Removal of different vat dyes by Aspergillus niger: A comparative study focusing on the molecular structure

Vat dyes are the most commonly used dyes in the denim industry. Since the pollution of the textile industry is a worldwide problem, Aspergillus niger was used in this study, to treat vat dye wastewater by pre-culture and simultaneous-culture methods. A comparison between the two biosorption techniques used showed that pre-culture was about 30% more efficient than simultaneous culture. The adsorption capacity was determined using the Langmuir and Freundlich adsorption models, with Langmuir proving to be the most suitable model. The high saturation capacity of 121.35 mg/g for C.I. Vat Brown 1 calculated with the Langmuir adsorption model indicated that A.niger is a suitable sorbent for vat dye wastewater. To investigate the influence of dye structure on biosorption efficiency, eight vat dyes with different chemical characteristics were used. The results showed that the complete decolorization time was reduced by 200 and 150 min for planar and non-planar structures, respectively, due to the reduction of molecular mass, indicating that molecular mass is probably the dominant factor in vat dye removal. In addition, planar structures resulted in a 50-min reduction in biosorption time. The possible adsorption sites were analyzed by Fourier transfer infrared analysis. The results showed that the amino and carboxyl groups of the fungus could serve as sorption sites for vat dyes through hydrogen bonding."