Decolorization of Acid Orange 7 by extreme-thermophilic mixed culture

Although a large amount of textile wastewater is discharged at high temperatures, azo dye reduction under extreme-thermophilic conditions by mixed cultures has gained little attention. In this study, Acid Orange 7 (AO7) was used as the model azo dye to demonstrate the decolorization ability of an extreme-thermophilic mixed culture. The results showed that a decolorization efficiency of over 90% was achieved for AO7. The neutral red (NR, 0.1 mM) could promote AO7 decolorization, in which the group of Cell + NR offered the highest decolorization rate of 1.568 1/h and t_1/2 was only 0.44 h, whereas after CuCl₂ addition, the decolorization rate (0.141 1/h) was lower and t_1/2 (4.92 h) was much longer. Thus, CuCl₂ notably inhibited this process. Caldanaerobacter (64.0%) and Pseudomonas (25.4%) were the main enriched bacteria, which were not reported to have the ability for dye decolorization. Therefore, this study extends the application of extreme-thermophilic biotechnology.