Microalgal and activated sludge processing for biodegradation of textile dyes

The textile industry contributes substantially to water pollution. To investigate bioremediation of dye-containing wastewater, the decolorization and biotransformation of three textile azo dyes, Red HE8B, Reactive Green 27, and Acid Blue 29, were considered using an integrated remediation approach involving the microalga Chlamydomonas mexicana and activated sludge (ACS). At a 5 mg L−1 dye concentration, using C. mexicana and ACS alone, decolorization percentages of 39%–64% and 52%–54%, respectively, were obtained. In comparison, decolorization percentages of 75%–79% were obtained using a consortium of C. mexicana and ACS. The same trend was observed for the decolorization of dyes at higher concentrations, but the potential for decolorization was low. The toxic azo dyes adversely affect the growth of microalgae and at high concentration 50 mg L−1 the growth rate inhibited to 50–60% as compared to the control. The natural textile wastewater was also treated with the same pattern and got promising results of decolorization (90%). Moreover, the removal of BOD (82%), COD (72%), TN (64%), and TP (63%) was observed with the consortium. The HPLC and GC-MS confirm dye biotransformation, revealing the emergence of new peaks and the generation of multiple metabolites with more superficial structures, such as N-hydroxy-aniline, naphthalene-1-ol, and sodium hydroxy naphthalene. This analysis demonstrates the potential of the C. mexicana and ACS consortium for efficient, eco-friendly bioremediation of textile azo dyes. [Display omitted] •Activated sludge and C. mexicana effectively degrade Red HE8B, RG-29, and AB-29 azo dyes.•Consortium enhances decolorization: Red HE8B 1.21x, RG-29 1.69x, AB-29 1.29x.•The growth inhibition was 50–60% in dyes contaminated wastewater.•HPLC and GC-MS confirmed effective degradation of azo dyes into N-hydroxy-aniline, naphthalene derivatives.