Optimization of the decolorization conditions of Rose Bengal by using Aspergillus niger TF05 and a decolorization mechanism

Aspergillus nigerTF05 was applied to decolorize Rose Bengal dye. The effects of carbon source, nitrogen source, metal ion and spore concentration on Rose Bengal treatment with A. nigerTF05 were studied. A Plackett-Burman design (PBD) and a uniform design (UD) were used to optimize the decolorization conditions of A. niger TF05 and enhance its decolorization effect. The mechanism of Rose Bengal decolorization by A. nigerTF05 was examined by analysing degradation products via UV-visible light spectroscopy, IR spectroscopy and GC-MS. The best decolorization effect was achieved in the single factor test with glucose and ammonium chloride as carbon and nitrogen sources, respectively. Mg2+ was an essential ion that could improve the mould ball state and adsorption efficiency if the spore concentration was maintained at 10(6) spores ml(-1). The optimal decolorization conditions obtained using the PBD and UD methods were 11.5 g l-1 glucose, 6.5 g l(-1) ammonium chloride, 0.4 g l(-1) magnesium sulphate, pH 5.8, 28 degrees C, 140 r.p.m. rotational speed, 0.18 g l(-1) dye concentration, 0.5 ml of inocula and 120 h decolorization time. Under these conditions, the maximum decolorization rate was 106%. Spectral analysis suggested that the absorption peak of the product changed clearly after decolorization; GC-MS analysis revealed that the intermediate product tetrachlorophthalic anhydride formed after decolorization. The combined use of the PBD and UD methods can optimize multi-factor experiments. A. nigerTF05 decolorized Rose Bengal during intracellular enzymatic degradation after adsorption.