Removal of orange G dye by Aspergillus niger and its effect on organic acid production.

Azo dyes have been found in wastewater from textile industries. These compounds continuously persist in the environment for long periods of time and may be toxic for living beings. An alternative treatment for dye removal that has proven to be effective is aerobic treatment with fungi. In this study, Aspergillus niger was investigated as a mechanism to remove orange G (OG). Removal of 200 mg/L of OG by A. niger biomass was carried out in solid and liquid medium, which showed a positive correlation between A. niger growth and dye removal. In liquid media what was proved is that the efficiency of OG removal by A. niger depends on its concentration; at 200 mg/L of OG remove by degradation and at 400 mg/L by processes as sorption and degradation. During OG removal, the generation of organic acids by A. niger was modified compared to constitutive generation, one of the modifications was the increase of gluconic acid production and the decrease of acids involved in the Krebs cycle, as well as the null detection of oxalic acid. The monitoring of organic acids by high-performance liquid chromatography (HPLC) was important because some of them have been linked to dye removal.

Effect of fungal co-cultures on ligninolytic enzyme activities, H2O2 production, and orange G discoloration.

In this study, the effects of Aspergillus niger in coculture with the basidiomycetes, Trametes versicolor, T. maxima, and Ganoderma spp., were studied to assess H2O2 production and laccase (Lac), Lignin Peroxidase (LiP), and manganese peroxidase (MnP) activities. The results indicated that maximum discoloration was of 97%, in the T. maxima and A. niger coculture, where the concentration of H2O2 was 5 mg/L and 6.3 mg/L in cultures without and with dye, respectively. These concentrations of H2O2 were 1.6- and 1.8-fold higher than monocultures of T. maxima (3.37 mg/L) and A. niger (3.87 mg/L), respectively. In the same coculture, the LiP and MnP enzyme activities also increased 12-fold, (from 0.08 U/mg to 0.99 U/mg), and 67-fold, (from 0.11 U/mg to 7.4 U/mg), respectively. The Lac activity increased 1.7-fold (from 13.46 U/mg to 24 U/mg). Further, a Box-Behnken experimental design indicated a 1.8-fold increase of MnP activity (from 7.4 U/mg to 13.3 U/mg). In addition, dye discoloration regression model obtained from the Box-Behnken experimental design showed a positively correlation with H2O2, (R2 = 0.58) and a negatively correlation with Lac activity (R2 = -0.7).