Exploring Aspergillus biomass for fast and effective Direct Black 22-dye removal

Azo dyes are widely used in the textile industry due to their stability and resistance. These properties also make them recalcitrant xenobiotics, toxic, mutagenic, and carcinogenic, even at low concentrations. Considered emerging pollutants, there is an urgency to address mechanisms capable of remediating these contaminants, with Aspergillus fungi standing out as an effective solution. Fifteen strains of Aspergillus were investigated for the decolorization of the tetra azo dye Direct Black 22. The influence of different culture media was evaluated on fungi biomass production, dye concentrations (50–300 mg/L), biomass concentrations (1–5g), and the reuse of biomass in continuous batches. The strains that stood out the most were Aspergillus japonicus URM 5620, Aspergillus niger URM 5741, and A. niger URM 5838. Obtaining biomass in less nutrient-rich medium favored decolorization by forming more organized pellets. The live biomass of these fungi was 59% more efficient than the dead biomass. The decolorization efficiency was not affected at lower dye concentrations, showing a decrease in decolorization only when the concentration reached 300 mg/L. Increasing the amount of biomass resulted in proportionally greater decolorization. Even with just 1 g of biomass, the three fungi could remove more than 90% of the dye in less than 60 minutes, and with 5 g, the dye was completely removed in 10 minutes. Thebiomass was reused in three consecutive decolorization cycles, and the fungus that best withstood the cycles was A. niger URM 5741. These results demonstrate the potential of the genus Aspergillus fungi tested in this study as sustainable and efficient biosorbents for the remediation of azo dyes such as Direct Black 22, with potential for colored industrial effluent treatment.