Isolation and Identification of Azo Dye–Degrading Microorganisms from Textile Wastewater Treatment Sludge

Abstract

    This study aimed to isolate, qualitatively screen, and identify azo dye–degrading microorganisms from the activated sludge of a textile wastewater treatment system. Congo Red (100 mg/L) was used as the sole selective dye in Minimal Salt Medium to enrich potential degraders. A total of ten bacterial isolates (M1–M10) were successfully obtained, all exhibiting decolorization halos ranging from 22 to 46 mm on MSM agar. Among them, isolates M1 and M8 demonstrated the strongest activity, forming clear zones of 46 mm and 44 mm after 48 hours, respectively. Molecular identification through 16S rRNA gene sequencing revealed that M1 shared 99.87% similarity with Bacillus subtilis, while M8 shared 99.86% similarity with Bacillus licheniformis. Both species are known for their production of extracellular oxidative enzymes, such as laccases and peroxidases, which play key roles in azo bond cleavage and aromatic amine detoxification. These findings highlight the presence of native, dye-adapted Bacillus strains with strong decolorization capacity in textile wastewater sludge and provide foundational data for developing bioaugmentation agents applicable in sustainable textile effluent treatment systems.