Bioremediation of soil contaminated with toxic mixed reactive azo dyes by co-cultured cells of Enterobacter cloacae and Bacillus subtilis

Azo dyes, known for its toxicity and mutagenicity, are used by textile industries. Bioremediation serves the best alternative treatment process due to its eco-friendly nature and cost-effectiveness. Degradation using individual bacteria promotes azo dye removal, while the degradation is enhanced using the immobilization method. Bio-carrier promotes the attachment of the bacterial strains and increases azo dye degradation. The present study focuses on the biodegradation of Reactive Red (RR), Reactive Brown (RB), Reactive Black dye (RBL), and mixed dyes in a soil slurry bioreactor containing free cells, co-culture, and immobilized cells. The physico-chemical analysis and soil characteristics were determined. The free cells of Bacillus cereus showed degradation of azo dyes - 79.42 ± 0.03% RR, 78.78 ± 0.02% RBL; 70.76 ± 0.03% RB, and 84.89 ± 0.05% of mixed dyes respectively. Enterobacter cloacae free cells resulted in degradation of 72.87 ± 0.01% RR, 75.21 ± 0.01% RBL, 74.50 ± 0.02% RB, and 73.39 ± 0.04% mixed dyes respectively. Co-cultured bacterial strains resulted in 77.18 ± 0.03% RR, 80.27 ± 0.02% RBL, 76.97 ± 0.02% RB and 86.29 ± 0.05% mixed dyes respectively. The immobilization of Bacillus cereus and Enterobacter cloacae on 2% corn starch resulted in 98.4 ± 0.01% degradation of RR, 89.8 ± 0.09% degradation of RB, 99.4 ± 0.05% of RBL, and 98.1 ± 0.08% of mixed reactive dyes respectively.