Decolorization ability and microcosmic biosorption process of reactive dyes with fungus Penicillium oxalicum

The decolorization ability and adsorption process of seven water-soluble reactive dyes, namely Reactive Turquoise Blue KN-G, Reactive Black K-BR, Reactive Turquoise M-GB, Reactive Brilliant Blue M-BR, Reactive Violet K-3R, Reactive Dark Blue K-R and Reactive Turquoise Blue K-GL, with Penicillium oxalicum were studied when the strain was growing in the simulative dye wastewater. It was found from adsorption experiments that the growing Penicillium oxalicum possessed excellent adsorption ability to the reactive dyes. At lower initial dye concentration (200 mg/L), the average decolorization rate of seven dyes reached 93.0%, at higher initial dye concentration (400 mg/L), the decolorization rates of Reactive Turquoise Blue KN-G and Reactive Turquoise M-GB were 99.7% and 99.9% respectively. Spectrophotometric analysis of supernatants and tracing of Cu²⁺ (which is contained in the dye molecules) concentration in the supernatants indicated that the decolorization of dyes by Penicillium oxalicum biomass involved an adsorption process. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images illustrated that the hyphae of the fungus swelled, the structure of the cell wall was reconstituted and the thickness of the cell wall increased about 10-15 folds. The cell wall played an important role in dye biosorption by growing fungus. It not only offered the major biosorption sites for the dyes, but also provided routeway for the dye molecules to enter the cells.