Abstract:[Background] Azo dyes and their degradation intermediates have certain environmental toxicity. The application of mixed flora to degrade azo dyes is environmentally friendly, whereas the presence of oxygen plays a vital role in the degradation process, which can promote or suppress the biodegradation of azo dyes. [Objective] The effect of oxygen on the azo dye decolorizing solutions were explored, and the influence of oxygen on the decolorization and degradation of azo dyes by mixed flora were investigated. [Methods] Through the decolorization and degradation of seven azo dyes by mixed flora DDMY1 under three culture conditions (aerobic, anaerobic and facultative), the response of their decolorizing solutions to oxygen were discussed. Meanwhile, the degradation products were detected by ultraviolet visible spectrophotometry (UV-vis) and Fourier transform infrared spectroscopy (FTIR). [Results] After 48 h reaction under facultative and anaerobic conditions, several azo dye decolorizing solutions were captured to have the remarkable color restoration after exposure to oxygen, such as Reactive Black 5 and Direct Black 38. The results of UV-Vis analysis showed that the phenomenon of color restoration was derived from the generation of the new substances produced after decolorizing solutions contact with oxygen. In addition, the outcome of FTIR analysis indicated that the mixed flora DDMY1 still had the decolorization and degradation effect on azo dyes despite of color restoration, but the decolorization was not complete. [Conclusion] Under facultative and anaerobic conditions, oxygen had obvious influence on partial azo dye decolorizing solutions, affecting the overall decolorization performance of mixed flora DDMY1 on azo dyes. The study provides a theoretical basis for further research on the complete biodegradation of azo dyes.
