest efficiency, was isolated from a sludge sample collected from a dyeing factory in Huizhou, China. The optimal conditions of decolorization of AY99 were determined by "response surface method". Under the optimized conditions for decolorizing (0.48 g/L cell dry weight, 0.51 g/L (NH₄₎₂SO₄ and pH = 7.30), the bacterium decolorized 95.7±0.4% of dye. The cells of Ps. fluorescens were immobilized by PVA to build a laboratory scale (1 L) bioreactor. 500 mL synthetic AY99 solution was treated by 201.6 g PVA gel cubes containing 320 mg of bacterial cells. Performance of this bioreactor was evaluated as decolorization (%) efficiency, change of total organic carbon (TOC) content, the Microtox® EC50 test and total dissolved chromium. Besides that, 5 consecutive runs were conducted to evaluate the performance stability of the treatment system. The activity of immobilized cells was stable since the decolorization efficiency had no significant different in the 5 consecutive runs. Lastly, the intermediate(s)/product(s) generated during degradation were subjected to Fourier transform-infrared spectroscopic analysis to detect various functional groups. The results indicated the presence of Cr(III) complexed compounds.